Physiopathological studies on bacterial infection of cotton leaf worm Spodoptera littoralis

Abstract

The physiology of the cotton leaf wonn, Spodoptera littoralis (Boisd.) larvae infected with different concentrations of Bacillus thuringiensis var. kurstaki (Dipel-2x) was investigated. Leaf- dipping technique was used to carry out this study and induced the following. The 2nd larval instar demonstrated a highly susceptible level towards the Dipel - 2x, the 3rd and 4'b larval instars exhibited moderate susceptibility while the s•h and 6th larval instars showed relatively very low susceptibility. The larval treatment with different concentrations ofDipel -2x for 48 hrs influenced the reproductive capacity of the tested insects from different aspects: reducing adult emergence, increasing the percentage of different malformation, reducing fecundity, and prolonged the generation period. Pupation increased with decreased the bacterial concentration. Reduction in adult emergence reflects the effect of the toxin on the larvae before pupation. Also, the bacterial infection induced several changes in the haemolymph contents. Highly significant reduction in the protein content as the concentration decreased. Highly significant reduction in the lipid content, the activities of acetylcholinesterase and lactic acid dehydrogenase as the concentration increased. A significant reduction in the activity of acid phosphatase as the concentration increased. A significant increase in the activity of alkaline phosphatase as the concentration increased.