In order to collect basic information for a resistance management program of Aphis gossypii Glover to carbosulfan, studies to evaluate fitness costs associated to this resistance were conducted under laboratory conditions. For this purpose, we studied the stability of carbosulfan resistance in A. gossypii populations with differing initial frequencies of resistance and compared life-history traits of carbosulfan-susceptible and resistant strains. The stability of resistance was followed in

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... populations with initial frequencies of 20, 50 and 80% of resistant individuals. The susceptibility to carbosulfan was monthly estimated by using the diagnostic concentration of 32 ppm. The biology of carbosulfan-susceptible and resistant strains was evaluated in cotton plants kept under controlled climatic conditions. The resistance to carbosulfan was unstable, that is, there was a significant increase in the susceptibility of different populations of A. gossypii to this insecticide in the absence of selection pressure. Comparison of biological traits between carbosulfan-susceptible and resistant strains showed that there is a fitness cost associated with resistance. The resistant strain showed lower fecundity, shorter reproductive period and lower longevity than the susceptible strain. The net reproductive rate (R o ) was 14.04 and 43.18 and the finite rate of increase (λ) was 1.25 and 1.30 females/female/day for the resistant and susceptible strains respectively. Therefore, the instability of carbosulfan resistance in A. gossypii can be exploited in resistance management programs.