Insecticide Resistance Monitoring in Field Populations of the Whitebacked Planthopper Sogatella furcifera (Horvath) in China, 2019–2020

Monitoring is an important component of insecticide resistance management. In this study, resistance monitoring was conducted on 18 field populations in China. The results showed that S. furcifera developed high levels of resistance to chlorpyrifos and buprofezin, and S. furcifera showed low to moderate levels of resistance to imidacloprid, thiamethoxam, dinotefuran, clothianidin, sulfoxaflor, isoprocarb and ethofenprox. Sogatella furcifera remained susceptible or low levels of resistance to nitenpyram. LC50 values of nitenpyram and dinotefuran, imidacloprid, thiamethoxam, clothianidin and chlorpyrifos exhibited significant correlations, as did those between dinotefuran and thiamethoxam, clothianidin, sulfoxaflor, imidacloprid, isoprocarb and buprofezin. Similarly, significant correlations were observed between thiamethoxam and clothianidin, sulfoxaflor and imidacloprid. In addition, the activity of EST in field populations of S. furcifera were significantly correlated with the LC50 values of nitenpyram, thiamethoxam and clothianidin. These results will help inform effective insecticide resistance management strategies to delay the development of insecticide resistance in S. furcifera.

Review and Meta-Analysis of the Evidence for Choosing between Specific Pyrethroids for Programmatic Purposes

Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in wild populations. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of susceptibility within the pyrethroid class, and if so, if countries should consider selecting one specific pyrethroid for programmatic use over another. A review of evidence from molecular studies, resistance testing with laboratory colonies and wild populations, and mosquito behavioural assays were conducted to answer these questions. Evidence suggested that in areas where pyrethroid resistance exists, different results in insecticide susceptibility assays with specific pyrethroids currently in common use (deltamethrin, permethrin, α-cypermethrin, and λ-cyhalothrin) are not necessarily indicative of an operationally relevant difference in potential performance. Consequently, it is not advisable to use rotation between these pyrethroids as an insecticide-resistance management strategy. Less commonly used pyrethroids (bifenthrin and etofenprox) may have sufficiently different modes of action, though further work is needed to examine how this may apply to insecticide resistance management.

Review and Meta-Analysis of the Evidence for Choosing Between Specific Pyrethroids for Programmatic Purposes.

Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in wild populations. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of susceptibility within the pyrethroid class, and if so, if countries should consider selecting one specific pyrethroid for programmatic use over another. A review of evidence from molecular studies, resistance testing with laboratory colonies and wild populations, and mosquito behavioural assays was conducted to answer these questions. Evidence suggests that in areas where pyrethroid resistance exists, different results in insecticide susceptibility assays with specific pyrethroids currently in common use (deltamethrin, permethrin, α-cypermethrin and λ-cyhalothrin) are not necessarily indicative of an operationally relevant difference in potential performance. Consequently, it is not advisable to use rotation between these pyrethroids as an insecticide resistance management strategy. Less commonly used pyrethroids (bifenthrin and etofenprox) may have sufficiently different modes of action, though further work would be needed to examine how this may apply to insecticide resistance management.

CHANGES IN SUSCEPTIBILITIES TO INSECTICIDES IN MUSCA DOMESTICA UNDER SELECTION WITH FIPRONIL

New knowledge about resistance and cross-resistance to insecticides of different chemical classes in insects is crucial for correct and effective pest management. This paper reports changes in the susceptibility to insecticides of different chemical classes in the first generations of houseflies Musca domestica L. when they were selected with fipronil. The selection of M. domestica was carried out by feeding adult insects with sugar containing fipronil in a dose that causes the 40–60% mortality of insects. The susceptibility of adults and larvae to insecticides was evaluated by the resistance ratio (RR). In the fipronil-selected strain of M. domestica, the susceptibility to fipronil was unchanged in adults in 3–5 generations and increased in larvae in the fifth generation (RR = 0.5). The susceptibility to deltamethrin decreased in adults of the fourth generation and in larvae of the fifth generation, and the RR was 4.5 and 4.3, respectively, that may suggest the development of cross-resistance in the future. The susceptibility to chlorfenapyr was reduced in adults of fipronil-selected flies of the fourth generation (RR = 1.9). The susceptibility to ivermectin increased in adults of fipronil-selected flies (RR = 0.67) and in larvae of the fifth generation (RR = 0.5). The susceptibility to acetamiprid in the fipronil-selected strain and the laboratory (unselected) strain of M. domestica did not differ. The results are useful for the development of insecticide resistance management programs.