Resistance to commonly used insecticides in Asian citrus psyllid: Stability and relationship to gene expression

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), adults were collected from eight citrus groves across central Florida, and the level of insecticide resistance to ten insecticides was measured using a bottle bioassay. The gene expression of five cytochrome P450 CYP4 (CYP4C67, CYP4DA1, CYP4DB1, CYP4G70 and CYP4C68) and three glutathione S‐transferase (GSTD1, GSTE2 and GSTE1) genes was characterized in seven field populations of D. citri and compared with a laboratory population. Additionally, we reared four neonicotinoid insecticide resistant field populations in the laboratory and observed susceptibility changes without exposure to insecticides over multiple generations. The eight field populations of D. citri adults showed no and very low levels of resistance (RR = 1 and 2–10) to dimethoate, chlorprifos, carbaryl, fenpropathrin, bifenthrin, flupyradifurone and spinetoram. Very low to low resistance was found to imidacloprid and cyantraniliprole (RR = 2–10 and RR = 10–20). Moderate to high resistance was found for thiamethoxam (RR = 20–50 and RR = 50–100). The CYP4G70 and CYP4C68 genes were expressed at a higher level in field populations as compared with the laboratory population. Also the Davenport, Florida field population exhibited higher expression of all target genes compared to the laboratory population. Susceptibility to imidacloprid and thiamethoxam increased by 6.62‐ and 6.42‐fold, respectively, compared to the levels initially observed in the field over six generations of breeding without exposure. These results indicate that insecticide resistance may reverse in the field if insecticide selection pressure is removed from the spray schedule or with use of a rotational scheme with insecticides of different modes of action. Also, the results support use of insecticide resistance survey program combined with effective rotation for integrated insecticide resistance management of D. citri where huanglongbing (HLB) management includes vector suppression with insecticides.