Resistance Evolution And Resistance Mechanisms In Helicoverpa Armigera (Hübner) Selected With Pyrethroid Plus Organophosphate Mixture

Insecticide mixtures are usually used to enhance the spectrum and efficacy of insect pest control as well as to delay resistance development. Using mixtures as a countermeasure for resistance management in insect pests has been proposed and advocated by several researchers. By theoretical modelling under several hypotheses, it is considered that insecticide mixtures with different mechanisms may delay resistance development. In practice, the hypotheses of the theoretical models can hardly be met in field conditions. Currently, whether the insecticide mixtures could delay resistance development and result in multiple resistance is controversial. In the present study, resistance evolution and resistance mechanisms in Helicoverpa armigera selected with pyrethroid plus organaphosphate mixtures were studied.1. Resistance evolution, cross-resistance in Helicoverpa armigera selected with pyrethroid+organophosphate mixturesThe resistant YS-FP strain and YS-FM strain of Helicoverpa armigera were selected from the susceptible YS strain with a fenvalerate/phoxim mixture (a.i., 1:10) and a fenvalerate/monocrotophos mixture (a.i., 1:50), respectively, for 16 generations. Compared with the YS strain, the YS-FP strain developed 14.7-fold resistance to the fenvalerate/phoxim mixture, 2170-fold resistance to fenvalerate and 3.1-fold resistance to phoxim. The YS-FM strain developed 12.1-fold resistance to the fenvalerate/monocrotophos mixture, 354-fold resistance to fenvalerate and 8.6-fold resistance to monocrotophos. Although YS-FP strain and YS-FM strain developed moderate resistance to mixture itself and the OP component, they had obtained very high level of resistance to fenvalerate.During 16 generations of continuous selection with the fenvalerate/phoxim mixture, the...