Co-Authors:
Ishaaya, I., Department of Entomology, ARO, The Volcani Center, Bet Dagan 50-250, Israel
Degheele, D., Faculty of Agricultural Sciences, State University of Ghent, Coupure Links 653, B-9000 Ghent, Belgium
Abstract:
Optimal assay conditions for gut diflubenzuron (DFB) hydrolase(s) of the Egyptian cotton leaf worm Spodoptera littoralis larvae are 0.9 mg protein of the postmitochondrial supernatant fraction incubated for 2 hr at 37°C with 0.5 nmol [14C]DFB (uniformally labeled on the aniline ring) in 0.4 ml of 0.05 M glycine-NaOH buffer (pH 9.0). The radiolabeled metabolites are separated and quantitatively evaluated using a TLC procedure. DFB hydrolase activity is a major factor for DFB detoxification in S. littoralis larvae. This conclusion is based on the ability of the larval gut enzyme to hydrolyze DFB to 4-chloroaniline (4-CA) and 4-chlorophenylurea (4-CPU), 4-CA being a major metabolite with a level of about 10% and 4-CPU a minor one with a level of about 1% of the total recovery. A relatively high level of radiolabeled polar metabolites is observed at the origin of the TLC plate; these metabolites are considered to be conjugated materials. DFB hydrolysis is totally inhibited in vitro at a concentration of 10-5 M of profenofos or DEF, which are both considered typical esterase inhibitors. Over 90% inhibition of DFB hydrolase activity in vivo is obtained when larvae are fed with castor bean leaves treated with 2.4 × 10-4% profenofos. Addition of sublethal concentrations of profenofos to dietary DFB resulted in a considerably higher toxicity of the latter. © 1988.
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