Tebufenozide in the product Mimic 700 WP Insecticide, Mimic 240 SC Insecticide

SUMMARY

The Australian Pesticides and Veterinary Medicines Authority (APVMA) has considered an application to register the new chemical tebufenozide for the control of light brown apple moth on apples, pears and grapevines;  codling moth on apples and pears;  and pear looper and pear slug on pears, in all States and Territories as specified in the directions-for-use table on the products' labels.

This publication outlines the regulatory considerations and summarises the data reviewed by the APVMA for the proposed registration of tebufenozide.  Before deciding whether to approve this product for use in Australia, the APVMA invites public comment.  Comments should be submitted by 6 June 1997 to the APVMA at the address indicated on page 1.

The APVMA has assessed the data submitted by the applicant in support of this use of tebufenozide and provides the following information for public comment.

Agricultural aspects

MIMIC 700 WP INSECTICIDE is a wettable powder product containing 700g/kg of the new hydrazide insecticide, tebufenozide. MIMIC 240 SC INSECTICIDE is a suspension concentrate product containing 240g/L tebufenozide The new products have been developed in an attempt to provide an extra tool in integrated pest management and insecticide resistance management.

The products, when applied at label rates, have been shown to give good control of:

  • light brown apple moth on apples, pears and grapes;
  • codling moth on apples and pears; and
  • pear looper and pear slug on pears.

Environmental aspects

Tebufenozide applied by air blast or boom sprayers to pome fruits or grapevines during spring-summer is likely to result in significant contamination of orchard or vineyard soil.  Spray drift is likely to be the main means of off-site contamination.

The main means of degradation of tebufenozide is likely to be microbial degradation, with hydrolysis or direct photolysis unlikely to be significant under relevant environmental conditions.  Indirect photolysis may make a small contribution to degradation in water and on soil surfaces exposed to sunlight.  Tebufenozide is likely to have low (2-6 weeks) to moderate persistence (DT50 = 6 weeks to 6 months) in soil and sediment under Australian conditions, but should not accumulate in soil and is unlikely to bioaccumulate in aquatic organisms.  Depending on conditions, it may be readily to slightly degradable in water (DT50 2-3 to 80 days).  Major metabolites identified were a ketone and two carboxylic acid transformations of the tebufenozide molecule, which ultimately degrade to CO2.  Tebufenozide will not tend to volatilise from moist or dry surfaces and once adsorbed, has low mobility in soil, though it may be mobile when freshly applied to light soil low in organic matter.  Carboxylic acid metabolites of tebufenozide are relatively more mobile, but little leaching of either the parent compound or its metabolites was found in field studies.

Tests have found that tebufenozide TGAC is practically non-toxic to birds (bobwhite quail and mallard duck).  Tebufenozide has moderate to high toxicity to certain aquatic species, particularly Crustaceans in the Order Cladocera (including Daphnia magna and others), the bivalve mollusc Eastern oyster (Crassotrea virginica), and potentially algae (Scenedesmus subspicatus affected in a laboratory study, but no overall effect on phytoplankton in a Canadian lake study).  However, it is less toxic to many other aquatic species tested, including other Crustacean species tested (copepods, the amphipod Gammarus sp., and the mysid shrimp), and aquatic insects.  The tests available indicate that tebufenozide has low toxicity to terrestrial adult and larval stages of invertebrates other than insects of the Order Lepidoptera, including honey bees, mites, spiders, various non-lepidopteran insects and earthworms.  It has low toxicity to mammals.  Of the three major metabolites, the two carboxylic acid metabolites are likely to be significantly less toxic than tebufenozide to fish and daphnids and are not insecticidally active, whereas the ketone metabolite has some ecdysteroid activity, but significantly less than tebufenozide.

Estimated worst case dietary concentrations are well below the acute oral, 5-day dietary and one-generation reproduction lowest effect concentrations for bobwhite quails and mallard ducks, hence tebufenozide is not likely to present a hazard to birds ingesting these residues.  Similarly, acute or chronic toxicity in mammals is highly unlikely.

Worst case analyses indicate that there is a potential hazard to aquatic invertebrates such as the cladoceran Daphnia magna and the bivalve mollusc, Eastern oyster (Crassotrea virginica) from a single direct overspray incident or from repeated spraydrift contamination.  Laboratory study results also indicate a potential hazard to the green alga Scenedesmus subspicatus, but two mesocosm studies indicated no overall effects of tebufenozide on phytoplankton.  Therefore toxicity to algae appears unlikely under field conditions, but a potential hazard to certain algal species cannot be ruled out, as these studies did not report population composition.  However, direct contamination and repeated spray drift contamination are unlikely.

Evaluation of worst case situations with fish indicate that expected environmental concentrations are less than 0.1 X acute or chronic LC50 estimates, hence there is no hazard likely to fish, even with repeated direct spray or spraydrift contamination.  There is also no hazard likely to aquatic insects or non-cladoceran Crustacea (amphipods, copepods, mysid shrimp).

Tebufenozide has low toxicity to insects other than Lepidoptera, spiders, mites and earthworms.  This selectivity encourages its use in IPM programs.

Native plants are only likely to be reached by spraydrift, rather than direct spray, and the lack of phytotoxicity in a wide range of crop species suggests that even if reached by spray, Australian native plants are unlikely to be harmed.

Toxicology

Tebufenozide, the active ingredient of MIMIC 700 WP Insecticide and MIMIC 240 SC Insecticide, has low acute oral, dermal and inhalational toxicity.  It does not cause skin or eye irritation, or skin sensitisation.  The product, MIMIC 700 WP Insecticide, has low oral, dermal and inhalational toxicity, and causes slight skin irritation and skin sensitisation and moderate eye irritation.  MIMIC 240 SC Insecticide is expected to be of low oral and dermal toxicity, but a moderate to severe eye irritant and a slight to moderate skin irritant.  MIMIC 240 SC is not expected to be a skin sensitiser. 

Following repeated administration of tebufenozide, regenerative anaemia was consistently observed in mice, rats and dogs, together with increased haemosiderin deposition in the liver and spleen at moderate to high doses.  There was no evidence of oncogenic potential following long-term dietary exposure to tebufenozide in mice or rats.  Tebufenozide does not cause genetic damage in a number of in vitro or in vivo studies.  No effects on foetal development were observed in rats or rabbits.  In rats, tebufenozide caused decreased implantations in rats at high doses, which were toxic to the parental animals.  There was no evidence of neurological effects in rats.

Based on an assessment of the toxicology and the potential dietary intake of residues, no adverse effects on human health are likely to occur from the use of MIMIC 700 WP Insecticide or MIMIC 240 SC Insecticide in accordance with label directions.

Residues in food

Residue data from apple, pear and grape studies conducted in Australia using use patterns at rates of 1.6 to 2 times those proposed for apples and pears and at the rate proposed for grapes but with more applications than recommended, showed that residues of tebufenozide were below 2.0 mg/kg in the treated fruit or grapes after a 28 day withholding period. Because the Australian residue data were not generated according to the proposed Australian use patterns but were from higher rates or used larger numbers of applications than proposed, temporary MRLs were established for pome fruit and grapes. Animal and poultry metabolism studies showed that tebufenozide was extensively metabolised and excreted.  Residues of tebufenozide in animal commodities arising from consumption of produce made from treated fruits are expected to be non-measurable on the basis of the results of the animal metabolism studies and calculated dietary intakes of residues.  An appropriate animal grazing/feeding withholding period restraint is intended to ensure that animal consumption of treated fruits will not result in animal commodity residues.

Trade

Tebufenozide is registered in 16 countries for use on pome fruit or apples and/or grapes with the USA having an import tolerance for tebufenozide residues in apples.  Maximum Residue Limits in these countries are £1 mg/kg after multiple applications and withholding periods of the order of 14-45 days.  The recommended temporary Australian MRLs of 2 mg/kg  are greater than 1 mg/kg and exported produce would have to comply with the established MRLs or requirements of the importing country.  Maximum residue limits for dried grape fruits and for wine have generally not been established overseas and, especially in the case of exported wine, care will be needed to ensure that any tebufenozide residues present in exported produce comply with the importing country's tolerances.  No Codex MRLs have been established for tebufenozide at this time.

The data presented indicated that use of the product according to the proposed  use patterns would not be expected to result in the recommended MRLs being exceeded.  Measurable animal commodity residues are not expected and the proposed use is considered to present little hazard to Australian export trade provided care is taken to ensure that the concentrations of tebufenozide residues present in exported commodities do not exceed the tolerances established by importing countries.

Occupational health and safety

Worksafe Australia has conducted a risk assessment on Mimic 240 SC Insecticide, containing tebufenozide at 240 g/L as a suspension concentrate and Mimic 700 WP Insecticide, containing 700 g/kg tebufenozide as a wettable powder in water-soluble sachets, for use on apple and pear crops and grapevines.  Mimic 240 SC Insecticide and Mimic 700 WP Insecticide can be safely used by workers when handled in accordance with the control measures indicated in this assessment.

