Assessing the resistance risk to emamectin benzoate in Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae): selection, cross-resistance dynamics and estimates of realized heritability

Emamectin benzoate, a non-systemic, translaminar, and broad spectrum insecticide, is excessively used in cotton. It kills the pest by suppressing the muscle contraction. Phenacoccus solenopsis Tinsley (Hemiptera: Pseudo-coccidae) is one of the major sap sucking pests of cotton in many countries and has been shown resistance to various insecticides. In this study, we have continuously selected P. solenopsis with emamectin benzoate in the laboratory from G3 to G18 to determine the resistance development and resistance risk to emamectin benzoate and also to evaluate the dynamics of cross-resistance (CR) development with three other insecticides. After continuing selection of P. solenopsis for 16 generations with emamectin benzoate, the emamectin selected strain (Ema-SEL) developed a 280.15-fold resistance when tested at G19. Ema-SEL strain showed no CR to abamectin (0.28-1.65-fold), and profenofos (0.12-0.29-fold), but a very low to low CR to cypermethrin (6.02-11.29-fold). Abamectin was negatively cross-resistant with emamectin benzoate in Ema-SEL strain at G13, G15 and G19 while profenofos also exhibited similar results at G13, G15, G17 and G19. Realized heritability (h2) of resistance to emamectin benzoate was 0.24 from G3 to G19. The results of projected rate of resistance development showed that if h2 = 0.24, 0.34, and 0.44 at slope = 1.08, then 2.03, 1.43, and 1.11 generations, respectively are required for tenfold increase in LC50 at 95 % selection intensity. Results of the present study suggested that P. solenopsis has the ability to develop resistance to emamectin benzoate but it can be managed by the alternate use of other insecticides including abamectin, profenofos and cypermethrin due to lack of/or very low to low CR with these insecticides.

Automated summary

This study found that Phenacoccus solenopsis has developed resistance to emamectin benzoate. However, this resistance can be managed by using alternative insecticides such as abamectin, profenofos, and cypermethrin due to lack of or low cross-resistance.