Inheritance and Fitness Costs of Laboratory-Selected Cry1Ab Resistance in Ostrinia furnacalis

The Asian corn borer, Ostrinia furnacalis, is a major pest in China and across East and Southeast Asia, serving as the primary target of Bt maize expressing Cry proteins. Evolution of resistance to Bt toxins represents a critical challenge in plant protection. The high-dose/refuge strategy is more effective when resistance is recessively inherited and fitness costs are present. Here, we characterize the inheritance pattern and fitness costs of Cry1Ab resistance in O. furnacalis using a resistant strain exhibiting a resistance ratio of >1400-fold. The LC50 values of F1 hybrids from reciprocal crosses between resistant and susceptible strains were 2.44 (1.90–3.12) μg/g and 2.01 (1.53–2.61) μg/g, respectively, with no significant difference, indicating autosomal inheritance. The effective dominance (h) of F1 offspring decreased with increasing concentration, suggesting that resistance was concentration-dependent. Analysis of observed versus expected mortality in backcross progeny (F1 × resistant strain) indicated that Cry1Ab resistance is likely governed by more than one genetic locus. Compared with the susceptible strain, resistant individuals exhibited prolonged larval development (18.6 d vs. 17.2 d, p < 0.001), reduced pupation (42.5% vs. 60.8%, p < 0.001) and adult emergence rates (60.3% vs. 87.8%, p < 0.001), while fecundity was not significantly affected. These results verify the existence of fitness costs associated with Bt resistance. Our findings provide important insights into the mechanistic basis of Cry1Ab resistance and will assist in designing proactive management strategies to delay resistance evolution in field populations of O. furnacalis.