Tebufenozide is not on the National Occupational Health and Safety Commission (NOHSC) List of Designated Hazardous Substances.  Bayer Australia Limited has determined that tebufenozide is not a hazardous substance according to NOHSC criteria.  Based on available information, Mimic 240 SC Insecticide and Mimic 700 WP Insecticide cannot be determined to be hazardous substances.

Tebufenozide products are imported, however should formulation be carried out in Australia in the future, workers will need to be protected by engineering controls, such as air extraction and enclosed vessels, the wearing of personal protective equipment, by adopting safe work practices and receiving adequate training.  Testing of chemicals should be done under fume hoods.

Mimic 240 SC Insecticide can be expected to be of low oral and dermal toxicity, a moderate to severe eye irritant and a slight skin irritant.  It is not expected to be a skin sensitiser.  Mimic 700 WP Insecticide is expected to be of low oral, dermal and inhalation toxicity.  It can be slightly irritating to the skin and moderately irritating to the eyes, and a slight skin sensitiser.  Instructions and safety directions on the product labels enable safe use of the products in the short and long term.  These include the use of cotton overalls, PVC gloves and face shield or goggles for Mimic 240 SC Insecticide.  Personal protective equipment is not needed when using Mimic 700 WP Insecticide because it is presented in water soluble sachets.

Top

INTRODUCTION

This publication provides a summary of the data reviewed and an outline of the regulatory considerations for the proposed application of the chemical tebufenozide as an insecticide for the control of light brown apple moth on apples, pears and grapevines;  codling moth on apples and pears;  and pear looper and pear slug on pears.  It also seeks public comment prior to the chemical product being approved for use in Australia.

Responses to public consultation will be considered prior to registration of the product.  They will be taken into account by the APVMA in deciding whether the product should be registered and in determining appropriate conditions of registration and product labeling.

Copies of full technical reports on occupational health and safety aspects, environmental impact, and residues in food are available from the APVMA on request.  They can also be viewed at the APVMA Library located at the APVMA's offices on Level 1, Computer Associates House, 10 National Circuit, Barton, ACT 2604.

Written comments should be received by the APVMA by 9 June 1997.  They should be sent to:

Mr Graeme Barden

Senior Product Evaluator

Agricultural Chemicals Registration

National Registration Authority

PO Box E240

KINGSTON ACT 2604

FAX: (06) 272 3218

Applicant

Bayer Australia Limited has applied for registration of two insecticide products containing a new active constituent, tebufenozide, a hydrazide insecticide.

Product details

Tebufenozide will be marketed under the trade names MIMIC 700 WP INSECTICIDE, a wettable powder product containing 700g/kg tebufenozide, and MIMIC 240 SC INSECTICIDE, a suspension concentrate product containing 240g/L tebufenozide.

MIMIC 700 WP INSECTICIDE and MIMIC 240 SC INSECTICIDE will be imported fully formulated and packed outside Australia.

Bayer Australia Limited intends to market MIMIC 700 WP INSECTICIDE and MIMIC 240 SC INSECTICIDE in all States and Territories for the control of certain lepidopterous pests of apples, pears and grapevines.

Top

CHEMICAL PROPERTIES

Active constituent

The chemical active constituent tebufenozide is manufactured in the Netherlands and has the following properties:

Common name (ISO): tebufenozide
Chemical name:

4-ethylbenzoic acid-N'-tert-butyl-N'- (3,5-dimethyl-benzoyl)hydrazide (IUPAC) Benzoic acid, 3,5-dimethyl-1-(1,1-dimethylethyl)-2-(4-ethyl-benzoyl)hydrazide (CA)

Product Names:  

   Mimic 700 WP Insecticide, and
Mimic 240 SC Insecticide

CAS Registry Number: 112410-23-8
Empirical formula:   C22H28N2O2
Molecular weight:   352.48
Physical form:   white powder
Density:: Not supplied
Melting point:     191 - 191.5 C
Boiling point:  
Specific gravity:  
Octanol/water partition coefficient (Kow): log mean Kow = 4.23       
Vapour pressure at 25C:   2.7 x 10-6 Pa
Structural formula:

Structural formula

Top

AGRICULTURAL ASSESSMENT

Justification for use

MIMIC 700 WP INSECTICIDE is a wettable powder product containing 700g/kg of the new hydrazide insecticide, tebufenozide. MIMIC 240 SC INSECTICIDE is a suspension concentrate product containing 240g/L tebufenozide.

Insecticide resistance in light brown apple moth has the potential to cause significant damage to the pome fruit industry.  The new products have been developed in an attempt to provide an extra tool in integrated pest management and insecticide resistance management.

Registration is supported by Australian agricultural authorities.

Proposed use pattern

Tebufenozide is proposed to be used to control light brown apple moth on apples, pears and grapevines;  codling moth on apples and pears;  and pear looper and pear slug on pears.  All uses are proposed for all states and territories, as specified in the directions for use table on the products' labels (See Appendix 1).

MIMIC 700 WP INSECTICIDE is available in an 860g packsize, containing 10 x 86g measure packs (being water soluble).  The measure packs are of a size appropriate the rates required on the label.  MIMIC 240 SC INSECTICIDE is available in a 1L packsize.  Use rates are 25mL/100L for apples, pears and grapevines (or 500mL/ha for grapevines).  The addition of a wetting agent is recommended for grapevines.

A harvest withholding period of 4 weeks have been recommend for all treated crops - apples, pears and grapevines.  These appear on the products' labels (Appendix 1).

Evaluation of efficacy

Data presented by Bayer Australia Limited supported claims that MIMIC 700 WP INSECTICIDE and MIMIC 240 SC INSECTICIDE adequately control light brown apple moth in apples, pears and grapevines, and that they are equivalent to Gusathion and Lorsban.

Claims for control of pear looper and pear slug were supported by the data provided, but submission of further confirmatory data was recommended.

Data indicated inconsistent suppression of coddling moth.  The label indicates that suppression may occur when treating orchards with low codling moth pressure (Appendix 1).

Phytotoxicity

There was no evidence of phytotoxicity of the formulations on target crops.

Resistance management

The labels recommend that MIMIC 700 WP INSECTICIDE and MIMIC 240 SC INSECTICIDE be applied at strict 14 day intervals.  Two sprays only are recommended for grapevines, with a possible third spray for late generation larvae.  A maximum of six sprays per season is recommended for apples and pears.

State agriculture authorities are satisfied that MIMIC 700 WP INSECTICIDE and MIMIC 240 SC INSECTICIDE are compatible with integrated pest management, and that label instructions are adequate.

Top

ENVIRONMENTAL ASSESSMENT

Introduction

Bayer Australia Ltd has applied to the APVMA for registration of the end use products Mimic(r) 700 WP Insecticide and Mimic(r) 240 SC Insecticide, and the new technical grade active ingredient (TGAC) tebufenozide which they contain.  Registration is sought for the control of light brown apple moth (LBAM - Epiphyas postvittana) on pomefruit and grapevines, for control of pear looper (Chloroclystis spp.) and pear and cherry slug (Caliroa cerasi) on pears, and for suppression of codling moth (Cydia pomonella) on pomefruit.

Tebufenozide mimics the natural arthropod moulting hormone, 20-hydroxyecdysone and can therefore be characterised as an ecdysone agonist, or an ecdysonoid.  It causes caterpillars to cease feeding and undergo premature and incomplete moulting, dying of dehydration and starvation.  Exposure to a sublethal dose has been observed to produce sterile adults.

Environmental Fate

It is proposed that tebufenozide be applied as a dilute or semi-concentrate spray at rates up to 181 g.ha-1 up to 6 occasions per year in pomefruits, and at rates up to 120 g.ha-1 a.i. up to 3 occasions per year in grapes.  Application is likely to involve trailer mounted pneumatic spray equipment (air blasters) with a fine to medium droplet size.  Residues would be expected on plant leaves, the crop itself and soil surfaces.  Overspray, spraydrift and run-off are likely to occur.  Surface water and uncultivated land may be contaminated through spraydrift and run-off.

Hydrolysis

A laboratory study reported indicated that tebufenozide hydrolyses only slightly (DT50 > 1-2 years) at pH 5-9, hence hydrolysis under environmental conditions is likely to be insignificant.

Photolysis

Laboratory studies indicate that little or no photolysis of tebufenozide occurs in deionised water at pH 7.  One study indicated a degradation half-life of 67 days (slightly degradable) in natural pond water, possibly indicating indirect photolysis due to the presence of photosensitisers, but the water may not have been sterile, hence significant microbial degradation may have occurred.  Degradation in these studies was much slower than occurred in another brief study with continuous UV-A irradiation of tebufenozide solutions, but is consistent with the absence of significant absorption by tebufenozide of UV-A and UV-B radiation, i.e. at wavelengths reaching the ground (peak UV absorbance at l = 233-234 nm is in the UV-C band).  Furthermore, the extent to which aqueous photolysis occurs in practice may be reduced to some extent by adsorption of tebufenozide to sediment and by turbidity, which is common in Australia in dam and channel water.

Tebufenozide may also be slightly degradable by photolysis on soil surfaces, with a first order DT50 of 98 days (but note that degradation may have been biphasic) in a single experiment with one soil.

