Phytoene desaturase-silenced citrus as a trap crop with multiple cues to attract Diaphorina citri, the vector of Huanglongbing.

Huanglongbing (HLB) is one of the most destructive diseases in citrus worldwide. Unfortunately, HLB has no cure and management relies on insecticides to reduce populations of the vector, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We propose an attract-and-kill strategy using a trap crop as an alternative to vector control to reduce transmission of the pathogen, 'Candidatus Liberibacter asiaticus'. We evaluated vector response to phytoene desaturase-silenced citrus trees using virus-induced gene silencing technology. Citrus tristeza virus (CTV) was used to produce a phytoene desaturase-silenced citrus (CTV-tPDS) that expresses visual, olfactory, and gustatory cues to attract D. citri. We found that D. citri were more attracted to CTV-tPDS plants with noticeably better fecundity and overall population fitness than on control plants. Moreover, rearing D. citri on CTV-tPDS plants significantly increased their survival probability compared with those reared on control plants. CTV-tPDS plants possessed reduced content of both carotenoid and chlorophyll pigments resulting in a consistent photobleached phenotype on citrus leaves which provided a sufficient close-range visual attractant to stimulate D. citri landing. Additionally, CTV-tPDS plants exhibited an enriched profile of volatile organic compounds (VOCs), which offered adequate olfactory cues to attract psyllid from long-range. Finally, CTV-tPDS plants exhibited an enriched metabolite content of phloem sap and leaves which offered appropriate gustatory cues that influenced probing/feeding behavior. We believe that introducing CTV-tPDS plants (as a trap crop) to D. citri-infested orchards will attract and congregate psyllids to facilitate their removal from the target crop with insecticides or by other means. This new strategy could be deployed relatively quickly and economically to HLB-impacted citrus industries. Moreover, it is an eco-friendly strategy because it should partially reduce the input of chemical insecticides ameliorating the indirect cost of HLB infection.

A Multimodal Attract-and-Kill Device for the Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae).

Phytophagous insects, including Asian citrus psyllids (Diaphorina citri Kuwayama), use multiple sensory modalities (vision, olfaction, and gustation,) to locate and accept host plants. We explored incorporation of several sensory cues into a multi-modal attract-and-kill device (AK device) using a three-dimensional shape to increase visibility, as well as elements of color, attractant, phagostimulant, UV reflectant, and toxicant. Attraction of adult D. citri to the device was mediated by a combination of a highly reflective yellow cylinder, a UV reflectant compound (magnesium oxide), and an odorant blend as a short-range attractant. The device surface was coated with a slow-release wax matrix (SPLAT™) augmented with a phagostimulant consisting of a 3-component blend (formic acid, acetic acid, and para-cymene) and an insecticide (ß-cyfluthrin). Psyllids landing on the device attempted to feed from the wax matrix, became intoxicated, died, and fell from the device. The device remained fully active over a period of 12 weeks partly because dead psyllids or nontargets did not adhere to the surface as occurs on adhesive yellow sticky cards, the industry standard. Laboratory and field assays showed that the device attracted and killed significantly more adult D. citri than ordinary yellow sticky cards. This device or a future iteration based on the design elements of this device is expected to contribute to sustainable and environmentally appropriate management of D. citri by exploiting the psyllid's innate behavioral responses to visual, olfactory, and gustatory stimuli.

Attributes of Yellow Traps Affecting Attraction of Diaphorina citri (Hemiptera: Liviidae).

Laboratory assays were conducted to evaluate responses of Diaphorina citri to various aspects of visual cues associated with traps in an effort to improve trap effectiveness. Addition of white or UV violet but not yellow light-emitting diodes (LEDs) increased attraction to standard yellow adhesive traps moderately (11-17%), with no difference in attraction between white or UV violet LEDs. Addition of a black border on yellow traps enhanced collections. However, there were no differences between attraction to black patterns on traps. Comparisons were made between different commercial paints, some with UV-reflecting properties or fluorescence. A yellow paint with UV reflectance, used for painting bird decoys (decoy yellow), was more attractive than the standard yellow Olson sticky trap. Addition of white or green pigment to increase intensity or enhance green reflectance, respectively, did not increase attraction. Alteration of reflectance of Olson traps with addition of UV-reflecting or fluorescent pigments did not enhance attraction of D. citri. In field comparisons, decoy yellow and fluorescent yellow sticky traps were more attractive to D. citri than Olson yellow.

