Insect Physiology Research Laboratory, Section of Entomology, Department of Zoology, Aligarh Muslim University, Aligarh-202 002, Uttar Pradesh, (India).
The sublethal levels of cythion (malathion) at the concentrations of 10, 20, 40, 60 and 80 ppm/4th instar nymph of Dysdercus koenigii resulted in concentration-based changes. The nymphal loss and survival duration of the treated insects were directly proportional and increased linearly with the increase in concentration. On the other hand, the fecundity and fertility of the adults, emerged from the treated nymphs were inversely proportional, decreased linearly and showed negative correlation with concentrations. The initial mortality following the topical application of higher concentrations (i.e. 80, 60 and 40 ppm) was very high within 24 hours. However, the subsequent mortality up to adult emergence was insignificant. Out of the total adults that emerged from the treated nymphs, few were with malformed wings and legs. The lower concentrations (i.e. 20 and 10 ppm) had negligible effect and were well tolerated. The treatment of insects with the highest concentration (i.e. 80 ppm) resulted in gradual degeneration of oocytes, which ended up in total dissolution of the ovarian follicles where all the follicular individualities were lost in a homogenous degenerative ovarian mass. One or two gigantic eggs were developed, but at no time any of these eggs could continue successful growth. Eventually all the oocytes degenerated completely. However, the lower concentrations had negligible effects on the gonads.
