Toxicity of Selected Insecticides Applied to Two Defoliators of Western Hemlock

Abstract

Thirteen insecticides were tested in a laboratory spray chamber on 4th and 5th instar hemlock sawfly, Neodriprion tsugae Middleton. Twelve exceeded DDT in toxicity at both LD50 and LD90. At LD50 the descending order of toxicity to combined groups of 4th and 5th instars was tetrachlorvinphos, resmethrin, fenitrothion, naled, mexacarbate, malathion, pyrethrins, dimethoate, propoxur, carbaryl, methomyl, trichlorfon, and DDT. Of 6 insecticides applied topically to 4th- and 5th-instar western hemlock looper, Lambina fiscellaria lugubrosa (Hulst), 5 exceeded DDT in toxicity at both LD50 and LD90. At LD50 the descending order of toxicity was pyrethrins, phoxim, mexacarbate, Dowco 217 (dimethyl-3,5,6-trichloro-2-pyridyl phosphate), fenitrothion, and DDT.