UV reflective properties of magnesium oxide increase attraction and probing behavior of Asian citrus psyllids (Hemiptera: Liviidae).

Asian citrus psyllid (Diaphorina citri) vectors the bacterium Candidatus Liberibacter asiaticus, the causal pathogen of citrus greening disease that is devastating citrus industries worldwide. Suppressing psyllid populations is crucial to prevent disease spread. An attract-and-kill trap based on psyllid behavior would fill a niche for monitoring and control. To optimize visual attraction of psyllids, the ultraviolet (UV) reflective properties of magnesium oxide (MgO) and/or barium sulfate (BaSO4) were assessed for potential application to a trap surface. Under low UV, high UV and natural sunlight conditions, the reflectance, attraction, and probing behaviors of psyllids were evaluated on surfaces containing magnesium oxide or barium sulfate. Magnesium oxide added to yellow sticky traps enhanced visual response of D. citri. Probing assays demonstrated that magnesium oxide alone or as a mixture with a phagostimulant blend, increased the UV reflectance of substrates, as well as, attraction and probing by psyllids. Results demonstrated that psyllids respond to both short (UV) and long (yellow) wavelengths during orientation, and that these inert compounds can increase UV reflectance and improve attractiveness of an attract-and-kill device.

Author Correction: Multidimensional approach to formulating a specialized diet for northern corn rootworm larvae.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Development of an improved and accessible diet for western corn rootworm larvae using response surface modeling.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is an important pest of maize (Zea mays L.). Published WCR diets contain corn root powder, which is not available for purchase, thereby limiting the practical use of diets containing this ingredient. We applied response surface modeling combined with mixture designs to formulate a WCR diet that does not require corn root powder. We developed the new formulation by systematically exploring eight protein ingredients from animal, plant, and yeast sources based on simultaneous evaluation of three life history parameters (weight, molting, and survival). This formulation (WCRMO-2) without corn root powder supported approximately 97% of larval survival and successful molting. Larval weight gain after 10 days of feeding on WCRMO-2 was 4-fold greater than that of larvae feeding on the current best published WCR diet. Additionally, there was no significant difference in these larval performance traits when larvae were reared on WCRMO-2 and the best proprietary WCR diet. A commercial version of WCRMO-2 was tested and found to perform comparably for these traits. These improvements met our goal of a diet comprised of available ingredients that supports performance of WCR larvae equal to or better than publicly available formulations and proprietary formulations.

Hexaacetyl-chitohexaose, a chitin-derived oligosaccharide, transiently activates citrus defenses and alters the feeding behavior of Asian citrus psyllid.

Plants have a perception system triggered by pathogen and pest signals to initiate defense. These signals include evolutionarily conserved molecules from microbes and insects termed pathogen/herbivore-associated molecular patterns (PAMPs/HAMPs). Here we showed that hexaacetyl-chitohexaose (HC), an oligosaccharide from chitin, a structural component in insect exoskeletons and fungi cell walls, upregulated defense-associated genes WRKY22, GST1, RAR1, EDS1, PAL1 and NPR2, and downregulated ICS1 at 1 h after HC treatment in Sun Chu Sha mandarin leaves. The effect was transient as defense gene transcriptional changes were not observed at 18 h after the treatment. Electrical penetration graph (EPG) recordings were used to study the feeding behavior of Asian citrus psyllid (ACP) following the HC treatment. ACP is the hemipteran vector of Candidatus Liberibacter asiaticus (CLas), the pathogen associated with huanglongbing (HLB). Adult ACP displayed reduced intercellular probing, reduced xylem feeding count and duration, and increased non-probing activity on HC-treated citrus compared to controls. During an 18-h recording, percentage for total duration of xylem ingestion, phloem ingestion, intercellular probing were lower, and the percentage of non-probing behavior was higher in HC-treated leaves than in controls. In host-selection behavior studies, HC treatment did not alter the attractiveness of citrus leaves under light or dark conditions. In addition, ACP feeding on HC-treated leaves did not show differences in mortality for up to 10 day of exposure. In summary, we report that HC induced a transient defense in citrus and an inhibitory effect on ACP feeding but did not affect host selection or the insect fitness under the tested conditions.

Multidimensional approach to formulating a specialized diet for northern corn rootworm larvae.

