Temperature Relationships in Organophosphorus Poisoning in Boll Weevils12

A laboratory culture or organophosphorus-susceptible boll weevils was exposed at different temperatures to cotton leaves or filter-paper discs previously treated with insecticide or defoliant. All materials examined showed a positive temperature coefficient of toxicity with methyl parathion and malathion being the most toxic at all temperatures. The toxicities of azinphosmethyl and EPN® (O-ethyl O-p-nitrophenyl phenylphosphonothioate) were severely decreased at 10°C while DEF® (S, S, S-tributyl phosphorotrithioate) showed appreciable toxicity only at 32°C. Studies involving different exposure and holding temperatures indicated that a higher exposure temperature results in increased toxicity, even though the holding temperature is the same for all treatments. Although transferring the insects to a low holding temperature from a high exposure temperature decreased the effectiveness of the toxicant, the corrected mortality of the insects exposed at 32°C and held at 10°C was more than twice that of those exposed and held at 10°C. These data suggest that temperature may affect both the innate toxicity and the rate of absorption of the insecticide into the insect.