Effect of Temperature upon the Toxicity of Stomach Poisons

Abstract

Since temp. effects the median lethal concs. of fumigants and contact poisons and, within limits, the higher the temp. the lower the M.L.C., tests were made on 5th-instar larvae of the southern army-worm, Prodenia eridania, and the velvet bean caterpillar, Anticarsia gemmatillis, to find the effect of temp. on the median lethal dose of stomach poisons to lepidopterous larvae. The insecticides were fresh samples of proprietary products including Ca arsenate, acid Pb arsenate, basic Cu arsenate, and synthetic cryolites. With each of these a total of 16 M.L.D.''s were detd. The insects were not fed for 12 hrs. prior to the tests. They were kept in constant-temp. rooms, maintained at the desired temps. (60[degree] and 80[degree]F) throughout the expt. At 60[degree]F Anticarsia larvae were more active than those of Prodenia, but both spp. fed; both were very active and fed well at 80[degree]F. The single leaf method of Hansberry and Richardson as modified by Ellisor and Floyd was used to feed measured doses of the stomach poison to the caterpillars. All insecticides tested were more toxic to Anticarsia than to Prodenia, except basic Cu arsenate. The insecticides were, in all cases except one, more toxic at 60[degree] than at 80[degree] but the mean survival period was shorter at 80[degree].