Resistance Evolution To Bt Toxins Used Singly And Dually With/Without Refuge In The Asian Corn Borer

Insect resistant transgenic crops have led to a revolutionary success of pest control.However,the success of this technology has been diminished by the evolution of resistance in target pests.The adaptation of proper insect resistance management program could favor the sustainable use of this approach.High-dose refuge and pyramid strategies that have been broadly adopted are considered to delay the evolution of resistance in target insects based on theoretical models in certain conditions.However,there is limited evidence from empirical experiments to test their realistic function levels,especially in various conditions.In 2020,two domestic Bt maize events targeting the Asian corn borer(ACB)Ostrinia furnacalis have been certified for safety planting.We need to adopt a suitable IRM strategy when those Bt maize are practically plating.In this study,we evaluate the evolution of resistance in the ACB to Bt toxins when they were exposed to single or dual toxins with/without refuge.The experiments were conducted in the laboratory with diet mixed selection method.Cry1 Ab,Cry1F,and Cry1 Ie were used in single or dual,which would result in over 90% selection pressure.Treatments also include three levels of refuge [ration(S/R)of refuge(susceptible,S)vs survival(resistant,R)from each generation of selection are 3:7,5:5 and 7:3).The results indicated that the evolution of resistance to three Bt toxins were different in the ACB.The LC50 s did not significantly change until 5 generations of selection with Cry1 Ab.The resistance ratio(RR)was 16,21 and 27 after 5,6 and 13 generations of selection.In contrast,the RR was 400,and 508 after 3 generation of selection with Cry1 Ie,and Cry1 F,and 780(highest concentration tested killed less than 50%)and 542 after 4 generations of selection.The RR was 890 after 13 generations of selection with Cry1 F.Dual toxins were relatively slow down the resistance development.The RR for Cry1 Ab was 1.7,and 8.6 after 12 and 11 generations of selection with Cry1Ab+Cry1F and Cry1Ab+Cry1Ie,respectively.The RR for Cry1 F or Cry1 Ie were 370 and 304 after 12 and 11 generations of selection with Cry1Ab+Cry1F and Cry1Ab+Cry1Ie,respectively.After 11 generation of selection,together with S/R of 3:7,5:5 and 7:3,the RR for Cry1 Ab was 6.2,1.8 ? 1.7 for the strain selected with Cry1 Ab alone,1.7,1.3 and 1.2 for the strain selected with Cry1Ab+Cry1F,and 1.3,1.1 and 2.2 for the strain selected with Cry1Ab+Cry1Ie.By the conservative criterion of no overlap between the 95% CIs,The RR for Cry1 Ab after 11 generation of selection,together with S/R of 5:5 and 7:3 did not differ significantly among the strain selected with Cry1 Ab or Cry1Ab+Cry1F or Cry1Ab+Cry1Ie.For Cry1 F and Cry1 Ie,the RRs after 11 generations of selection together with S/R of 3:7,5:5 and 7:3 were 58,28 and 11,and 5.1,4.2 and 3.9,respectively.