Diflubenzuron metabolism

Diflubenzuron (Dimilin , TH-6040) is an IGR which inhibits the normal deposition of chitin. The metabolic fate of diflubenzuron has been studied in sheep U, 2), cattle (1 ), rats (1, 3), house flies (4, 5), stable flies (5), chickens (6), swine (6), boll weevils (7), plants (8 9), and soil (2, 8, 10). Since good reviews of diflubenzuron metabolism have been given by Ivie (11) and Verloop and Ferrell (9), we will present only a tabular summary of the degradation of diflubenzuron in nonaguatic systems for comparative purposes (Table I). The remaining discussion will focus on diflubenzuron degradation in the aquatic environment. 

Diflubenzuron can be either hydrolyzed at the urea bridge or oxidized by ring hydrox-ylation followed by conjugation. Hydrolytic cleavage seems to be a major route for diflubenzuron metabolism in many insect species. Two-spotted spider mites showed <10% absorption in 96 h of topically applied diflubenzuron. Of the amount absorbed, about 27% was metabolized in 96 h to 4-chlorophenyl urea, 2,6-difluorobenzoic acid, 4-chloroformanilide, 2,6-difluorobenzamide, and other metabolites. Effects of diflubenzuron were synergized by profenofos in cotton leafworm fourth instar larvae, and they were antagonized by 20-hydroxyecdysone in beetle (Tenebrio molitor) pupae. More information is needed on interaction effects of diflubenzuron with other chemicals. 

Many pesticides cause endocrine disruption in vertebrate and invertebrate species at concentrations that are not overtly metabolically toxic. The insect growth inhibitor diflubenzuron can affect the reproduction, development and behaviour of estuarine crustaceans at concentrations of just lOmgP (reviewed... 

Diflubenzuron breakdown by hydrolysis, soil degradation, or plant and animal metabolism initially yields 2,6-difluorobenzoic acid and 4-chlorophenylurea. Ultimately, the end products are... 

Foliage of cotton that initially contained 100 mg/kg DW contained about 60 mg/kg after 7 weeks leaf residues consisted entirely of the parent diflubenzuron (Gartrell 1981). Diflubenzuron applied topically to lima bean (Phaseolus lunatus) foliage was not absorbed by the plant, as expected. Injected diflubenzuron, however, was metabolized, and certain metabolites were similar to those isolated from mites (Franklin and Knowles 1981). 

Oral treatment of sheep and cattle (Bos spp.) with diflubenzuron is followed by absorption of the compound through the gastrointestinal tract, metabolism, and elimination of residues through the urine, feces, and, to a very limited extent, milk. Intact diflubenzuron is eliminated in the feces of orally dosed cattle and sheep (Ivie 1978). Major metabolites of diflubenzuron excreted by cattle and sheep result from hydroxylation on the difluorobenzoyl and chlorophenyl rings, and by cleavage between the carbonyl and amide groups to produce metabolites that are excreted free or as conjugates (Ivie 1978). Cattle dosed repeatedly with diflubenzuron had detectable residues only in liver... 

Birds seem comparatively resistant to diflubenzuron acute oral LD50 doses exceed 2000 mg/kg body weight (BW) dietary concentrations <4640 mg/kg FW are tolerated for at least 8 days and forest birds seem unharmed by recommended diflubenzuron application procedures to control pestiferous insects, except for a possible loss in fat reserves. Intraspecies differences in ability to metabolize diflubenzuron are probably large different strains of domestic chickens show significant differences in ability to accumulate and retain this compound. 

Franklin, E.J. and C.O. Knowles. 1981. Metabolism of diflubenzuron by spider mites and bean plants. Pestic. Sci. 12 133-141. 

Jenkins, V.K., R.R. Perry, A.E. Ahmed, and K. Ives. 1986. Role of metabolism in effects of diflubenzuron on growth of B16 melanomas in mice. Investig. New Drugs 4 325-335. 

Opdycke, J.C., R.W. Miller, and R.E. Menzer. 1982a. Metabolism and fate of diflubenzuron in swine. Jour. Agricul. Food Chem. 30 1223-1227. 

Microorganisms. Diflubenzuron was stable to degradation by uncharacterized microorganisms from a sewage lagoon (12). Pseudomonas putida (soil microbe) also was unable to metabolize ... 

Plectonema boryanum, were voracious degraders of diflubenzuron (Table III). Just 5 mg of algae cells could metabolize almost 80% of the applied diflubenzuron in just 1 hr. Curiously, this pace was not sustained since 45 mg of algae could degrade only 95% of the applied dose after four days. 

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