The susceptibility to IGRs, moulting hormone agonist, mimic (tebufenozide) and
chitin synthesis inhibitors match (lufenuron) was studied in the 2nd and 4th larval instars
of the cotton leafworm Spodoptera littoralis (Bosid). Obtained results revealed that
match was the more toxic against 2nd 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 4th 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.