Interaction between short-term heat pretreatment and avermectin on 2nd instar larvae of diamondback moth, Plutella xylostella (Linn).

Based on the cooperative virulence index (c.f.), the interaction effect between short-term heat pretreatment and avermectin on 2(nd) instar larvae of diamondback moth (DBM), Plutella xylostella (Linnaeus), was assessed. The results suggested that the interaction results between short-term heat pretreatment and avermectin on the tested insects varied with temperature level as well as its duration and avermectin concentration. Interaction between heat pretreatment at 30 degrees C and avermectin mainly resulted in addition. Meanwhile, pretreatment at 35 degrees C for 2 or 4 h could antagonize the toxicity of avermectin at lower concentrations, which indicated a hormetic effect occurred. The results indicate that cooperative virulence index (c.f.) may be adopted in hormetic effect assessment.