The Asian citrus psyllid (Diaphorina citri Kuwayama) is an insect pest capable of transmitting Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening in North America. D. citri also harbors three endosymbionts, Wolbachia, Candidatus Carsonella ruddii, and Candidatus Profftella armatura, which may influence D. citri physiology and fitness. Although genomic researches on these bacteria have been conducted, much remains unclear regarding their ecology and inter-population variability in D. citri. The present work examined the densities of each endosymbiont in adult D. citri sampled from different populations using quantitative PCR. Under field conditions, the densities of all three endosymbionts positively correlated with each other, and they are associated with D. citri gender and locality. In addition, the infection density of CLas also varied across populations. Although an analysis pooling D. citri from different populations showed that CLas-infected individuals tended to have lower endosymbiont densities compared to uninfected individuals, the difference was not significant when the population was included as a factor in the analysis, suggesting that other population-specific factors may have stronger effects on endosymbiont densities. To determine whether there is a genetic basis to the density differences, endosymbiont densities between aged CLas-negative females of two D. citri populations reared under standardized laboratory conditions were compared. Results suggested that inter-population variability in Wolbachia infection density is associated with the genotypes of the endosymbiont or the host. Findings from this work could facilitate understanding of D. citri-bacterial associations that may benefit the development of approaches for managing citrus greening, such as prevention of CLas transmission.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-016-0733-9) contains supplementary material, which is available to authorized users.

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.

Several maize, Zea mays L., inbred lines developed from an Antiguan maize population have been shown to exhibit resistance to numerous aboveground lepidopteran pests. This study shows that these genotypes are able to significantly reduce the survival of two root feeding pests, western corn rootworm, Diabrotica virgifera virgifera LeConte, and southern corn rootworm, Diabrotica undecimpunctata howardi Barber. The results also demonstrated that feeding by the aboveground herbivore fall armyworm, Spodoptera frugiperda (J. E. Smith), before infestation by western corn rootworm reduced survivorship of western corn rootworm in the root tissues of some, but not all, genotypes. Likewise, the presence of western corn rootworm in the soil seemed to increase resistance to fall armyworm in the whorl in several genotypes. However, genotypes derived from the Antiguan germplasm with genetic resistance to lepidopterans were still more resistant to the fall armyworm and both rootworm species than the susceptible genotypes even after defense induction. These results suggest that there may be intraplant communication that alters plant responses to aboveground and belowground herbivores.