Laboratory Tests of 55 Insecticides on Douglas-Fir Tussock Moth Larvae1

Fifty-five insecticides were tested for their toxicity to larvae of the Douglas-fir tussock moth, Hemercampa pseudotsugata McDunnough. The 10 most active insecticides in descending order of average toxicity at LD90 were: pyrethrins, Dursban® (O, O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate), Zectran® (4-dimethylamino-3,5-xylyl methylcarbamate), dichlorvos, GC-6506 (dimethyl p-(methythio) phenyl phosphate), aminocarb, tetramethrin, allethrin, Bayer 37298 (O-ethyl 0-2,4,5-trichlorophenyl ethylphosphonothioate), and DDT. Four of the 10 insecticides–pyrethrins, Dursban, Zectran. And DDT–have been field-tested recently with varying results. Several insecticides were examined in the laboratory in more detail in different formulations for such characteristics as rate of toxic action and residual activity.