Effects of Abamectin and Milbemycin D on Gypsy Moth (Lepidoptera: Lymantriidae)

Effects of abamectin and milbemycin D on gypsy moth, Lymantria dispar L., were determined. Fifty percent of third instars exposed for 2 h to 5.2 ppm milbemycin D on artificial diet were flaccid and paralyzed, whereas larvae exposed to 5.0 ppm abamectin were unaffected. When larvae were exposed to abamectin on artificial diet for 24 or 48 h, 50% of third instars died. Larvae exposed for 24 h to milbemycin D were not affected, but at 48 h 165 ppm caused 50% mortality of third instars. When larvae were exposed to milbemycin D residues for 48 h and observed 5·d later, the LC50was 92 ppm. LC50’s(ppm) when larvae were exposed for 72 h to residues on poplar foliage were 4 for abamectin, 1,454 for milbemycin D, and 125 for carbaryl. Five days after exposure to foliage residues, LC50’s (ppm) were 1 for abamectin, 244 for milbemycin D and 106 for carbaryl. On both substrates, abamectin was most toxic to third instars. Larvae exposed for 2 h to milbemycin D residues were flaccid and paralyzed but the effect was reversible.