Thus direct photolysis of tebufenozide is unlikely to be significant under relevant environmental conditions, but indirect photolysis may make a small contribution to degradation in water and on soil surfaces exposed to sunlight.

Soil/aquatic metabolism

Microbial degradation is likely to be the major means of degradation of tebufenozide. Degradation half-lives for tebufenozide in an aerobic soil metabolism study were 105 days in a loam soil and 704 days in a sandy loam.  There was no clear explanation for the large difference between the soils.  Degradation rates in an aerobic aquatic metabolism study were comparable to the lower value in the aerobic soil study, with whole system degradation half-lives of 100 and 101 days in a clay loam and a silty loam soil, respectively.  The whole system degradation half-life in an anaerobic aquatic metabolism study with a silty loam pond sediment was 179 days.  In both the aquatic metabolism studies, tebufenozide persisted in water at > 10% of applied 14C for > 90 days, with relatively slow initial adsorption to sediment (18-39% of applied 14C still present in water as tebufenozide after 3 days of incubation).

Several metabolites were common to the aerobic soil and aerobic and anaerobic aquatic degradation studies, three of which at times exceeded 10% of applied 14C and were identified (a ketone and two carboxylic acid transformations of the tebufenozide molecule).  The ketone was also found in an aqueous photolysis study and was suspected as a contaminant in an hydrolysis study.  One of the carboxylic acids reached 35.5% (day 365) of applied 14C in the silty loam soil in the aerobic aquatic study (peak concentration range 3.7-7.7% in the soil study, 5.8-35.5% in the aerobic aquatic study and 11.6% in the anaerobic aquatic study).  The hypothesised metabolic pathway was the same for both aerobic and anaerobic conditions.  Most of the metabolites occurred at some time with each of the three radioactive labels and no cleavage products were identified.  As there is significant mineralisation (see below), presumably rapid breakdown follows once cleavage occurs.

Except for the sandy loam in the aerobic soil metabolism study, significant mineralisation occurred of both the phenyl rings and also the tertiary butyl moiety, demonstrated by the use of 3 different 14C-label positions.  14C-CO2 evolution after 12 months of incubation was 54-62% of applied 14C in the loam in the aerobic soil metabolism study, 19-47% in the aerobic aquatic metabolism study and 17% in the anaerobic aquatic metabolism study, but only 2-5% of applied 14C in the case of the sandy loam in the aerobic soil metabolism study.  Soil residues after initial solvent extraction peaked at 12-34% of applied 14C, and were shown to include some parent compound (up to ~6% of applied 14C).

Mobility

Physico-chemical properties of tebufenozide indicate that it will not tend to volatilise from moist or dry surfaces.

Laboratory adsorption/desorption studies in a total of seven soils indicated that tebufenozide has low to medium mobility potential in soil (KOC (adsorption) = 161-894 depending on soil type and temperature).  Once adsorbed, tebufenozide is more tightly held (KOC (1st desorption) = 568-1,227 in one study, indicating that the substance has low mobility, and KOC (desorption) = 7,632-8,806 in a separate study, indicating it is immobile).  A laboratory study indicated that the major carboxylic acid metabolite is likely to have medium to high mobility in soil (KOC (adsorption) = 76-156).

Groundwater Ubiquity Score estimates for various soils calculated using laboratory adsorption/desorption data and a DT50 for tebufenozide of 105 days (similar to most soils in the laboratory degradation studies) indicate that tebufenozide is a transitional to probable leacher, while the shorter DT50 indicated by field studies (44 days) indicates that tebufenozide is an improbable to transitional leacher. 

A laboratory aged (1 month) leaching study was consistent with these studies, indicating that the extent of downward movement in soil columns was associated with soil texture and organic matter content.  Little downward movement occurred in a loam soil high (16.7%) in organic matter, and 8%, 23% and 26% of recovered radioactivity appeared in eluate from a loam, sandy loam and sand, respectively (0.8-1.2% organic matter).  The major carboxylic acid metabolites were shown to be relatively more mobile than the parent compound or major ketone metabolite, little (< 2% of recovered radioactivity) tebufenozide being present in the eluate, except in that from the sand (19% of recovered radioactivity).

Thus these studies indicate that little downward movement of parent compound would be expected where the surface organic matter content is high, whereas significant downward movement of polar metabolites and to a lesser extent, parent compound, would be expected in soils low in organic matter content, particularly when they are light in texture.

Field dissipation

Two terrestrial field dissipation studies in the USA simulated seasonal applications of tebufenozide to vegetables and walnuts, but on bare soil.  One USA and two Canadian studies investigated dissipation of tebufenozide in forest environments, including foliage, surface litter, soil and/or lake, pond and stream water and sediment. 

Dissipation in terrestrial and forest soils

In five field or mesocosm terrestrial dissipation studies in forests or in bare horticultural soils, DT50s for tebufenozide in soil under aerobic conditions ranged from 23 days to 56 days, with an overall average of 42 days. The estimated DT50s were therefore consistent with each other and with laboratory data, despite cool to cold (frozen) conditions occurring during winter in the forest studies.  Estimated dissipation half-lives for tebufenozide in soil under aerobic conditions in laboratory soil metabolism studies were 105 days (recalculated to 66 days by the US EPA) in one study (California loam) and 704 days in another (Pasquotank sandy loam).  Short term (30 days - too short for reliable estimation of degradation) laboratory leaching studies indicated DT50s of 32.5-63.1 days. Environment Australia recognises that the 704 day half-life from the Pasquotank sandy loam study is much larger than that from other studies under aerobic conditions and accepts the applicant's claim that this study was probably flawed (pp 10-13 of this report).

With a DT50 of 80-224 days, tebufenozide was significantly slower to dissipate in litter, which had a very high (≥80%) organic matter content.  One forest study indicated that dissipation in surface litter and soil within a forest was affected by residues in foliage either being washed off over time, or reaching the ground in falling leaves and needles: presumably such an effect would be evident to a small extent in orchards and vineyards.

Aquatic dissipation

There was a large difference in the dissipation rate of tebufenozide in aquatic situations, presumably associated with the initial concentrations and water depth present, the nature of bottom sediments (organic matter content and particle size distribution), the presence of submerged plant surfaces such as moss, and presumably, the overall biological activity of the system.

In mesocosm studies in a cold boreal lake with an organic, flocculent (28.2% organic matter, sand:silt:clay = 10:55:35) sediment, tebufenozide dissipated relatively slowly from treated lake water, with a dissipation half-life of ~80 days.  Adsorption to sediment was important in dissipation from the lake water over the first few weeks, as it was in laboratory aquatic metabolism studies: sediment concentrations of tebufenozide increased for 4-5 weeks before declining slowly (from peak levels in sediment, tebufenozide DT50 estimates made by the reviewer were 119-453 days, being very slow at the highest rate tested).  These estimates are somewhat slower than DT50 estimates in aquatic systems under laboratory conditions (whole system and water DT50 96.1-105 days and ~40 days respectively under aerobic conditions; whole system DT50 179 days under anaerobic conditions).  A major contributing factor to the slow dissipation in the lake study may have been the low ratio between sediment and water in the mesocosm study (i.e. high tebufenozide concentrations in 2-3 m deep water).  Another mesocosm study under littoral lake conditions (water 0.8-1.0 m deep above bladderwort and pondweed) indicated DT50s in water of 32.2-35 days, similar to the laboratory aerobic aquatic study.

In contrast, in forest ponds and streams in two other field dissipation studies in Canada and the USA, dissipation in water was much faster, with half-lives of 1-3 days.  In the Canadian field study, submerged plants such as moss were shown to be a major sink for residues in water, whereas residue concentrations in the coarse, low organic matter content (2.6%) sediments were very low and not persistent.

Mobility of parent compound and metabolites in the field

Although the USA field dissipation studies included soils which were light in texture and low in organic matter content, measurable levels of tebufenozide and its metabolites were largely confined to the surface 15 cm of soil and generally only found in trace quantities below 30 cm.  Thus little leaching of tebufenozide or the ketone metabolite was detected, and concentrations of the more mobile carboxylic acid metabolites were very low below 30 cm.  The USA forest study indicated little or no detectable movement of metabolites below 7.6 cm  The Canadian terrestrial mesocosm study found very little leaching occurred in a soil relatively high (3.9%) in organic matter content, with residues largely confined to the surface 2.5 cm of sprayed soil.  However, the laboratory leaching studies suggest that greater leaching of tebufenozide and its metabolites might be expected in light soils low in organic matter under a large rainfall or irrigation event.

Accumulation in soil

From laboratory degradation and field dissipation studies, a field DT50 of 23-105 days appears the most likely situation in soil under aerobic conditions in Australia.  This indicates that there should be little or no build-up of active ingredient (a maximum of <0.01%, 0.24% and 9% of tebufenozide remaining from year to year in the surface 15 cm of soil with a DT50 of 23, 42 and 105 days, respectively).  This is supported by the very low or undetectable levels found in soil by one year after application in the field dissipation studies.  Somewhat longer half-lives might occur under anaerobic conditions, in sediment or in surface litter, but little build-up of tebufenozide would still be expected (maximum of 155 ppb remaining from year to year in the surface 15 cm of soil with a DT50 of 179 days).

