Influence of neem oil on detoxication enzyme activity in the obliquebanded leafroller, Choristoneura rosaceana

Larvae of the obliquebanded leafroller, Choristoneura rosaceana L. (Lepidoptera: Tortricidae), were fed artificial diet containing various doses of neem oil. After 6 days of feeding, larvae (6th instar) were assayed for activities of midgut esterases and glutathione transferases. Midgut protein contents were also determined, as were larval fresh and dry weights. Some larvae were allowed to pupate and emerge as adults in order to determine enzyme activities, protein contents, and weights (fresh and dry) of whole adult moths. Neem treatment did not affect the fresh weight of male larvae, although the highest neem dose (0.027%, v/v) significantly reduced the fresh weight of females compared with controls. Dry weights followed the same pattern: no differences in males and reduced dry weight at the highest treatment dose in females. For adult moths, no differences in fresh weight were observed for either males or females. Dry weights were reduced at 0.008% neem in females and 0.010% neem in males. Protein contents were reduced in a dose-dependent manner in male and female larvae and in adult female moths. For glutathione transferase activities, no significant differences were observed with either 3,4-dichloronitrobenzene or 1-chloro-2,4-dinitrobenzene as the test substrate. Although there were some significant differences in rates of 1-chloro-2,4-dinitrobenzene conjugation in adult females, these differences were not dose-dependent. Esterase activities, measured with a-naphthyl acetate and cu-naphthyl butyrate as substrates, were significantly reduced in adult moths (females and males) at all neem treatment doses. Larval esterase activities were similarly reduced at the 0.027% dose. These results indicate that neem oil affects esterase activities but not glutathione transferase activities, and that these effects are most pronounced in adult moths that were exposed to neem as larvae. Neem may be useful in the management of insect populations where insecticide resistance has developed as a result of elevated esterase activity. (C) 1996 Academic Press.