The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the bacterial pathogen, Candidatus Liberibacter asiaticus, which is the causal agent of huanglongbing (HLB) in the United States. Both short-range and long-range dispersal of D. citri adults affect the spread of HLB; however, little is known about the long-range dispersal capabilities of D. citri in the field or the seasonality of flight behavior. In the present study, an in situ protein marking technique was used to determine the dispersal of D. citri by trapping marked adults under natural field conditions. D. citri movement from abandoned citrus groves to adjacent managed citrus groves was greatest during the spring and summer months and decreased significantly during the colder months (September-March). D. citri were able to traverse potential geographic barriers such as roads and fallow fields. In an experiment conducted to determine long-range dispersal capacity in the absence of severe weather events, D. citri were able to disperse at least 2 km within 12 d. Wind direction was not correlated with the number of marked psyllids captured, indicating substantial flight capability by D. citri. Finally, the number of marked psyllids captured increased with the density of emerging young leaves on surrounding trees. The results confirm that abandoned citrus groves in Florida serve as reservoirs for D. citri, which can disperse across long distances despite geographical barriers.

The spread of vector-transmitted pathogens relies on complex interactions between host, vector and pathogen. In sessile plant pathosystems, the spread of a pathogen highly depends on the movement and mobility of the vector. However, questions remain as to whether and how pathogen-induced vector manipulations may affect the spread of a plant pathogen. Here we report for the first time that infection with a bacterial plant pathogen increases the probability of vector dispersal, and that such movement of vectors is likely manipulated by a bacterial plant pathogen. We investigated how Candidatus Liberibacter asiaticus (CLas) affects dispersal behavior, flight capacity, and the sexual attraction of its vector, the Asian citrus psyllid (Diaphorina citri Kuwayama). CLas is the putative causal agent of huanglongbing (HLB), which is a disease that threatens the viability of commercial citrus production worldwide. When D. citri developed on CLas-infected plants, short distance dispersal of male D. citri was greater compared to counterparts reared on uninfected plants. Flight by CLas-infected D. citri was initiated earlier and long flight events were more common than by uninfected psyllids, as measured by a flight mill apparatus. Additionally, CLas titers were higher among psyllids that performed long flights than psyllid that performed short flights. Finally, attractiveness of female D. citri that developed on infected plants to male conspecifics increased proportionally with increasing CLas bacterial titers measured within female psyllids. Our study indicates that the phytopathogen, CLas, may manipulate movement and mate selection behavior of their vectors, which is a possible evolved mechanism to promote their own spread. These results have global implications for both current HLB models of disease spread and control strategies.

We examined the propensity for flight initiation and flight capability of the Asian citrus psyllid (Diaphorina citri Kuwayama, Hemiptera: Liviidae) with a flight mill. We measured continuous flight by D. citri for up to 3 h, which equated to a distance of as2.4 km. We compared the flight capability of D. citri depending on their sex and morphotype (color of abdomen). Two general morph otypes exist within this species: green-blue and gray-brown. We observed that ' =*32% of psyllids from the green-blue morphotype tested exhibited long durations of flight (>60 s); whereas <5% of psyllids from the gray-brown morphotype performed such long duration flights. There was no significant difference in flight performance between the two sexes within both the gray-brown and green-blue morphotypes. Furthermore, psyllids from the gray-brown morphotype were characterized by smaller pronotums and shorter wings than psyllids from the green-blue morphotype. In addition, males, in general, were characterized by smaller pronotums and shorter wings than females. However, neither pronotum nor wing size were associated with flight capability of D. citri. Our results may help explain dispersal behavior of D. citri with respect to practical management on an area-wide scale.

We investigated how chemical cues derived from female Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) and their host plants affect host acceptance choices by conspecifics. In four-choice cage and two-choice olfactometer assays, female psyllids avoided conspecific female cues in a density-dependent manner. However, odors from citrus plants actively damaged by psyllid feeding were attractive to conspecific females. When odors from feeding-damaged plants were presented simultaneously with odors from female D. citri, attraction of female conspecifics was no longer observed as compared with a clean air control in olfactometer assays. In subsequent experiments, D. citri females were released within arenas that contained actively feeding-damaged or non-damaged (control) citrus plants, each with previously psyllid-infested and uninfested young leaves. D. citri development is linked to the presence of these newly emerging leaves which is the only site of nymphal development. Female D. citri were initially attracted by the actively damaged plants as compared with non-damaged controls. After acceptance of plants that were actively damaged by feeding, D. citri females preferentially chose and settled on uninfested young leaves as compared with previously infested young leaves. A herbivore-induced plant volatile attractant and a femalespecific odor repellent appear to be complementary foraging cues providing psyllids with information at two spatial scales: (1) the whole plant level for choosing a plant potentially harboring male conspecifics for mating, and (2) the within plant level to reduce intra-conspecific competition by identifying previously exploited resources.

1 Redbay ambrosia beetle Xyleborus glabratus is an invasive wood boring beetle that has become established in the southeastern U.S.A. and transmits a fungus Raffaelea lauricola that causes lethal laurel wilt. Among susceptible Lauraceae hosts are redbay Persea borbonia and avocado Persea americana. 2 There is a crucial need for detection of this pest as it moves into new areas.Consequently, our goal was to create a better lure for the monitoring and control of redbay ambrosia beetle. 3 We analyzed volatile emissions of R. lauricola, created a synthetic odour blend based on this analysis and tested this odour blend as a potential attractant in a redbay forest infested with X. glabratus. The synthetic Raffaelea odour blend was not attractive to the beetles by itself. However, it synergistically increased attraction to host-mimic volatiles. 4 We tested four commercial release devices for dispensing Raffaelea odour at various release rates. Two prototypes with the highest release rate, when paired with commercial manuka oil lures, captured more beetles than manuka oil lures alone.These results indicate that a synthetic blend of volatiles based on the odour of the symbiotic fungus of X. glabratus may be useful for the development of more sensitive monitoring lures for this invasive pathogen vector.

Citrus production worldwide is currently threatened by Huanglongbing, or citrus greening disease. The associated pathogen, Candidatus Liberibacter asiaticus (CLas), is transmitted by the Asian citrus psyllid, Diaphorina citri. Annotation of the D. citri genome revealed a reduced innate immune system lacking a number of antimicrobial peptides and the Imd pathway associated with defense against Gram-negative bacteria. We characterized this apparent immune reduction in survival assays in which D. citri were exposed to Gram-negative or Gram-positive bacteria. D. citri experienced significant mortality when exposed to Serratia marcescens (Gram-negative) through oral ingestion or by septic injury. Escherichia coli (Gram-negative) also caused significant D. citri mortality, but only when inoculated at high concentrations through oral ingestion or by septic injury. Neither Micrococcus luteus (Gram-positive) or Bacillus subtilis (Gram-positive) caused significant mortality as compared to controls in any experiment. E. coli titers increased rapidly following exposure, while M. luteus titer remained stable for 72 h. We demonstrate that D. citri is capable of defending against E. coli, a Gram-negative bacterium, despite lacking the Imd defense pathway. The tolerance of D. citri to M. luteus infection, yet inability to effectively clear infections, presents questions to efficacy of D. citri immune response to effectively clear Gram-positive infections.

With an experimental and theoretical modeling approach, it was demonstrated how the combination of behavioral avoidance and low spray coverage can markedly reduce pesticide performance.

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