Detoxification enzymes and the effects of temperature on the toxicity of pyrethroids to the fall armyworm, Spodoptera frugiperda (Lepidoptera:Noctuidae)

1. The effects of temperature on the topical toxicity of cypermethrin and fenvalerate to fifth-instar larvae of the fall annyworm, Spodoptera frugiperda, were investigated, as well as their effects on ataxia and prostration. Activities of carboxylesterase and glutathione S-transferase were also assessed.

2. Pyrethroid toxicities were characterized by a negative temperature coefficient (TC) between 15 and 27°C, and a positive TC between 27 and 38°C. Fenvalerate was more toxic at all test temperatures.

3. The median time for the onset of ataxia and prostration decreased as temperature increased.

4. Activity (μmol/min/mg protein) of carboxylesterase and glutathione S-transferase was significantly lower for fenvalerate-treated insects (217.4 and 17.2, respectively) than for cypermethrin (344.7, 39.7).