Spinosad resistance in Plutella xylostella and its fitness cost

Abstract

A field strain of Diamondback moth (DBM), Plutela Xylostella was collected from an organic farm in Semenyih, Selangor, Malaysia. The population was reared in glasshouse in UPM and selected with Spinosad until tenth generation (G10). At G10, LC50 for the population is 108.46 ppm as compared to the generations. Fitness cost of the population is low, represented by a value of 0.95 of relative fitness 11.5 ppm of parent (P) generation (Resistance ratio, RR = 9.46), without significant differences among the generations. Fitness cost of the population is low, represented by a value of 0.95 of relative fitness. Survival rate of larva was higher in susceptible strain, larva duration was shortened in the strain and higher adult emergence rate and female ratio was recorded in the strain. The finding suggested that DBM can develop resistance to spinosad in a short time, accompanied by high fitness. Therefore application of spinosad to DBM in the field must be used with precautions in order to delay resistance of the insect to the insecticide.