Resistance in Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) to new chemistry insecticides.

The control of rice leaffolder, Cnaphalocrocis medinalis (Guenée), depended mainly on the insecticide application in China for a long time, and the resistance development impacted the effects of insecticide application. In this study, 13 conventional and new chemistry insecticides were assayed for the toxicities to the larvae of rice leaffolder collected from Nanning, Changsha, and Nanjing, China, with rice seedling dip method during 2011-2013. Among the tested chemicals, macrolide insecticides spinetoram, spinosad, abamectin, and emanectin benzoate have the highest toxicities, whereas monosultap and Bt have the least toxicities to this insect. Comparing with the baseline data established in 2010, the susceptibilities of rice leaffolder to chlorantraniliprole, metaflumizone, and tebufenozide are declining simultaneously and gradually in the three regions from 2011 to 2013, and C. medinalis are becoming resistance to chlorantraniliprole, metaflumizone, and tebufenozide. The synchronous decreases of susceptibility in three geographic populations were not observed for macrolide insecticides, indoxacarb, chlorpyrifos, monosultap, and Bt. The synchronous insecticide susceptibility declines in field populations of the migratory insect collected from different areas indicated resistance evolution, and the sequence application patterns of different insecticides should be scheduled to delay the further development of resistance along the migratory pathway of the rice leaffolder in China.