The cotton aphid, Aphis gossypii G., is a widespread agricultural pest and many populations around the world display resistance to pirimicarb. This resistance originates mainly from acetylcholinesterase modification. Hydrolysis of 14 carbamate and organophosphate insecticides by altered acetylcholinesterase of a resistant strain from southern France has been analyzed. It appeared that the modified enzyme provides a specific resistance to pirimicarb but also a greater sensitivity to bendiocarb. Bioassays showed that the resistant strain was slightly more sensitive to bendiocarb. Utilization of this antiresistance property was tested in the laboratory: a mixed population containing 50% pirimicarb-resistant and 50% pirimicarb-susceptible aphids was established and repetitively treated with bendiocarb. Frequency of resistant individuals in this population was monitored and compared to that of a nontreated mixed population. Treatments with bendiocarb delayed the increase of resistant individuals but as the resistant strain displayed a higher fitness than the sensitive strain and as antiresistance was weak, this selection assay did not allow the population to revert. These data showed that application of this strategy in fields requires compounds displaying high antiresistance properties.