Physiological and toxicological effects of dible 2X (Bacillus thuringiensis) on the Egyptian cotton leaf worm Spodopteralittoralis (Lepidoptera: Noctuidae).

Bacillus thuringiensis delta-endotoxins are safe biological insecticidal proteins whose usefulness has long been recognized. The insecticidal effect of Diple 2x (Bacillus thuringiensis varkurstaki) was evaluated on 4th instar larvae of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae). The data indicated that, the mortality percentage increased with increasing Dipel 2X concentration. The highest mortality (90%) was obtained by using 4 g/ L of Dipel 2x (5 days post treatment) while 5% mortality was recorded by using 1 and 0.5 g/L compared with the control which recorded no mortality (0%). Died larvae get shrinked and its color turned to dark red compared to the control while survival larvae exhibited several malformations. At the pupae stages changes ranged from dwarf pupa; larvae that fail to pupate (half larvae and half pupa) and the pupa that kept the last instars’ molting skin remaining attached to its body were observed. Also some moth failed to emerge from the pupa cuticle was recorded. B. thuringiensis (Dible 2X) caused a remarkable decrease in amylase, invertase and trehalase enzyme activities compared with the control. The inhibition of carbohydrate hydrolyzing enzymes found in the present study might affect the molting process and subsequently may explain the reason of mortality occurred in S. littoralis larvae.