Negatively correlated cross-resistance to a synthetic pyrethroid in organo-phosphorus-resistant Tetranychus urticae

Abstract

Spider mites are serious pests of food and fibre crops and often cause considerable reductions in yields. Control is usually by regularly spraying chemicals, but frequently this approach has led to the development of resistance to these chemicals and ultimately to reduced levels of control^1–3. A change to another chemical is then necessary. Most species of tetranychid mites of agricultural significance can develop resistance to many organophosphorus insecticides, some organochlorine and carbamate insecticides and various other compounds. Cross-resistance, where resistance to one compound confers resistance to other compounds of the same group, and multiple resistance, where resistance has developed to compounds from a number of structurally different groups, are also known to occur. Occasionally the development of resistance to one compound will have the reverse effect by making a population more susceptible to a newly introduced compound. This effect, termed negatively correlated cross-resistance, could have significant practical advantage in restoring some degree of susceptibility in a pest population. In this letter we describe an example of this phenomenon in spider mites in which resistance to organo-phosphates was linked with increased susceptibility to synthetic pyrethroids.