Effect of post-treatment temperature on toxicity of insecticides to resistant and susceptible house flies.

Abstract

Laboratory and field strains of house flies. Musca domestica L., were treated topically with 1 µliter drops of either diazinon or lindane at various concentrations and held at post-treatment temperatures of 15 and 30°C. With 2 laboratory stains. a diazinon-resistant and a susceptible strain, treated with diazinon. mortality was higher at 30°C. Percent mortality differences between the 2 temperatures at the higher concentrations of diazinon indicated a temperature × diazinon interaction with the resistant strain but not with the susceptible. Mortality of the susceptible strain was similar whether held at 1 temperature for 24 hours or for 8 hours at that temperature plus 16 hours at a higher or lower temperature. Resistant flies held at 30°C for 8 hours plus 15°C for 16 hours showed similar mortality to flies held at 30°C for 24 hours. However, flies held at 15°C for 8 hours plus 16 hours at 30°C also showed a mortality similar to that for flies held for 24 hours at 30°C. With lindane there was significantly higher mortality at 30°C with the susceptible laboratory strain than at 15°C. There was no significant mortality difference between these temperatures with the diazinon-resistant strain. With a third strain, highly resistant to lindane, there was significantly lower mortality at 30°C than at 15°C. Flies collected from several dairy barns and treated topically with diazinon varied significantly in the level of resistance to diazinon, which variation could be correlated with the spray control program which had been conducted in each barn. Percent mortality differences between 15 and 30°C were significantly greater at the higher concentrations of diazinon and were largest with those fly populations showing a relatively high level of resistance.