Spirotetramat Resistance Selected in the Phenacoccus solenopsis (Homoptera: Pseudococcidae): Cross-Resistance Patterns, Stability, and Fitness Costs Analysis.

The Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a major agricultural and horticultural pest of crops throughout the world. To develop a better resistance management strategy for P. solenopsis, we conducted a study on life history parameters of different populations of this pest, one selected with spirotetramat (Spiro-SEL), an unselected (UNSEL) population, and their reciprocal crosses. We also studied the cross-resistance and the stability of spirotetramat resistance. The Spiro-SEL of P. solenopsis exhibited a 328.69-fold resistance compared to the susceptible population (Lab-PK). The Spiro-SEL population also displayed a moderate level of cross-resistance to profenofos and bifenthrin and a high level of cross-resistance to abamectin. Resistance to spirotetramat in Spiro-SEL was unstable in the absence of selection. The study of life history parameters showed that there was a significant reduction in fitness parameters of Spiro-SEL population with a relative fitness value of 0.14. There was a significant decrease in survival rate, pupal weight, fecundity, egg hatching percentage, male and female generation time, intrinsic rate of population increase of males and females, biotic potential, and mean relative growth rate. It is concluded that selection with spirotetramat had marked effect on resistance development in P. solenopsis and upon removal of selection pressure spirotetramat resistance declined significantly, indicating unstable resistance. Development of resistance led to high fitness costs for the spirotetramat-selected population. Our study may provide the basic information on spirotetramat resistance and its mechanism to help develop the resistance management strategies.