Transgenerational effects of sublethal deltamethrin exposure on development and repellency behaviour in Callosobruchus chinensis

Callosobruchus chinensis, belongs to the Chrysomelidae family, is a major pest of pulse grains. It causes 60% weight loss of the pulses, making them inappropriate for planting or human consumption. C. chinensis is commonly controlled with insecticides; however, these insecticides have negative effects on the environment and non-target organisms. Moreover, repeated exposure to the insecticide causes the resistance in the C. chinensis. Initially the lethal concentration of deltamethrin (LC₅₀) was obtained by the probit analysis. Later the study aimed to examine the impact of a sublethal concentration of deltamethrin on various developmental characteristics and repellency behaviour throughout six successive generations of the C. chinensis. For that, two concentration were selected viz sublethal low concentration (1/20^th) and sublethal high concentration (1/5^th) of the LC₅₀ compared to control. Both concentrations significantly reduce the life table parameters like egg count, total hatching, total development duration, total emergence and adult longevity in the first generation but an increasing trend in all the parameters was observed in subsequent generations (progeny). Additionally, the repellency was maximum in 1^st generation but it decreases with the exposure time and successive generations which shows that it was time and generation dependent. The findings indicate that although there are predominantly adverse effects within the generation, exposure to deltamethrin at sublethal levels over the generations can lead to beneficial effects in the offspring, enhancing their ability to withstand insecticides.