Sublethal effects of NeemAzal (R)-T/S on cockchafers, Melolontha spp. (Col., Scarabaeidae), with a special focus on application timing and beetles' recovery capabilities

摘要

Sublethal effects of NeemAzal (R)-T/S (1 % azadirachtin A) on female cockchafers were studied in two experiments with caged beetles. The beetles were collected in early spring whilst leaving the soil after hibernation. At that time, they had not fed before and they were virgin. The beetles were kept singly in plastic boxes and provided with treated leaves at different stages of egg maturation. The amount of food consumed and the progression of body weight were recorded daily, whereas the state of oogenesis was surveyed at defined intervals. It was shown that food consumption, body weight development and egg maturation were affected by the uptake of azadirachtin-treated plant material compared to beetles from control groups. In no-choice experiments, azadirachtin-treated leaves were accepted readily and feeding was reduced by 60-70 % compared to females fed with untreated foliage. Recovery by feeding on untreated leaves after the uptake of contaminated foliage was either not evident or at a very low level. Moreover, egg maturation was interrupted when females were fed with azadirachtin-treated leaves during the process of oogenesis. If egg maturation was accomplished at the time of first uptake of azadirachtin-treated plant material, caged females were able to lay as many eggs as females from the control group, the egg hatching rate was not affected, and there were no signs of morphological malformations in the freshly hatched L-1-larvae.