Circadian rhythm in susceptibility of Plutella xylostella tochlorpyrifos and its possible mechanisms

The circadian rhythm in susceptibility of diamondback moth (DBM),Plutella xylostella to chlorpyrifos and the relevant biochemical mechanism were investigated.The susceptibility of DBM to chlorpyrifos changes obviously depends on time of a day and the most sensitive time appears at 10∶ 00 am and 16∶ 00 pm respectively,and the least sensitive time appears at 2∶ 00 am.The biochemical study showed that the changes of specific activity of acetylcholinesterase (AChE),glutathione S-transferases (GSTs) and carboxylesterases (CarE) in P.xylostella were not related to the changes of susceptibility to chlorpyrifos.However the changes may relate to the daily activity habit of P.xylostella.