LAUSR

Abstract Spinosad is new chemical insecticide, which acts on nicotinic acetylcholine receptor. Selection of Phenacoccus solenopsis with spinosad was carried out in the laboratory to characterize spinosad resistance. Cross resistance, stability and fitness cost of spinosad resistance were evaluated. Phenacoccus solenopsis showed a 282.45-fold resistance to spinosad after seven rounds of selection. Spinosad selected population (Spinosad-SEL pop) showed different levels of cross-resistance to profenofos, spinetoram and deltamethrin in comparison with unselected population. Spinosad resistance decreased significantly from 282.45 to 25.4-fold when resistant population was not exposed to the insecticide for up to six generations, indicating unstable resistance. Relative fitness of Spinosad-SEL pop was 0.51 with decrease in survival rate, fecundity, intrinsic rate of male and female, biotic potential and mean relative growth rate of male, whereas prolonged developmental time from egg to adult male and female, and generation time of both sexes compared with the unselected population. Resistance to spinosad indicates the need to rotate insecticides with others of differing modes of action and implementing alternative methods for P. solenopsis management.