Bioconcentration

Estimated bioconcentration factors for tebufenozide from a study with bluegill sunfish were 42-70, i.e. in the "slightly concentrating" range according to Mensink et al. (1995), and depuration is rapid and proceeds towards completion.

Environmental Effects
 

Avian toxicity

Tebufenozide was practically non-toxic to bobwhite quail by the single oral dose route (LD50 values greater than the highest a.i. doses tested of 2,150 mg.kg‑1 body weight), and was also practically non-toxic to both bobwhite quail chicks and mallard ducklings with 5-day dietary exposure followed by 3 days observation (LC50 > 5,000 mg a.i. kg food‑1).  A one generation reproductive study with mallard duck also indicated low toxicity (NOEC 1,000 mg.kg‑1 a.i. respectively). A one generation reproductive study with bobwhite quail indicated some effects on reproductive indices at 300 mg.kg‑1 a.i., but the applicant argued that these effects were not actually treatment related and were not statistically significant in comparison to historical control data (the values of some parameters for control groups in this study being relatively high).  The one generation reproductive study with bobwhite quail was therefore repeated, indicating a NOEC of 615 mg.kg‑1 a.i..

Aquatic toxicity

The determination of aquatic toxicity with this substance was also complicated by its insolubility within the range where it is toxic to several of the species tested.  At concentrations significantly above its solubility, the extent of exposure relative to mean measured tebufenozide concentration is uncertain because of a rapid decline in dissolved tebufenozide content in the first 24 hours of testing and by the presence of undissolved substance.  Some investigators avoided testing at these concentrations and failed to reach toxic concentrations of the substance to the species under test.

Fish

Tebufenozide TGAC was moderately toxic (LC50 > 1, < 10 ppm) from acute (96 hour) exposure to bluegill sunfish (Lepomis macrochirus - LC50 3 ppm) and rainbow trout (Onchorrhynchus mykiss - LC50 5.7 ppm).  As noted above, these results should be treated with caution.  There were no observed effects on sheepshead minnow (Cyprinodon variegatus) with similar acute exposure to mean measured concentrations of tebufenozide up to 0.72 ppm, nor to fathead minnow (Pimephales promelas) with chronic (35 days) exposure to 0.71 ppm.

Daphnia magna and other cladocerans

Tebufenozide TGAC was moderately toxic to Daphnia magna from acute (48 hour) exposure  (EC50 immob , 48 h = 3.8 ppm), but again this result should be treated with caution.  The EC50 immob to D. magna from chronic (21 day exposure) was 0.24 ppm, though daphnid mortality did not commence until the 8th day of exposure at that rate.

Selective toxicity of the substance to cladocerans other than D. magna  (including Bosmina sp., Holopedium sp. and Diaphanosoma sp.) was found in a mesocosm study in a boreal lake under pelagic conditions (2-3 m deep water above an organic, flocculent sediment without vegetation), where initial water concentrations of 0.07-0.66 ppm tebufenozide greatly reduced cladoceran numbers, but did not affect copepod (another Crustacean Order) numbers and increased rotifer (phylum Metazoa) numbers, due presumably to reduced competition.  In that study under pelagic conditions, tebufenozide persisted in the water column at 0.05-0.31 ppm at 35 days after application and 0.02-0.15 ppm at 119 days, and recovery to similar populations to untreated control enclosures took 35-49 days in the 0.07 ppm enclosures, and longer at higher concentrations (> 70 days at 0.33 ppm and > 92 days at 0.66 ppm). 

However, despite these large effects and in the absence of replenishment from external sources, cladoceran populations had essentially recovered one year after application.  The high initial toxicity to cladocerans found in this study contrasts with the low toxicity found in a subsequent study in a boreal lake under littoral conditions (~1.0 m deep water above aquatic vegetation), where there was no evidence of tebufenozide toxicity to cladocerans, copepods or rotifers at concentrations up to 157 ppb (measured one day after application).  A factor which may partially explain the difference in toxicity to cladocerans is the presence of submerged aquatic plants in the littoral situation, providing an adsorbing surface and influencing the dissipation rate of tebufenozide.

Mysid shrimp and oysters

Tebufenozide TGAC was moderately toxic to mysid shrimp (Mysidopsis bahia) from acute (96 hours) exposure (LC50 1.4 ppm), and mysid shrimp were not evidently affected by chronic (28 days) exposure to concentrations up to 0.27 ppm.  Based on shell growth reduction, the substance was highly toxic to Eastern oyster (Crassotrea virginica) from acute (96 hours) exposure (EC50 0.64 ppm).

Aquatic insects

Various laboratory and stream cage tests with aquatic insects in the Orders Ephemoptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), Odonata (dragonflies and damselflies) and Diptera (flies), and a species of Gammarus in the Crustacean Order Amphipoda (freshwater shrimps) indicated no toxicity of tebufenozide (in a formulation similar to one of those proposed) at a nominal concentration of 3.5 ppm. 

There was no evidence of toxicity to various aquatic macroinvertebrates in a simple comparison between two lakes, one treated by aerial application of tebufenozide at a nominal rate of 70 g.ha-1 a.i. and the other unsprayed.  Species present in significant numbers included pill clams (Sphaeriidae), the amphipod Hyallella azteca  and Chironomidae (bloodworms).  Limited data also indicated no effect on Daphnia sp.  However, the concentration of tebufenozide resulting in the treated water was not reported.

Algae

Tests showed that tebufenozide TGAC had high acute (96 hour) toxicity to the freshwater green alga Scenedesmus subspicatus (EC50growth rate 0.21 ppm), but there were no statistically significant observed effects on the freshwater green alga Selenastrum capricornutum at a concentration of 0.64 ppm.  The greater toxicity to Scenedesmus is surprising, given that Selenastrum is usually the more sensitive species (US EPA, 1982c).  A field study in a Canadian lake under pelagic conditions found no effect of initial water concentrations of 0.07-0.66 ppm tebufenozide on chlorophyll a concentration, indicating no overall effect on phytoplankton, and a similar field study under littoral conditions found no adverse effects of tebufenozide (at concentrations of 0.157 ppm one day after application) on phytoplankton abundance.  However the reports of these field studies did not examine effects on the composition of phytoplankton populations.

Toxicity to terrestrial invertebrates

Bees

The majority of the bee toxicity studies provided involved adult bees only, whereas due its mode of action, tebufenozide would be more likely to effect juvenile stages.  However, most of the studies involved observation of effects for at least 72 hours after application, an adequate period to evaluate slow acting toxicity. 

Laboratory tests exposing honey bees to tebufenozide TGAC or 240 SC or 70 W formulations by various routes indicated that it was virtually non-toxic to adult bees (LD50 > 800 g per adult bee by dusting; no significant toxic effects at ~2X field rates or concentrations, with exposure by feeding, vapour, wetting by spray and contact with treated surfaces), and tests also showed that tebufenozide had no repellent effect to adult bees at rates likely to be applied or accumulate in the field. 

A semi-field cage test indicated no effect of tebufenozide on adult bees in bee colonies exposed to tebufenozide spray (concentration 0.012% a.i., rate 262 g.ha-1 a.i., approximately 1.5X the proposed maximum rate for a single spray on pomefruits in Australia), nor on brood mortality or hatched bees.  Field tests also indicated no effects of tebufenozide on adult bee mortality or behaviour from exposure during flight, but gave some indications of adverse effects on pupal mortality and brood development possibly due to tebufenozide application.  The latter effects were not consistently evident, were relatively minor, and were not conclusively shown to be due to tebufenozide treatment. 

It is concluded that tebufenozide applied at field rates is unlikely to affect adult bees.  The information available suggests that the use of tebufenozide is also unlikely to lead to major effects on brood development in nearby hives, but more definitive studies relating particularly to bee larval stages are needed to confirm this.

Predators and parasites

Low toxicity to various insect or mite predators, including larval stages, was demonstrated in laboratory and or field trials.  Tebufenozide treatment in the laboratory at rates well above likely field exposure causing no toxicity to green and brown lacewings (Chrysoperla carnea and Micromus tasmaniae, respectively) or predatory bugs (Podisus  spp., Orius insidiosus).  In Australian field studies, regular application of tebufenozide maintained control of codling moth and LBAM, but led to significantly lower pest mite populations and significantly higher populations of predatory spiders and dimpling bug (Campylomma liebnechti) nymphs compared to azinphos-methyl treatment.  A European laboratory study found no significant effects of tebufenozide at 92 ppm on mortality of the mite predator Stethorus punctum in larval and adult bioassays, and no effect on egg mortality, but a significant reduction in survival of larvae hatched from those eggs.  However, a corresponding field experiment found no significant effects on Stethorus pupal mortality, larval or adult populations, or on mite populations.  There is some evidence (full reports not available for verification by Environment Australia) that the predatory mite species Typhlodromus pyri  was not adversely affected by application of tebufenozide in vine moth trials in Europe.  These results encourage the use of tebufenozide in IPM programs and are evidence of its selectivity within arthropod species.

