Selection, cross-resistance, and resistance risk assessment to deltamethrin in laboratory selected Phenacoccus solenopsis (Homoptera: Pseudococcidae)

Phenacoccus solenopsis Tinsley is an invasive and key sucking pest of cotton in particular in India and Pakistan. It has caused huge losses to cotton production and also developed resistance to various insecticides. Deltamethrin is a synthetic pyrethroid used extensively by farmers to control P. solenopsis. This study estimated the risk of resistance development in P. solenopsis against deltamethrin by selecting the population continuously for 23 generations. Cross-resistance to other insecticides (lambda-cyhalothrin, profenofos and acetamiprid) was also determined. Selection of P. solenopsis with deltamethrin from G(3) to G(25) increased the resistance from 38.6-fold to 4632.7-fold compared to a susceptible strain. Selection with deltamethrin did not induce cross-resistance to profenofos but low cross resistance developed against lambda-cyhalothrin and acetamiprid after 23 generations. Realized heritability of deltamethrin resistance was 0.12. A ten-fold increase in deltamethrin resistance required 29 and 3 generations at selection intensities of 10% and 95%, respectively, if h(2) = 0.2 and slope = 1.33. However, with h(2) = 0.1 and slope = 1.33, 48 and 6 generations were needed for a 10-fold increase in deltamethrin resistance at selection intensities of 10 and 95%, respectively. If h(2) = 0.3 and slope = 1.33, the same increase in resistance to deltamethrin will occur after 19 and 2 generations at selection intensities of 10% and 95%, respectively. Our findings show the potential of P. solenopsis populations to develop resistance to deltamethrin. Management strategies such as conservation of natural enemies, appropriate insecticide use and preservation of susceptible populations in the field should be devised to slow down resistance development in P. solenopsis.