Risk assessment of cyromazine resistance in a field population of Sesamia inferens (Walker): Cross-resistance, inheritance, and realized heritability

Developing an eco-friendly strategy for pest and resistance management is necessary to enhance agricultural production while protecting the environment. Cyromazine is among biorational insecticides posing very low mammalian toxicity. Resistance to a variety of insecticides has been documented in pink stem borer (PSB) from various regions, especially Pakistan, China and India. In effort to develop a strategy for cyromazine resistance management, trials were done to study toxicity, risk of cross-resistance and resistance development rate. A field population of PSB was collected from the field and exposed to cyromazine. After 20 generations of selection (G2-G21), the RR quickly increased from 29.44- to 115.64-fold. However, the RR dropped to 58.20- fold when Cyro-SEL strain was left unexposed suggesting unstable resistance. The Cyro-SEL strain of PSB showed lack of cross-resistance to all tested insecticides except to lufenuron (very low cross-resistance). Resistance to cyromazine was partly dominant, autosomal, and polygenic in PSB. The value of realized heritability (h(2)) was 0.28 suggesting low potential to develop cyromazine resistance. The projected rate (Pr) of resistance development disclosed that if 95% PSB were selected, then a tenfold increase in LC50 would suggest itself after 4 generations. The findings of our study summarized that PSB has possibility to acquire resistance under permanent selection pressure of cyromazine. The outcomes would be helpful to assist entomologists and growers to manage insecticide resistance in the field.