Detrivors

A study examining the effect of tebufenozide on four species of Collembola (springtails - Folsomia candida, F. nivalis, Onychiurus parvicornis and Hypogastrura pannosa) indigenous to forest soils in Ontario and Quebec found that populations of these detrivor species increased over time in both treated and control microcosms and that tebufenozide did not affect either their survival or reproduction.

Non-target insect pests

A study where tebufenozide was applied topically or orally to various larval stages of a range of pest species indicated that tebufenozide was not toxic to plague locust (Locusta migratoria migratorioides - Orthoptera) or Western corn rootworm (Diabrotica virgifera virgifera - Coleoptera) at the rates tested (up to 100 ppm orally).  In contrast, the LC50 to Lepidoptera larvae was 0.034-0.103 ppm in food for African armyworm (Spodoptera exempta) and 2.5-10.5 ppm for Egyptian cotton earworm (S. exigua).  However, Lepidoptera species did range in sensitivity, topical application LD50 values for the species African armyworm, Egyptian cotton earworm, Egyptian cotton leaf worm (S. littoralis), cabbage moth (Mamestra brassicae) and greater wax moth (Galleria mellonella) being 6.75, 52.9, 11.0, 8.53 and 571 ng.larva-1 respectively.  Tebufenozide was toxic to Colorado potato beetle (Lepinotarsa decemlineata - Coleoptera), but only at high rates: growth and ecdysis were not significantly affected in all instars treated orally at concentrations up to 50 ppm on potato leaves, but tremors, paralysis and death were induced with 100 ppm tebufenozide, egg-laying of 6-day ovipositing females was inhibited by concentrations of 100 or 30 ppm and by topical treatment with 20 g per adult.

Specificity of tebufenozide ecdysteroid activity to Lepidoptera

Ponasterone A and 20E have each been found to have similar binding affinities to dipteran, coleopteran and lepidopteran ecdysteroid receptors, whereas tebufenozide  had very high affinity for lepidopteran ecdysteroid receptors and much lower affinity for dipteran and coleopteran ecdysteroid receptors.  These results are consistent with the above data for whole insect toxicity of tebufenozide, determined in laboratory and field tests.

Earthworms

A study of the toxicity of tebufenozide TGAC to Eisenia foetida found that the 14-day sub-acute LC50 value for this earthworm species is > 1,000 mg.kg-1 a.i. (dry soil), rating tebufenozide as practically nontoxic to earthworms (Mensink et al., 1995).  A microcosm study with the forest litter-dwelling species Dendrobaena octaedra found no significant effects on survival, growth or reproduction of this species in deciduous forest leaf litter treated with up to 0.55 mg.g-1 leaf litter at 70% moisture content (notionally equivalent to the EEC resulting from 7,000 g.ha-1 a.i. contained in the surface 2 cm of litter, i.e. ~6.5X the maximum cumulative annual application under the proposed Australian label).

Endocrine activity

Based on both structure-activity relationships and on a yeast nuclear estrogen receptor assay, tebufenozide is not likely to disrupt endocrine activity, but fully reliable tests for this purpose are yet to be determined.

Toxicity to non-target native plants

Tebufenozide has high crop safety, causing no phytotoxicity to fruit or foliage of apples, pears or grapevines, even at much higher application rates than those proposed on the draft label, and is used on a wide range of plants overseas (including eucalyptus, a proposed use in Brazil), without damage.  Hence native plants are unlikely to be affected if reached by spray.

Toxicity of major metabolites

QSAR modelling indicated that the two major carboxylic acid metabolites (Metabolites 2 and 4) are likely to be significantly less toxic to fish and daphnids than tebufenozide, and this argument is accepted.  The carboxylic acid metabolites are not insecticidally active, while the ketone metabolite (Metabolite 1) has ecdysteroid activity, but significantly less so than tebufenozide.

Environmental Hazard
 

Birds and mammals

Estimated worst case concentrations resulting in a diet exclusively based on feed contaminated by six spray applications at 181 g.ha-1 a.i. are 114 ppm and 42 ppm for quail and mallard duck, respectively.  These concentrations are well below the acute oral, 5-day dietary and one-generation reproduction lowest effect concentrations for these species, hence tebufenozide used in accordance with label recommendations is not likely to present a hazard to birds ingesting these residues.

Similarly, acute or chronic toxicity in mammals is highly unlikely.  The above residues are of similar order to the chronic toxicity no effect concentrations (NOEC's) for mammals, and prolonged consumption solely of material bearing such residues is highly unlikely.

Aquatic organisms
Estimation of EEC

Using US EPA methodology, worst case scenarios can be estimated for a direct overspray on to 15 cm deep lentic water of the formulated product at the maximum label rate (181 g.ha-1 active ingredient).  This results in an estimated environmental concentration (EEC) of 121 g.L-1 tebufenozide.  In the highly unlikely situation that direct contamination occurred at each of six spray applications (the maximum permitted on the draft label), the maximum EEC would be 726 g.L-1 tebufenozide.  The environmental fate studies suggest that initial adsorption to sediment and subsequent dissipation would reduce these concentrations to ≤ 69  g.L-1 tebufenozide and ≤ 350  g.L-1 tebufenozide, respectively. 

A much more likely situation in practical use of this product in orchards and vineyards is contamination of surface waters by spray drift and run-off of material sorbed to soil and organic matter particles.  The US EPA estimates that for pesticides applied by air or mist blower, approximately 10% of the amount sprayed will reach the aquatic environment via spray drift.  Assuming this as a worst case, a maximum EEC of 12.1 g.L-1 tebufenozide would result from a single incident and 72.6 g.L-1 tebufenozide from six repeated incidents, or ≤ 6.9 or 35 g.L-1 tebufenozide, respectively, allowing for adsorption and dissipation. 

These EEC estimates are then related to acute and chronic toxicity data to assess the potential hazard from direct or indirect spray contamination.

Analysis of hazard

Worst case analyses indicate that there is a potential hazard to aquatic invertebrates such as the cladoceran Daphnia magna. and the bivalve mollusc, Eastern oyster (Crassotrea virginica) from a single direct overspray incident or from repeated spraydrift contamination.  Laboratory study results also indicate a potential hazard to the green alga Scenedesmus subspicatus.  However, two Canadian mesocosm studies indicated no overall effects of tebufenozide on phytoplankton.  Therefore toxicity to algae appears unlikely under field conditions, but a potential hazard to certain algal species cannot be ruled out, as these studies did not report population composition.

Evaluation of worst case situations with fish indicate that EEC's are less than 0.1 X acute or chronic LC50 estimates, hence there is no hazard likely to fish, even with repeated direct spray or spraydrift contamination.

There is also no hazard likely to non-lepidopteran aquatic insects or to amphipods, as a study covering aquatic insects in the Orders Ephemoptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), Odonata (dragonflies and damselflies) and Diptera (flies), and a species of Gammarus in the Crustacean Order Amphipoda indicated no toxicity of tebufenozide (in a similar formulation to one of those proposed) at a nominal concentration of 3,500 ppb.  This concentration is greater than the solubility of tebufenozide in water and 4.8X the maximum EEC with repeated direct overspraying.  The hazard to mysid shrimp (Mysidopsis bahia) also appears low, the acute toxicity LC50 being 1,400 ppb and the maximum available NOEC for chronic exposure being 270 ppb.

Mitigating factors

Several factors are likely to reduce the maximum potential environmental concentration of tebufenozide in waterbodies.  It is unlikely that in pomefruit orchards the maximum rate of the product would be used on all six occasions, or that direct overspray or 10% spraydrift would occur on each occasion.  Water depth in waterbodies near orchards or vineyards is likely to exceed 15 cm and is unlikely to be static.  Dissipation of tebufenozide by adsorption and degradation may also be greater than allowed for in these analyses.  In vineyards, the maximum application rate is < 40% of that for pomefruits, and the maximum number of spray applications per annum is three.  Hence the maximum potential EEC values are distinctly lower with vineyard use.

These factors are likely to reduce the maximum EEC sufficiently that no hazard to aquatic organisms is likely from spraydrift, unless it occurs repeatedly to shallow (< 30 cm deep) water, when there is a potential hazard to certain aquatic invertebrates and algae.  Label advice to minimise spraydrift should nonetheless be included to minimise this hazard, or aerial application prohibited.  However, a hazard from even a single direct overspraying incident may remain, hence it is important that direct spray contamination be avoided, and this should be indicated clearly on the label.

Terrestrial invertebrates
Honey bees

Tebufenozide is virtually non-toxic to adult honey bees and is unlikely to exhibit toxicity or have repellent effects on bee foraging at rates likely to be applied or accumulate in the field.  A semi-field cage test indicates that the use of tebufenozide is also unlikely to affect juvenile bee stages, and field tests suggest that effects on brood development are at most relatively minor.  However, more definitive studies would be needed to confirm whether or not juvenile bee stages are affected by this substance.

Other terrestrial invertebrates

Low toxicity to various insect or mite predators, parasites and detrivors was demonstrated in various laboratory and field studies.  These studies, together with the bee and aquatic insect studies and studies with other insect pests, evaluated insects from several Orders and also spiders.  Together with an evaluation of the relative affinity of tebufenozide for ecdysteroid receptors from different species, these laboratory and field toxicity studies indicate that tebufenozide has high selectivity within arthropod species, being highly active against many lepidopterans.  This selectivity encourages the use of tebufenozide in IPM programs.

