Detoxification of diflubenzuron and teflubenzuron in the larvae of the beet armyworm ( Spodoptera exigua) (lepidoptera: Noctuidae)

Abstract

The predominant pathway for diflubenzuron and teflubenzuron detoxification in fifth instar larvae of Spodoptera exigua was studied. The insect showed a high tolerance against diflubenzuron and teflubenzuron, and a relatively high susceptibility to chlorfluazuron and hexaflumuron. According to LC 50 values, chlorfluazuron (0.093 mg/liter) and hexaflumuron (0.053 mg/liter) were considerably more potent than diflubenzuron (15.79 mg/liter) and teflubenzuron (7.30 mg/liter). Profenofos and diethyl maleate synergized both diflubenzuron and teflubenzuron, indicating that the major route of detoxification in S. exigua was through hydrolysis and conjugation. Limited synergism by piperonyl butoxide indicated that mixed function oxidase enzymes play a minor role in benzoylphenylurea (BPU) detoxification. A metabolic study in function of time was carried out. A large part of the less potent benzoylphenylureas was rapidly excreted. An excretion of 67% of diflubenzuron and teflubenzuron was detected 12 hr after intake. The remaining part of diflubenzuron was mostly hydrolyzed to 4-chlorophenylurea and 4-chloroaniline (62% of the metabolites) confirming the conclusions of the synergism study. In addition to hydrolysis, conjugation plays an important role in the detoxification of teflubenzuron (45% of the metabolism). The in vivo metabolism of diflubenzuron and teflubenzuron could be reduced by 50 and 30%, respectively, using sublethal concentration of profenofos and by 35 and 40%, respectively, using diethyl maleate.