INSECT RESISTANCE MANAGEMENT IN BT CROPS: FROM HIGH-DOSE/REFUGE STRATEGIES TO TOXIN DIVERSIFICATION AND MOLECULAR MONITORING

Abstract

Bt crops have provided effective control of several important insect pests and reduced dependence on chemical insecticides, but their continued use has imposed strong selection pressure for resistance. This review examines major approaches for managing resistance to Bt crops, beginning with the high-dose/refuge strategy and extending to toxin diversification and molecular monitoring. The high-dose/refuge strategy has delayed resistance in several pest species, but its effectiveness can be reduced by inadequate toxin expression, non-recessive resistance, limited refuge compliance, and non-random mating. Gene pyramiding can improve durability when component toxins act independently and are expressed at effective levels, whereas cross-resistance can reduce its benefits. Modified Cry toxins, structurally unrelated Cry, Cyt and Vip proteins, and the exploitation of negative cross-resistance provide additional options for overcoming resistance. Non-Bt traits, including protease inhibitors and lectins, can further diversify insecticidal mechanisms. RNA interference offers a mechanistically distinct approach and has progressed to commercial use, while CRISPR/Cas9-based strategies show potential through modification of plant defense and metabolic pathways. Finally, DNA-based and genomic methods can improve early detection of resistance alleles. Overall, durable resistance management requires integration of mechanistically distinct control tactics with appropriate refuges and continuous resistance monitoring, supported by field-scale validation.