Disruptive Effects of Selected Chitin Synthesis Inhibitors on Cotton Leaf Worm Spodoptera littoralis (Boisd.)

Abstract

Spodoptera littoralis is one of the most devastating pests of cotton and other vegetables in Egypt as well as Mediterranean and middle east countries. Chitin synthesis inhibitors (CSIs) are quite distinctive in their mode of action and potentially act on the target species. The susceptibility of laboratory 2nd&4th instar larvae of cotton leafworm Spodoptera littoralis (Boisd.) to CSIs (Flufenoxuron, Chlorfluazuron and Triflumuron) was evaluated. The biochemical responses of S. littoralis larvae was detected using the lc50 of each compound. Flufenoxuron exhibited high level of toxicity with low LC50 value (0.069 ppm) followed by Chlorfluazuron (1.95 ppm) and then triflumuron (75.28) for the 2nd instar larvae while, the lc50 was (0.14 ppm) for flufenoxuron followed by 0.42 ppm for chlorfluazuron and then 1661.58 ppm for triflumuron with 4thinstar larvae. Second instar was more susceptible than the older ones except with chlorfluazuron the 4th instar more susceptible than the 2nd instar. Those CSIs exhibited variations of activities for each enzyme. Both of them increased the activity of AST (Aspartate Transaminase) on the contrary they decreased the activity of ALT (Alanine Transaminase). Flufenoxuron increased the activity of both alkaline phosphatase, alpha & beta esterases, chitinase and phenol oxidase, while it decreased the activity of acid phosphatase. Chlorfluazuron increased the activity of both alpha & beta esterases, chitinase and phenol oxidase, while it decreased the activity of both acid & alkaline phosphatases. Triflumuron increased the activity of both alpha esterase, acid phosphatase, chitinase and phenol oxidase, while it decreased the activity of both beta esterase and alkaline phosphatase. So, from this study, it can be concluded that the overall effects of CSIs use, including mortality and sublethal effects in insects, can facilitate the development of truly selective insecticides that can be employed in integrated pest management strategies.