Laboratory studies on the behavioral responses of Tribolium confusum and Ephestia kuehniella to surfaces treated with diatomaceous earth and spinosad formulations

Abstract

Laboratory bioassays were conducted to determine the behavioral responses of adults and larvae of Tribolium confusum Jacquelin du Val and larvae of Ephestia kuehniella Zeller to surfaces treated with two diatomaceous earth (DE) (Insecto, SilicoSec^®) and one spinosad formulations, applied alone or in combinations. Five series of bioassays were carried out by using petri dishes with their bottoms separated into two equal parts. The dishes contained different treatments of combinations of the DE or spinosad formulations or one part left untreated. After the preparation of the treatments, ten insects were released in the center of the dish and observations were taken for 60 min at 5-min intervals. In general, the released insects showed positive preference upon contact to the DE-treated wheat as compared with the untreated substrate. There was no negative preference upon contact to the presence of DEs, with very few exceptions. Interestingly, a strong positive preference upon contact was observed for the spinosad formulation. When the tested DEs were applied in combination with spinosad, the presence of spinosad generally negatively affected the preference upon contact, especially in the case of larvae. The results of the present work indicate specific behavioral responses of stored-product insects to insecticidal formulations, which can strongly affect the efficacy of control strategies and should be taken into account.