Interaction between short-term heat pretreatment and fipronil on diamondback moth Plutella xylostella (Linnaeus)

The interaction between short-term heat pretreatment and fipronil on 3rd instar larvae of diamondback moth Plutella xylostella (Linnaeus) was investigated. The results indicate that the effect of interaction between short-term heat pretreatment and fipronil on the insects varies with temperature and duration of heat-pretreatment. Heat pretreatment at 30 ℃ for 2 or 4 h can somehow protect insects from fipronil. However, the level of protection is low and unstable as the 30 ℃ pretreatment lasts for 8 h. At 35 ℃, the protection effect is observable in pretreated insects for 2 or 4 h, though 8 h pretreatment improves fipronil toxicity. At 40 ℃, only weak and unstable protection effects are noticeable at 2 h pretreatment duration. Harmful effects develop when the pretreatment is extended to 4 h. Cooperative virulence index (c.f.) may be adopted in Hormesis assessment.