Abstract
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 LC25 and LC50 (0.3 and 0.6 ppm, respectively) than mimic (1.1 and 1.5ppm, respectively). But LC90 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.
Highlights
Among all cotton pests in Egypt, the cotton leaf worm, Spodoptera littoralis, is the most important
insect growth regulators (IGRs) can be grouped according to their mode of action as: chitin synthesis inhibitors and substances that interfere with the action of insect hormone (i.e. JHa, and ecdysteroids)
The objective of this research was to assess the effect of tested IGRs: moulting hormone agonist, mimic and chitin synthesis inhibitors, benzoylphenylurea derivative, match on the activity of esterases and acid phosphatases of both 2nd and 4th instar larvae of the cotton leafworm S. littoralis (Boisd.) These enzymes were selected as an indicator of insecticide detoxification is based on their importance in the insecticide resistance
Summary
Among all cotton pests in Egypt, the cotton leaf worm, Spodoptera littoralis, is the most important. IGRs differ widely from the commonly used insecticides, as they exert their insecticidal effects through their influence on development, metamorphosis and reproduction of the target insects by disrupting the normal activity of the endocrine system (Oberlander, et al, 1997). Their comprehensive effects and high selectivity as well as lower toxicity to non-target animals and the environment provide new tools for integrated pest management (Huang, et al, 2008).
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