The Asian citrus psyllid, Diaphorina citri Kuwayma, is one of the most important pests in citrus production. The objective of this study was to evaluate D. citri resistance management with three insecticide rotations and compare them with no rotation and an untreated check. The different insecticides (modes of action) tested were: dimethoate, imidacloprid, diflubenzuron, abamectin 3% + thiamethoxam 13.9%, and fenpropathrin. Eggs, nymph, and adult psyllids were counted weekly. Five insecticide applications were made in 2016. Insecticide susceptibility was determined by direct comparison with a laboratory susceptible population and field populations before and after all treatments were applied. Rankings of eggs, nymphs, and adults counted in treated plots were significantly lower than in the untreated control plots after each application. Initially, the resistance ratio (RR₅₀) for each rotation model, as compared with laboratory susceptible strain and the field population before application, was less than 5.76 and 4.31, respectively. However, after five applications with dimethoate, the RR₅₀ using the laboratory and pre-treatment field populations was 42.34 and 34.74, respectively. Our results indicate that effectively rotating modes of action can delay and/or prevent development of insecticide resistance in populations of D. citri.

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.

A relatively new insecticide chemistry for controlling sucking insects, afidopyropen, was investigated for toxicity against Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We evaluated the mortality of D. citri eggs, nymphs, and adults treated with afidopyropen using both laboratory-reared and field populations. We also quantified the effects of sublethal doses of afidopyropen on D. citri feeding, host choice selection, and fecundity. For laboratory susceptible adults, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 2.13, 2.00, and 3.08 ng/µL, respectively. For adults collected from a commercially managed citrus grove in Florida, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 1.37, 1.92, and 4.89 ng/µL, respectively. Egg hatch was significantly reduced following exposure to afidopyropen at 100 ng/µL. Furthermore, afidopyropen reduced D. citri nymph survival and adult emergence at concentrations ranging between 0.01 and 100 ng/µL. Diaphorina citri adult feeding decreased on citrus leaves treated with afidopyropen in a concentration-dependent manner as measured indirectly by honeydew excretion, and appeared almost completely inhibited after treatment with 10 and 100 ng/µL solutions of afidopyropen. In choice tests, significantly fewer D. citri adults settled on afidopyropen-treated plants than on control plants at 24, 48, and 72 h after release, with no differences in settling between males and females. Afidopyropen reduced the fecundity of D. citri in a concentration-dependent manner. Collectively, the results suggest that afidopyropen could contribute to the integrated management of D. citri and may therefore be useful in rotational programs to improve resistance management.

Insecticide resistance is an increasing problem in citrus production. The Asian citrus psyllid,Diaphornia citriKuwayama, is recognized as one of the most important citrus pests worldwide and it has developed resistance in areas where insecticides have been overused. The development of insecticide resistance is often associated with fitness costs that only become apparent in the absence of selection pressure. Here, the fitness costs associated with resistance to thiamethoxam and imidacloprid were investigated in three agricultural populations ofD. citrias compared with susceptible laboratory colonies. Results showed that all field populations had greater resistance than laboratory susceptible colonies. For both thiamethoxam and imidacloprid, aCandidatusLiberibacter asiaticus-positive (CLas⁺) colony was more susceptible than theCLas⁻colony. Resistance ratios ranged from 7.65–16.11 for imidacloprid and 26.79–49.09 for thiamethoxam in field populations as compared with a susceptible,CLas⁻laboratory strain. Among three resistant field populations, a significantly reduced net reproductive rate and finite rate of population increase were observed in a population from Lake Wales, FL as compared to both susceptible strains. The fecundity of field populations from Lake Wales, FL was statistically lower than both laboratory susceptible populations. Certain changes in morphological characteristics were observed among resistant, as compared, with susceptible strains. Our data suggest fitness disadvantages associated with insecticide resistance inD. citriare related to both development and reproduction. The lower fitness ofD. citripopulations that exhibit resistance to neonicotinoid insecticides should promote recovery of sensitivity when those populations are no longer exposed to thiamethoxam and/or imidacloprid in the field. The results are congruent with a strategy of insecticide rotation for resistance management.