Stability and fitness cost associated with spirotetramat resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae)

BACKGROUND Dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an important pest of cotton and causing economic losses to this crop. It also remains active round the year, infesting a number of host plants. Spirotetramat is a systemic insecticide and is effective against many sucking insect pests. A field collected population of O. hyalinipennis was reared in the laboratory under continuous spirotetramat selection pressure for 21 generations for the development of resistance to spirotetramat. The Spiro-Sel population was further reared for seven generations without insecticide exposure to assess the stability of spirotetramat resistance. Leaf dip method was used for the bioassays and selection. In this study, the impact of spirotetramat resistance on its stability and life history traits of Spiro-Sel, C-1 (15 Spiro-Sel female x 15 UNSEL male) and C-2 (15 Spiro-Sel male x 15 UNSEL female) O. hyalinipennis was assessed. RESULTS Spiro-Sel (G(21)) population developed 2333-fold and 20.83-fold resistance compared with the susceptible and unselected (UNSEL) populations, respectively. Resistance to spirotetramat was unstable after seven generations (G(28)) when reared without exposure to any insecticide. A significant reduction in overall nymphal survival, fecundity, egg hatching and net reproductive rate of Spiro-Sel population was observed when compared with UNSEL population. Intrinsic rate of natural increase, biotic potential and mean relative growth rate were also lower in Spiro-Sel population compared to UNSEL population. The Spiro-Sel, C-1 and C-2 population had a relative fitness of 0.44, 0.51 and 0.44, respectively. CONCLUSION Results of our study suggested that fitness cost is involved in the development of spirotetramat resistance. Unstable resistance and high fitness cost may provide great benefits to limit the evolution of resistance to spirotetramat in O. hyalinipennis.