Field-based assessment of insecticide resistance, cross-resistance, and resistance risk mapping (RRM) in the legume pod borer, <i>Maruca vitrata</i> F.

The legume pod borer, <i>Maruca vitrata</i> F., is a pantropical insect pest causing substantial yield losses in legume crops. The larvae cause significant damage to crops like cowpea, beans, and pigeon pea. Intensive and indiscriminate use of insecticides is practised by legume growers across the world. The field control failures owing to the development of insecticide resistance were suspected in Indian populations of <i>M. vitrata</i>. Hence, the present study investigated the development of insecticide resistance in five field-collected populations of <i>M. vitrata</i>, collected from the Southern states of India. Dose-mortality bioassays indicated varying levels of insecticide resistance across populations as compared to the insecticide-susceptible laboratory-reared population. The estimated resistance ratios were as follows: 30.96- to 81.85-fold for lambda-cyhalothrin, 10.85- to 38.91-fold for emamectin benzoate, 12.02- to 48.55-fold for broflanilide, 8.42- to 54.89-fold for spinosad, and 19.46- to 28.37-fold for indoxacarb. Significant positive correlation was observed between emamectin benzoate and spinosad susceptibility, suggesting potential cross-resistance. These findings highlight the development of insecticide resistance in <i>M. vitrata</i> and underline the need for region-specific resistance management strategies, including insecticide rotation with non-cross-resistant compounds, to ensure sustainable insect pest control.