Monitoring, inheritance and stability of insecticide resistance in Oxycarenus hyalinipennis (Hemiptera: Lygaidae) from Southern Punjab, Pakistan

Abstract

Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is a sucking pest of many host plants and has become severe sucking pest of cotton in Pakistan by causing quantitative and qualitative losses. Resistance levels to pyrethroids such as bifenthrin, deltamethrin, and lambda-cyhalothrin were medium, tolerance to low resistance, and tolerance to low resistance to medium, respectively compared with Lab-PK. The organophosphate insecticides profenofos and triazophos exhibited medium and tolerance to low resistance to medium, respectively compared with Lab-PK. Five novel chemistry insecticides showed the RR in range of tolerance to low resistance against emamectin benzoate, tolerance to low resistance to medium in spinosad, medium to high in chlorfenapyr, medium in imidacloprid and tolerance to low resistance to medium in nitenpyram. Genetic basis of chlorfenapyr resistance in O. hyalinipennis were also explored by selecting the population for continuous six generations. The selection resulted in 149.06 fold resistance in O. hyalinipennis. Chlorfenapyr resistance in O. hyalinipennis was autosomal, incompletely dominant and polygenic. Synergism bioassays with PBO and DEF revealed chlorfenapyr resistance might be due to esterase activity. To determine if synergism occurs between organophosphate, pyrethroid, carbamate and new chemical insecticides, representative compounds of these groups were tested (cypermethrin, chlorpyrifos, methomyl, acetamiprid, fipronil and spirotetramat) in a 1:1 and LC50:LC50 ratio against O. hyalinipennis. Cypermethrin combined with methomyl and spirotetramat, methomyl with spirotetramat, acetamiprid with spirotetramat and fipronil with spirotetramat had synergistic effects (CI ˂ 1) in a Lab-PK. Methomyl combined with acetamiprid and acetamiprid with fipronil had synergistic effects on a Field-POP. Cypermethrin combined with methomyl and spirotetramat, chlorpyrifos with methomyl, acetamiprid and spirotetramat, methomyl with acetamiprid and spirotetramat and fipronil with spirotetramat also had synergistic effects on a Field-POP. Enzyme inhibitors PBO and DEF significantly increased the toxicity of chlorpyrifos, methomyl, acetamiprid and spirotetramat to a Field-POP, suggesting a monooxygenase and esterase based resistance mechanisms. However fipronil did not synergise with PBO and DEF. Stability and cross-resistance in a laboratory selected field strain of O. hyalinipennis were also studied. The Chlorfenapyr-SEL population (149.06-fold) showed limited cross-resistance to bifenthrin, triazophos, fipronil, and emamectin benzoate. Resistance to chlorfenapyr was also unstable as a result of removal of selection pressure for further five generations. The toxicity of chlorfenapyr was significantly greater compared to bifenthrin when tested on a field population (Field-POP) and an unselected population (UNSEL-POP) whereas the toxicity of chlorfenapyr was significantly lower than that of triazophos when tested on a chlorfenapyr selected population at generation 7. Chlorfenapyr toxicity was statistically similar to bifenthrin, triazophos, fipronil and emamectin benzoate when tested on Field-POP, UNSEL-POP and Chlorfenapyr-SEL (G7). A field population of O. hyalinipennis from Punjab, Pakistan showed medium resistance to chlorfenapyr, bifenthrin, triazophos but tolerance to low resistance was found against fipronil and emamectin benzoate, compared with the Lab-PK population. Regular assessment of resistance to insecticides and integrated management plans like judicious use of insecticides and rotation of insecticides along with different modes of action are required to delay resistance development in O. hyalinipennis.