Fitness cost, cross-resistance, instability and realized heritability of deltamethrin resistance in Tribolium castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) is a common pest of various stored commodities, globally. It is a notorious pest in terms of developing resistance against different insecticides used for its control. In the present study, T. castaneum population was selected with deltamethrin to investigate aspects related to deltamethrin resistance development, such as fitness tradeoff, stability, realized heritability and cross-resistance. After 12 continuous selections, deltamethrin-selected T. castaneum (Delta-Sel strain) developed 49.74-fold and 92.85-fold resistance as compared to field and unselected population, respectively. However, a decrease in level of deltamethrin resistance was observed when selection with deltamethrin was ceased for three generations (G(12) to G(15)), which suggests the unstable nature of deltamethrin resistance. The realized heritability (h(2)) value for deltamethrin resistance was 0.05. The cost paid to develop resistance was observed as reduced fecundity and hatching (%), lower biotic potential, low relative growth rate, and prolonged developmental time, resulting in a decline in the growth potential of the Delta-Sel strain. No cross-resistance to imidacloprid and a very low cross-resistance to chlorpyrifos and bifenthrin was observed. Based on the results, it appears that utilizing insecticides with low or no cross-resistance by interchanging with deltamethrin can be an effective approach for managing resistance and maintaining T. castaneum's susceptibility to deltamethrin. These findings will be helpful for researchers to refine resistance management strategy for delaying resistance and impair survival of T. castaneum.