Tebufenozide has low toxicity to earthworms and is unlikely to cause harm to earthworms in soil reached by spraying.

Conclusions

The submission contains very comprehensive data and the EPA believes that overall, a low hazard to the environment is indicated and that the use of tebufenozide according to label recommendations and good agricultural practice should not result in environmental contamination or acute poisoning of wildlife.

Top

PUBLIC HEALTH AND SAFETY ASSESSMENT

EVALUATION OF TOXICOLOGYY

The toxicological database for tebufenozide which consists primarily of toxicity tests conducted using animals, is quite extensive.  In interpreting the data, it should be noted that toxicity tests generally use doses which are high compared to likely human exposures.  The use of high doses increases the likelihood that potentially significant toxic effects will be identified.  Toxicity tests should also indicate dose levels at which the specific toxic effects are unlikely to occur.  Such dose levels as the No‑Observable‑Effect‑Level (NOEL) are used to develop acceptable limits for dietary or other intakes at which no adverse health effects in humans would be expected.

Toxicokinetics and Metabolism

Tebufenozide is poorly absorbed following oral administration in rats.  It is metabolised by oxidation and cleavage of the t-butyl moiety.  The majority of the dose is excreted in the faeces as parent compound and metabolites within 24 h of dosing, with less than 8% excreted in the urine as metabolites only.  The residue in tissues is low at 7 days after dosing. 

Acute Toxicity

Tebufenozide was of low acute oral toxicity in mice and rats.  No deaths, treatment-related signs of toxicity or gross lesions were observed at 5000 mg/kg.  Dermal toxicity was also low in mice and rats with LD50 values greater than 5000 mg/kg, at which no deaths or signs of systemic toxicity were observed.  Inhalational studies in rats gave an LC50 of approximately 4500 mg/m3 .  Tebufenozide was not a skin or eye irritant in rabbits, nor a skin sensitiser in guinea pigs.

MIMIC 700 WP Insecticide, which contains 700 g/kg tebufenozide, has low acute oral toxicity in rats with an LD50 value of greater than 5000 mg/kg.  The dermal LD50 in rats was greater than 2000 mg/kg.  The inhalational LC50 in rats was greater than 1830 mg/m3 .  No deaths or signs of toxicity were observed in the above acute studies.  The formulation was a slight skin irritant and moderate eye irritant in rabbits, and a slight skin sensitiser in guinea pigs causing a non-typical reaction (red pinpoint foci).

Based on the acute toxicity of tebufenozide and the concentrations of the non‑active constituents of MIMIC 240 SC Insecticide, which contains 240 g/L tebufenozide, the MIMIC 240 SC formulation is expected to be of low oral and dermal toxicity, but a moderate to severe eye irritant and a slight to moderate skin irritant.  MIMIC 240 SC is not expected to be a skin sensitiser. 

Short-term Studies

Rats and rabbits were given tebufenozide by oral gavage at doses of up to 1000 mg/kg/day for 10 and 5 days, respectively.  Rats at 1000 mg/kg/day had higher liver weights than the control animals.  No signs of toxicity were observed in rabbits. 

Short term (2 weeks) dietary administration of tebufenozide resulted in higher liver weights in mice at 350 mg/kg/day and above, anaemia and increased spleen weights in dogs at 20 mg/kg/day and above, increased liver weights in dogs at 75 mg/kg/day and above, and leucocytosis in dogs at 290 mg/kg/day.

Dietary administration of tebufenozide to rats for 2 or 4 weeks resulted in anaemia and increased liver weights at 70 mg/kg and above, increased spleen weights at 210 mg/kg and higher, and decreased feed consumption and body weight gain at 700 mg/kg/day. 

Short term (4 weeks) dermal administration of a formulation, which contains 24% tebufenozide, to rats did not result in systemic toxicity at 1000 mg active ingredient/kg/day.

Subchronic Studies

In a three-month dietary study, male mice had decreased body weight gain at 35 mg/kg/day and above and increased plasma alkaline phosphatase activity at 340 mg/kg/day and above.  Regenerative anaemia, methaemoglobinaemia, neutrophilia, leucocytosis and lymphocytosis were observed in both sexes at 340 mg/kg/day and higher.  The animals receiving 35 mg/kg/day and above had increased haemosiderin deposition and extramedullary haematopoiesis in the spleen, with splenomegaly at 340 mg/kg/day and above.  Increased haemosiderin deposition in the liver and kidney were seen at 340 mg/kg/day and above.  No treatment-related effects were observed in the animals at about 4 mg/kg/day.

In a three-month dietary rat study,  animals receiving 130 mg/kg/day tebufenozide and higher had decreased feed consumption and body weight gain, regenerative anaemia, increased liver weight, and increased pigment deposition in the spleen.  Increased plasma globulin and glucose levels and spleen-body weight ratio, and tubular nephrosis were noted at 1330 mg/kg/day.  No treatment-related effects were seen at 13 mg/kg/day.

In a three-month dietary dog study, regenerative anaemia, methaemoglobinaemia, thrombocytosis, increased liver and spleen weights, increased haemosiderin deposition in the liver and extramedullary haematopoiesis in the spleen were observed in the animals administered 20 mg/kg/day tebufenozide or more.  Plasma bilirubin levels were increased at 20 mg/kg/day and above, and plasma cholesterol levels rose at 195 mg/kg/day.  All the animals at 195 mg/kg/day had bone marrow hyperplasia and some had bilirubinuria at 195 mg/kg/day.  The NOEL was 2 mg/kg/day.

Long‑term Studies

Long-term (18 months) dietary administration of tebufenozide to mice resulted in slight polychromatic anaemia and reticulocytosis at 150 mg/kg/day.  Increased pigment deposition in the spleen and methaemoglobinaemia were observed at 80 mg/kg/day and above.  No treatment-related effects were seen at 8 mg/kg/day.

Rats administered 48 mg/kg/day or more tebufenozide in the diet for 2 years had decreased feed consumption and body weight gain, anaemia, reticulocytosis, and increased haemosiderin deposition in the spleen.  No treatment-related effects were seen at 5 mg/kg/day.

In a long term (one year) dietary dog study, decreased body weight gain, anaemia, reticulocytosis, increased Heinz bodies, increased liver and spleen weights, increased pigmentation in the liver, increased extramedullary haematopoiesis and sinusoidal engorgement in the spleen and bone marrow hyperplasia were observed in the animals administered 9 mg/kg/day or more tebufenozide.  Plasma bilirubin levels were increased from 9 mg/kg/day, and methaemoglobin levels were increased at 54 mg/kg/day.  No treatment-related effects were seen at 1.9 mg/kg/day.

Reproduction and Developmental Studies

In two reproduction studies in rats administered tebufenozide in the diet for two generations, decreased implantations were observed at 150 mg/kg/day.  Fertility was not affected at 14 mg/kg/day.  Parental toxicity was seen at 12 mg/kg/day and above, and included extramedullary haematopoiesis and increased pigment deposition in the spleen, and decreased body weight gain.  There were no toxic effects at 1.8 mg/kg/day.

When pregnant rats or rabbits administered tebufenozide by oral gavage throughout the period of organ formation of the foetus, maternal toxicity including decreased body weight gain and feed consumption was noted in rats at 1000 mg/kg/day.  The rabbits did not exhibit any signs of toxicity at doses of up to 1000 mg/kg/day.  Foetal development was not affected in either species.

Genotoxicity Studies

No evidence of genotoxicity was seen in assays for gene mutation in the Ames test, Escherichia coli or CHO cells in vitro, for chromosomal damage in CHO cells in vitro or rat bone marrow in vivo, and for DNA damage in rat primary hepatocytes in vitro.

Other studies

No evidence of neurological toxicity was observed in rats administered 500 - 2000 mg/kg tebufenozide by single oral gavage.

Top

PUBLIC HEALTH STANDARDS

Poisons Scheduling

The National Drugs and Poisons Schedule Committee (NDPSC) considered the toxicity of the products and active ingredient and assessed the necessary controls to be implemented under States' poisons regulations to prevent the occurrence of poisoning.

The NDPSC recommended that tebufenozide be listed in Schedule 5 of the Standard for the Uniform Scheduling of Drugs and Poisons (SUSDP). There are provisions for appropriate warning statements and first‑aid directions on the product label.

NOEL/ADI

The most sensitive species were rats and dogs with NOELs of about 2 mg/kg/day.  In order to calculate the acceptable daily intake (ADI) for humans, a safety factor is applied to the NOEL in the most sensitive species. The magnitude of the safety factor is selected to account for uncertainties in the extrapolation of animal data to humans; variation within the human population; the quality of the experimental data; and the nature of the potential hazards. Using a safety factor of 100, an ADI of 0.02 mg/kg/day for tebufenozide was established.

