The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn(Homoptera : Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC5 0 of 0.003 mg litre(-1) and against nymphs at 0.02 mg litre(-1). In compari son, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and n ymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an I sraeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than p yriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriprox yfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effec t on the toxicity of fenoxycarb. Collectively, these data imply that the mo des of action of pyriproxyfen and fenoxycarb are distinct, despite the stru ctural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. (C) 1999 Society of Chemical Ind ustry.