The Evaluation of Stomach Poisons for Grasshopper baits

Abstract

Adults of the red-legged grasshopper, Melanoplus femur-rubrum (Deg.) and the differential grasshopper, M. differentialis (Thomas) were fed determined quantities of bran, molasses and water bait which contained known concentrations of arsenious oxide, monosodium arsenite in solution, trisodium arsenite in solution, Paris green, acid lead arsenate, sodium fluosilicate or rotenone. The method is described. The estimated median lethal dose (M.L.D.) of arsenious oxide is 0.36 milligram per gram of body weight. For the sodium arsenites, Paris green and sodium fluosilicate, the M.L.Ds. are approximately equal and estimated to be about 0.16 mg./gram. The M.L.D. for acid lead arsenate is > 3.0 mg./gram and for rotenone probably > 2.0 mg./gram. For survival periods less than 96 hours, monosodium arsenate was more toxic than the other compounds. Under experimental conditions, the grasshoppers were not repelled by the odor or taste of the bait mixtures used, and ceased to feed only when they became satiated or were too sick to eat more. If undisturbed, they usually consumed a toxic dose of an active poison before leaving the bait.