Top

RESIDUES IN FOOD AND TRADE ASSESSMENT

Potential For Chemical Residues In Food
 

Background

MimicÒ 240 SC and MimicÒ 700 WP formulations contain tebufenozide as the active ingredient at concentrations of 240 g/Litre and 700 g/Kilogram respectively.  According to the applicant, tebufenozide imitates the natural insect moulting hormone, ecdysone, and works by strongly binding to the ecdysone receptor protein which, when activated, initiates moulting.  When tebufenozide binds to the receptor site, the caterpillar ceases feeding and produces a new but malformed cuticle.  The old cuticle can not be shed and, as a result, the caterpillar is killed by dehydration and starvation.  Caterpillars exposed to sublethal doses of tebufenozide have been observed to emerge as sterile adults. 

The claims for use are for control of light brown apple moth (Epiphyas postvittana) on pome fruit and grapevines, control of pear looper (Chloroclystis spp.) and pear and cherry slug (Caliroa cerasi) on pears and suppression of codling moth (Cydia pomonella) on pome fruit.

Tebufenozide is registered in 16 countries, including New Zealand, Korea, and Japan, for use on pome fruit and or grapes.  An import tolerance for apples has been set in the USA. Residue limits are £1 mg/kg after multiple applications and preharvest intervals of 14 to 45 days in pome fruits and 14 to 30 days in grapes.  The applicant has proposed the following MRLs: Pome fruit 1.0 mg/kg, apple juice 1.0 mg/kg, grapes 1.0 mg/kg, grape juice 0.5 mg/kg, dried grapes 4.0 mg/kg, apple pomace (dry) 1.5 mg/kg and grape pomace (dry) 4.0 mg/kg.  A 28 day withholding period (preharvest interval) has been recommended by the applicant.

To support registration, plant, animal (rat and goat) and poultry metabolism studies, Australian apple, pear and grape residue data from supervised trials, and apple and grape processing studies were presented.  Arguments from the applicant as to why residues in farm animals would not be of consequence were also evaluated. Supplementary New Zealand apple and pear data were also submitted.

Metabolism

Apple, grape, rice, and sugarbeet metabolism studies showed that parent tebufenozide was the major component identified after plant treatment with its rate of metabolism being moderate to slow.  In rat metabolism studies, the majority of the tebufenozide dose was eliminated in the faeces. Liver, kidney, and fat were the sites of highest tissue residues. Measurement of tissue concentrations after dosing indicated clearance of tebufenozide residues from all tissues occurred.  In lactating goats and laying hens, tebufenozide was extensively metabolised with the faeces again containing the majority of administered dose.   In both cases fat was a site of residue deposition. 

Analytical methods and storage stability studies

The analytical methods presented satisfactorily determined tebufenozide in apples, pears, grapes, pomaces and wines. The methods had acceptable recoveries and limits of quantitation. Tebufenozide residue in plant matrices had acceptable stability when appropriately stored.

Residue definition

Because tebufenozide was the significant residue found in the plant metabolism studies and is readily measured by the analytical methodology, the current residue definition of "tebufenozide" remains suitable for plants and plant produce

Residue trials

Australian apple and pear residue data were from high volume spraying trials conducted at rates of 1.6 to twice those proposed for use in Australia. Residues from an Australian apple trial conducted at 9.6 g tebufenozide/100 litres were 1.0 and 1.4 mg/kg 28 days after final treatment. In two Australian trials conducted at 12 g tebufenozide/100 litres, residues were 0.43-1.0 mg/kg 28 days after final treatments.  Although the trial carried out at 9.6 g/100 litres was 1. times the proposed maximum use rate, it was used as the basis of the  recommendation of a temporary  Australian MRL of 0 mg/kg for tebufenozide in apples.  The temporary status was considered appropriate because of general undesirability of having to set MRLs on the basis of trials conducted as rates greater than proposed to be used commercially.

Two Australian pear trials were conducted at 12 g tebufenozide/100 litres, a rate double the proposed high volume label rate.  Twenty-eight days after the last treatment, tebufenozide residues were 0.3, 1.4 and 1.5 mg/kg.  Although these trials were at twice the proposed use rate, they were used as the basis of the recommendation for a temporary Australian MRL of .0 mg/kg for tebufenozide in pears.   The temporary MRL being recommended for the same reason as given for setting a temporary apple MRL.

New Zealand apple and pear residues trials were conducted at 0.5 (pears only), 1, and 2 times the proposed Australian rate.  The residues from the 2x New Zealand apple and pear trials were between 0.15 and 0.41 mg/kg (27-28 day withholding periods) compared to the range of 0.3 to 1.5 mg/kg seen in the comparable Australian trials and it was considered that residues from the New Zealand trials were generally lower than those seen in Australia.  Consequently it was decided that use of the New Zealand residue data from trials conducted at the proposed Australian use rate was inappropriate to establish an Australian MRL for apples and pears.

Because the recommended apple and pear MRLs are the same, it is possible to recommend establishment of a pome fruit MRL of 2.0 mg/kg with a 28 day withholding period.Because the recommended apple and pear MRLs are the same, it is possible to recommend establishment of a temporary pome fruit MRL of 2.0 mg/kg with a 28 day withholding period.

Results of three Australian grape trials using 6 g tebufenozide/100L, the recommended Australian use rate, were reported.  Tebufenozide residues after a 28 day withholding period were 0.32, 0.50, 0.54, 0.60, 0.71 and 1.06 mg/kg.  While the number of applications (5) were greater than the 3 recommended by the proposed use pattern, it was considered that the results supported retention of the current temporary grape MRL of 2.0 mg/kg rather than the 1.0 mg/kg proposed by the applicant. The temporary nature of the MRL was again a consequence of the trial data being generated from a use pattern which was not that proposed by the applicant.

The temporary MRLs recommended are expected to accommodate residues in apples, pears and grapes arising from either the 240 SC or 700 WP formulations when used according to the proposed high volume label rates.

Data to support semi-concentrate spraying of apples or pears were not provided, and in their absence, it was not possible to conclude with certainty  that residues from semi-concentrate spraying of apples or pears would meet an MRL of .0 mg/kg.  In contrast overseas residue data from processing studies on grapes which used concentrate spraying indicated that the proposed semi-concentrate spraying of grape vines should not result in residues exceeding the temporary proposed 2.0 mg/kg grape MRL.  It is also accepted by the APVMA that high volume spraying of grapes to the point of incipient run-off results in maximum residues which can then be used to establish grape MRLs.

Processing studies

An apple processing study showed that the tebufenozide concentration factor in wet apple pomace was 1.5.  Residues were not seen to concentrate in apple juice.  Grape processing studies identified a four-fold concentration of residues in wet grape pomace. Residues were present in some wines made from treated grapes (white wines 0.02 and 0.08 mg/kg, red wines 0.13, 0.14, and 0.26 mg/kg) but there was no concentration observed. Acceptance of argument that the maximum residue concentration of pesticides in going from fresh to dried grapes was four-fold allowed establishment of a temporary dried grape fruit MRL of 8.0 mg/kg.

Animal commodity MRLs

Animal transfer studies were not presented. However the animal metabolism studies indicated tebufenozide in animals was extensively metabolised and a estimation of the maximum expected concentration of tebufenozide residues in cattle fat after feeding of treated grape pomace indicated residues should not exceed 0.05 mg/kg. For these reasons, While no analytical methodology was proposed in the application, and limit of quantitation for such methods are not known, it was decided that animal commodity MRLs need not be were not recommended at this time.

Animal Feed Commodity MRLs

Based on a temporary pome fruitpome fruit MRL of .0 mg/kg, a concentration factor of 1.5 for tebufenozide in wet apple pomace and taking the dry matter content of wet apple pomace as 21%, a temporary  pome fruit a pome fruit pomace, dry MRL of 0 mg/kg is recommended.  Similarly, a temporary grape pomace, dry MRL of 0 mg/kg is recommended based on the temporary proposed grape MRL being of 2.0 mg/kg, the concentration factor in wet grape pomace being 4, and the dry matter content of wet grape pomace being 15%.

Environmental Chemistry and Fate

In soil tebufenozide had estimated half-lives of 33 to 63 days and was not expected to show long-term soil accumulation.  This points to the possibility of tebufenozide residues remaining on forage and soil for some time after treatment.  While grazing of orchards and vineyards may not occur regularly, the persistence of residues points to the need to exclude grazing livestock from tebufenozide treated areas to avoid inadvertent exposure of stock.

Theoretical Maximum Daily intake

The theoretical maximum daily intake of tebufenozide arising from use of the Mimic products on apples, pears, grapes, and oranges would be 5.5 of the proposed acceptable daily intake of  0.02 mg/kg body weight/day.

Trade

The MRLs recommended for pome fruit and grapes are greater than those recommended overseas and it will be necessary to ensure that exported  fruit have tebufenozide residues complying with the MRLs or requirements established by the importing country.  A similar situation exists with dried fruit, especially dried grapes where the temporary Australian MRL recommended is 8 mg/kg.  There is also the possibility that the magnitude of the temporary Australian MRLs  could adversely affect export trade, but this is a direct consequence of the lack of Australian residue data from trials conducted at the proposed use rates. 

Grape processing data indicated that tebufenozide residues can be expected in wine and again it will be necessary to ensure that residue levels in exported wines comply with the requirements of the importing country.

