Experiments
conducted to study the toxic and biological effects of three chemical
insecticides (chlorpyrifos, Lambda-Cyhalothrin, and Methomyl), one
biochemical insecticide (spinosad), and two bio-insecticides (Bacillus
thuringiensis kurstaki Bt and Nucleopolyhedrovirus, NPV) against neonate
larvae of the pink bollworm, Pectinophora gossypiella (Saund.), were carried out under
laboratory conditions. The highest effect of tested pesticides on larval
mortalities was recorded after four days of feeding these larvae on treated
diet. Spinosad was the effective toxin (LC₅₀=1.84 ppm) to neonate
larvae followed by chlorpyrifos (LC₅₀= 3.06 ppm), Lambda-Cyhalothrin
(LC₅₀= 5.99 ppm) then Methomyl (LC₅₀=23.50 ppm) but B.t.
(74.84×10⁴ I.U) and NPV (83.5×10⁹ I.U) were the lowest
ones. LC₅₀ treatments of neonate larvae with all tested insecticides
produced reduction in larval and pupal weights especially Lambda-cyhalothrin
treatment, (31.9 and 24.3 %, resp.) compared with untreated insects. The
decreasing effect of all treatments observed in fecundity and life span of
adult females which reflected in very high percentages of insect sterility with
chlorpyrifos (66.7%) and Methomyl (61%) treatments. Insignificant increase of
total protein contents and activity of Glutathione-S-transferase enzyme was
detected in tissues of LC₅₀ treated larvae compared with untreated larvae,
but a significant (23.5%) and highly significant (56.9%) increase in enzyme
activity were resulted by Chlorpyrifos and Spinosad treatments. A very high
inhibition in activity of Acetylcholinesterase enzyme of larval tissues was
recorded with NPV (61.3%), B.t. (58.8%), Lambda-Cyhalothrin (55.6%), Spinosad
(54.4%), Chlorpyrifos (48.7%), and Methomyl (37.5%)
treatments than untreated ones.