Insecticide Susceptibility and Response to Selected Pollens of Larval Alfalfa Leafcutting Bees,Megachile pacifica(Panzer) (Hymenoptera: Megachilidae)1

A method for rearing larvae from field-collected eggs of Megachile pacifica (Panzer) was used to measure insecticide toxicities, synergist ratios, and larval growth on 4 pollen species. Carbaryl, propoxur, Landrin® (3,4,5-trimethylphenyl methylcarbamate and 2,3,5-trimethylphenyl carbamate) and methomyl had LC 50 values ranging from 42–121 ppm. Gardona® [2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate] and monocrotophos were more toxic with LC 50 values of about 1.7 and 2.6 ppm, respectively. The carbaryl-piperonyl butoxide synergist ratios for the larvae were estimated to range between 1.57–2.17. Alfalfa pollen provided the best larval growth. Pollens from goatsrue, sweet clover, and goldenweed were less satisfactory.