No overseas country is known to have established animal commodity MRLs for tebufenozide at this time.  This should not be a major concern because the extensive metabolism seen in animals and the calculated residue levels in animal commodities point to the low likelihood of measurable residues in animal commodities.

RECOMMENDATIONS - MRLs and Withholding Periods/Restraints

Recommended changes to the MRL Standard are:

Table 1
Compound   Food MRL (mg/kg)
Tebufenozide
DELETE: FP 0226 Apple T2.0
FB 0269   T2.0
ADD: FP 0009 Pome fruits Pome fruits T2.0
DF 0269 Dried grapes T8.0

and

Table 4
Compound Animal Feed Commodity MRL (mg/kg)
ADD:    
Tebufenozide Pome fruit pomace, dry Pome fruit pomace, dry  
  AB 0269 Grape pomace, dry T650

These Table 1 and Table 4 recommended temporary MRLs will be withdrawn from the MRL Standard and a request made to the Australian New Zealand Food Authority to withdraw the relevant entries from Standard A14 on 31 December 1999 unless consideration of any subsequent  application before that date results in a change to the situation.

The residue data and proposed use pattern indicate the following withholding period statements are appropriate:

WITHHOLDING PERIOD

For apples, pears, and grapes:  DO NOT HARVEST FOR 4 WEEKS AFTER APPLICATION

To ensure that grazing or feeding of treated or failed crops does not result in measurable residues in animal commodities: 

DO NOT graze any treated area; or cut for stock food.

Top

OCCUPATIONAL HEALTH AND SAFETY ASSESSMENT

Tebufenozide is not on the National Occupational Health and Safety Commission (NOHSC) List of Designated Hazardous Substances and is determined not to be a hazardous substance by Bayer Australia Limited.

Tebufenozide is an off-white lumpy powder with faint odour.  It has a vapour pressure of 2.67 Pa at 25 0C and is not classified as dangerous goods.  Tebufenozide is of low acute systemic and topical toxicity.  It is manufactured overseas.

Based on available information, Mimic 240 SC Insecticide and Mimic 700 WP Insecticide cannot be determined to be hazardous substances according to the NOHSC criteria.

 Mimic 240 SC Insecticide is an off-white liquid suspension concentrate with slight characteristic smell.  Mimic 700 WP Insecticide is an off-white powder (wettable powder formulation) with a slight musty smell.

Initially both products will be formulated overseas and imported ready to use.  Mimic 240 SC Insecticide will be packaged in 1, 5, 10 and/or 20 litre HDPE containers and Mimic 700 WP Insecticide will be packaged as 86 g water-soluble sachets, with 10 sachets packed in a single outer carton.

Formulation, transport and sale

Tebufenozide products may be formulated in Australia in the future.  In this case, all formulation procedures should be performed in closed vessels under air extraction and chemical testing should be done under fume hoods.  Formulators

and packers should wear appropriate protective equipment such as overalls, gloves, safety boots and eye protection.  Laboratory staff will need to wear laboratory coats, a dust mask and eye protection.

Transport, storage and retail workers could only be exposed to tebufenozide or the products if packaging were breached.  Advice on safe handling of tebufenozide and products during routine formulation and end use is provided in the relevant Material Safety Data Sheet (MSDS).

End use

Mimic 240 SC Insecticide and Mimic 700 WP Insecticide will be used in orchards and vineyards.  Workers can be exposed to the products when opening containers, mixing and loading, spraying, cleaning up spills and equipment and re-entering treated areas.  Both products are diluted in water prior to applying by airblast sprayers and are used at equivalent rates of tebufenozide.  They may be used at high volume and semi-concentrate rates in pome fruits, corresponding to tebufenozide in the working strength spray of 0.006% and 0.018%, respectively.  In grapevines, a maximum of 0.024% tebufenozide is applied.  Both products can be used repeatedly, however for certain apple and pear moths there is a maximum of 6 applications per season.

The primary routes of occupational exposure are via the skin and inhalation of spray mist.  The main acute hazards faced by workers using Mimic 240 SC Insecticide are skin and eye irritation, so workers need protection from spills and splashes with this product.  The main acute hazards faced by workers using Mimic 700 WP Insecticide are skin and eye irritation and skin sensitisation.  However, as the product is contained within water soluble packaging, skin and eye contamination is unlikely.

The following worker exposure studies were submitted by the applicant to Worksafe Australia and used to estimate the risk of health effects following repeated use of the products: 

1.         Hazelton GA and Quinn DL (1992) RH-5992 2F Insecticide: Worker Risk Evaluation for Agricultural Use on Apples and Grapes. Rohm and Haas Report No. 92R-1032, Toxicology Department, Rohm and Haas Company, Spring House, PA 19477.

This comprises the following:

  • Operator exposure derived from the Predictive Operator Exposure Model (POEM)
  • Operator exposure derived from the German BBA Exposure Model
  • Operator exposure using actual field exposure data with a surrogate pesticide, mycobutanil.

2.         Lewis C. (1993): Exposure Assessment and Label Review for Tebufenozide EUP on Walnuts. EPA Reg. No. 707 - EUP-RGR.

Evaluation of these studies, plus supplementary information generated using UK POEM for Australian conditions, indicated that workers needed hand protection when spraying with Mimic 240 SC Insecticide but not with Mimic 700 WP Insecticide.  Airblast sprayers may also breath in spray mist.  However, acute inhalation toxicity is low and the UK POEM estimates that inhalation exposure is small (<0.3%) in relation to skin contamination.  Accordingly, respiratory protection is not needed for sprayers of either product. 

The assessment of worker studies is in Attachment 1.

Entry into treated areas

Given the low acute toxicity and high dilution of applied spray, Worksafe Australia does not recommend a re-entry period at this stage.  The product labels specify a 4-week withholding period before harvest.

Recommendations for safe use

Australian workers involved in formulation or packing of tebufenozide products should be protected by the use of engineering controls, such as, exhaust ventilation and enclosed vessels, by observing safe work practices and by receiving adequate training.  They should wear goggles, gloves, overalls and safety boots.  Testing of chemicals should be done under fume hoods.

End users should follow the instructions and Safety Directions on the product labels.  Safety Directions include the use of personal protective equipment (PPE), namely cotton overalls, elbow-length PVC gloves and face shield or goggles for workers handling Mimic 240 SC Insecticide.  PPE is not needed when using Mimic 700 WP Insecticide.

The PPE recommended should meet the relevant Standards Australia standard specified below:

AS 1337-1992 Eye Protection for Industrial Applications
 

AS/NZS 1715-1994 Selection, Use and Maintenance of Respiratory Protective Devices and AS/NZS 1716-1994 Respiratory Protective Devices

AS 2161-1978 Industrial Safety Gloves and Mittens (Excluding Electrical and Medical Gloves)
 

AS/NZS 2210-1994 Occupational Protective Footwear
 

AS 3765-1990 Clothing for protection against hazardous chemicals

Bayer Australia Limited has produced a MSDS for tebufenozide, Mimic 240 SC Insecticide and Mimic 700 WP Insecticide.  These should contain information relevant to Australian workers, as outlined in the NOHSC National Code of Practice for the Preparation of Material Safety Data Sheets. Employers should obtain these from the supplier and ensure that their employees have ready access to them.

Workers using any hazardous products containing tebufenozide should read the relevant MSDS.

Conclusions

Mimic 240 SC Insecticide and Mimic 700 WP Insecticide can be used safely if handled in accordance with the instructions on the product labels.  Additional information is available on the MSDS for tebufenozide and products.

Top

GLOSSARY OF TERMS

Active constituent   The component of a treatment which is responsible for its biological effect.

Acute toxicity          Immediately measurable effects of a toxin on an organism.

Denatured               Broken down.

Depuration              Cleansing, purification.

Detritus                    Rotting vegetable material.

Diploid                     Having two sets of chromosomes

DNA                         Deoxyribonucleic acid the generic component of the chromosomes which support gene sequences.

Gene                        A length of the DNA which holds the base sequences that code for the formation of a polypeptide chain (protein).

Groundwater

ubiquity score         A measure of whether a compound is likely to leach through soil into groundwater.

IC50                          Inhibition concentration where 50% of (algal) cell growth is inhibited.

IPM                          Integrated Pest Management.  The combination of chemical and biological aspects of pest control to achieve pest management.

LC50                         The concentration of a substance that produces death in 50 per cent of a population of experimental organisms within a specified period.  It is usually expressed as milligrams per litre (mg/L) or milligrams per kilogram (mg/kg) as a concentration in food, water or air.

LD50                                 The dose of a substance that produces death in 50 percent of a population of experimental organisms within a specified period.  It is usually expressed as milligrams per kilogram (mg/kg) of body weight.

Lentic water            Still water.

Photolysis                Breakdown caused by light.

ppm                         Parts per million.

Pomace                    Pulpy residue from apples or other fruit after crushing and pressing

Protease                   Enzymes which break down proteins.

Proteolysis               The process in which proteins chains are lysed (cut) as part of their digestion.

Schedule                  The category into which a chemical is placed according to its human toxicity.

 APPENDIX I

DRAFT LABELS

To protect your privacy, please do not include contact information in your feedback. If you would like a response, please contact us.