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The susceptibility to IGRs, moulting hormone agonist, mimic (tebufenozide) and chitin synthesis inhibitors match (lufenuron) was studied in the 2 nd and 4 th larval instars of the cotton leafworm Spodoptera littoralis (Bosid). Obtained results revealed that match was the more toxic against 2 nd larval instars at sub-lethal concentrations LC 25 and LC 50 (0.3 and 0.6 ppm, respectively) than mimic (1.1 and 1.5ppm, respectively). But LC 90 level was the same in the two IGRs. With respect to 4 th larval instar, match induced the higher toxic effect at all sub lethal doses than mimic. Biochemical analysis showed that match and mimic exhibited a severe reduction in the activities of the detoxification enzymes, acid phosphatase and esterases (α and β), as compared to the control. The enzymatic activities were inhibited with the increase in the time posttreatment and also with the increase in dose. Therefore, the tested IGRs, tebufenozide and lufenuron , may be not detoxify by these enzymes.

The present study aimed to evaluate the biological effect of insect growth regulator flufenoxuron (Cascade) as a chitin synthesis inhibitor against 2 nd and 4 th larval instars of Spodoptera littoralis, to determine its toxicity. Effect of sublethal doses LC 25 , LC 50 and LC 90 were used to investigate the enzymatic activities. The tested IGR significantly increased the larval and pupal durations, on the other hand decrease the percentages of pupation, adult emergency, fecundity and fertility of the eggs produced by the adult progeny. The tested compound significantly induced larval mortalities, which were dose dependant.Treatments of the 2 nd and 4 th larval instars with the tested IGR induced some morphogenic abnormalities in larval, larval-pupal and pupal stages, as well as pupal-adult intermediate. Some emerged adults have various degrees of malformations. All the treated larvae as 2 nd instar showed a high sensitivity to the tested IGRs more than 4 th instars. The treated larvae in both 2 nd and 4 th larval instars with the sublethal doses LC 25 , LC 50 and LC 90 showed a significant decrease in enzyme activities of acid phosphatase and the non-specific esterases, α,β esterases at different times intervals post treatments.

No abstract

Six essential oils extracted from garlic (Allium sativum), mint (Mentha piperitaa), basil (Ocimum basilicum), thyme (Thymus vulgaris) , sesame (Sesamum Indicume) and chamomile (Chamaemelum nobile) were tested for both repellency and toxicity against the confused flour beetle, Tribolium confusum adults and last larval instar. Two kinds of repellency bioassays were performed by using filter paper tests and treated kernels. The toxicological bioassay was performed by topical application. The results showed that the tested oils were highly repellent to the adult insect compared to the larvae. By contrast, the toxicological bioassay showed that larvae were more susceptible to tested essential oils than the adults. Effects of essential oils on five detoxification enzymes were also investigated. A reduction in total activities of the major detoxification enzymes in treated larvae was also observed.