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, C1 (15 Spiro-Sel♀ × 15 UNSEL ♂) and C2 (15 Spiro-Sel♂ × 15 UNSEL ♀) O. hyalinipennis was assessed. RESULTS: Spiro-Sel (G21 ) 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 (G28 ) 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, C1 and C2 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. © 2021 Society of Chemical Industry.

Assessment of resistance risk to fipronil and cross resistance to other insecticides in the Musca domestica L. (Diptera: Muscidae).

Fipronil, a phenyl-pyrazole insecticide has been used frequently for the control of disease vector house flies, Musca domestica L., (Diptera: Muscidae) worldwide including Pakistan. This experiment was performed to determine the selection and assessment of fipronil resistance evolution along with cross resistance to other three insecticides. After 26 generations of selection, the house fly strain developed 430-fold resistance to fipronil compared to a susceptible strain. Realized heritability (h(2)) of resistance to fipronil was 0.05. The projected rate of resistance development revealed that if 30-90% house flies were selected then a tenfold increase in lethal concentration 50 happened after 95.51-26.59 generations for fipronil (h(2)=0.05, Slope=2.34). At similar slope, if h(2)=0.15, then 31.84-8.86 generations are required for tenfold increase in LC50 at 30-90% selection intensity, respectively. Likewise, if h(2)=0.25, then similar would occur in 19.10-5.32 generations. Differences in any of the variable would affect the rate of resistance development. Selection with fipronil did not increase the level of resistance to lambda-cyhalothrin, profenofos and indoxacarb, suggesting no cross resistance to these insecticides. The results of our study concluded that house flies have the potential to develop resistances following continued selection pressure with fipronil.