Abstract
The cotton mealybug, Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a devastating pest that cause rigorous damage to the number of crops through feeding, managed by using various insecticides. To assess the risk of resistance and design a strategy for resistance management, a field collected population of P. solenopsis was selected with deltamethrin in the laboratory for six generations to investigate the cost to its fitness and to examine cross resistance to different insecticides. Bioassay results at G(8) showed that the deltamethrin selected population (Delta-SEL) developed a resistance ratio of 100-fold compared to that of the unselected population (UNSEL). The deltamethrin resistance population exhibited strong cross-resistance to acetamiprid and lambda-cyhalothrin, but no cross-resistance to profenofos when compared to that of the UNSEL. The relative fitness of the Delta-SEL population was 0.37, with considerably lower survival rates from crawler to second instar, fecundity, hatchability, number of next generation nymphs, net reproductive rate and biotic potential compared with that of the UNSEL. The cost of fitness associated with deltamethrin resistance was evident in the Delta-SEL population. The present study provided useful information for management strategies to overcome development of resistance.