Abstract
The Asian citrus psyllid, Diaphorina citri Kuwayama, is one of the most damaging pests of citrus-producing regions throughout the world. The use of insecticides is the main strategy for controlling psyllid and has increased year by year. In this study, four field populations of D. citri were evaluated for resistance to nine different insecticides using the leaf-dip method. The results showed that the highest level of resistance for D. citri was found in imidacloprid with a resistance ratio of 15.12 in the Zengcheng population compared with the laboratory susceptible population. This was followed by chlorpyriphos (6.47), dinotefuran (6.16), thiamethoxam (6.04), lambda-cyhalothrin (4.78), and bifenthrin (4.16). Piperonyl butoxide (PBO) and triphenyl phosphate (TPP) showed significant synergism on imidacloprid effects in the Zengcheng population (3.84- and 2.46-fold, respectively). Nevertheless, diethyl maleate (DEM) had no synergism on imidacloprid. Biochemical enzyme assays suggested that general esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities were higher in the field-collected populations than in the laboratory susceptible population. However, glutathione S-transferase may play a minor role in the resistance of adult D. citri to insecticides. At the molecular level, resistance of D. citri to imidacloprid is mainly related to the increased expression of CYP4C68 and CYP4G70 (>5-fold).
Highlights
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, was first described in Taiwan in 1907, and ACP can be found in most tropical and subtropical citrus-growing regions[1,2]
No data were available for the susceptibility of the ACP population to insecticides in China
The ACP had developed different levels of resistance to several insecticides among field populations when compared with the susceptible population
Summary
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, was first described in Taiwan in 1907, and ACP can be found in most tropical and subtropical citrus-growing regions[1,2]. Insecticides with different modes of action (organophosphate, neonicotinoids, pyrethroids or carbamate) are often used to control the ACP. In some instances, growers repeated sequential use of the same insecticide or insecticides with the same mode of action Under such selection pressure, the resistance of ACP to organophosphate, pyrethroid, neonicotinoid and carbamate insecticides has been observed. There is an urgent need to evaluate the severity of insecticide resistance to ACP populations in China and develop a resistance management strategy that maintains the effective use of all classes of insecticides for ACP control. Treatment with dsRNA caused reduced the expression of the five CYP4 genes and the mortality of ACP exposed to imidacloprid increased[25] These results demonstrated that the five CYP4 genes were associated with imidacloprid resistance in ACP. It was unclear which of the five CYP4 genes played an important role in imidacloprid resistance
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