The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is a major pest of maize (Zea mays L.). This pest has developed resistance to insecticides and adapted to crop rotation and may already be in the early stages of adaptation to toxins produced by Bacillus thuringiensis (Bt). Toxicity bioassays using artificial diet have proven to be valuable for monitoring resistance in many species, but no artificial diet has been developed specifically for NCR larvae. Toward this end, we first evaluated known Diabrotica diets to identify a starting media. We then developed a specialized diet for NCR using an iterative approach. Screening designs including 8 diet components were performed to identify the principal nutritional components contributing to multiple developmental parameters (survival, weight, and molting). We then applied mixture designs coupled with response surface modeling to optimize a blend of those components. Finally, we validated an improved NCR diet formulation that supports approximately 97% survival and molting, and a 150% increase in larval weight after 10 days of feeding compared with the best previously published artificial diet. This formulation appears suitable for use in diet bioassays as a tool for evaluating the resistance of NCR populations to insecticides.

Host-plant resistance associated with Poncirus trifoliata influence oviposition, development and adult emergence of Diaphorina citri (Hemiptera: Liviidae).

BACKGROUND: The Asian citrus psyllid, Diaphorina citri Kuwayama, is the primary vector of the phloem-inhabiting bacterium Candidatus Liberibacter asiaticus putatively responsible for citrus greening (huanglongbing), a devastating citrus disease. Infestations of D. citri frequently develop on Citrus and other genera within the Rutaceae subfamily Aurantioideae including Murraya and Bergera. The genotype Poncirus trifoliata is also a member of the Aurantioideae and readily hybridizes with Citrus spp., but colonization by D. citri is reduced on this genotype. RESULTS: Working with young potted seedlings grown in a greenhouse, we found that the development of D. citri immatures on four P. trifoliata cultivars, especially 'Kryder 55-5', was slower compared with the development of immatures on the susceptible Citrus macrophylla. In choice assays, adult psyllids exhibited antixenotic behavior towards accessions of P. trifoliata and laid fewer eggs on this genotype compared with C. macrophylla. CONCLUSIONS: Based on reduced oviposition and delays in development, P. trifoliata exhibits a combination of antixenosis and antibiosis host-plant resistance to D. citri. A companion plant assay showed that the presence of C. macrophylla stimulated higher oviposition rates on P. trifoliata, but nymph development remained retarded on P. trifoliata. Here, we show that the antixenosis associated with trifoliate accessions can be overcome to some extent by the presence of a preferred susceptible host plant; but in combination with antibiosis P. trifoliata remains an inferior host plant. © 2018 Society of Chemical Industry.

Prolonged phloem ingestion by Diaphorina citri nymphs compared to adults is correlated with increased acquisition of citrus greening pathogen.

Citrus greening disease (huanglongbing), currently the most destructive citrus disease worldwide, is putatively caused by Candidatus Liberibacter asiaticus (CLas), a phloem-limited bacterium transmitted by the Asian citrus psyllid Diaphorina citri. Electrical penetration graph (EPG) recordings over 42 h were performed to compare the feeding behavior of D. citri adults and 4th or 5th instar nymphs feeding on CLas-infected or healthy citron plants. Nymphs performed more individual bouts of phloem ingestion (E2) and recorded longer phloem ingestion total time compared with adults, whereas adults performed more bouts of xylem ingestion (G) and recorded greater total time of xylem ingestion compared with nymphs. Quantitative polymerase chain reaction tests indicated that 58% of nymphs and 6% of adults acquired CLas during the 42 h EPG-recorded feeding on infected plants. In a histological study, a greater proportion of salivary sheaths produced by nymphs were branched compared to those of the adults. Our results strongly suggest that more bouts and longer feeding time in the phloem by nymphs may explain their more efficient CLas acquisition from infected plants compared to adults. This is the first EPG study comparing nymphs and adults of D. citri on healthy and infected citrus plants in relation to CLas acquisition.

Diet improvement for western corn rootworm (Coleoptera: Chrysomelidae) larvae.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is the most serious insect pest of corn (Zea mays L.) in the United States and parts of Europe, and arguably one of the world's most expensive pests to control. Several diet formulations are currently used by industry and public researchers to evaluate WCR larvae in diet-toxicity bioassays. However, a publicly available diet that produces normative insects that are physiologically similar to WCR larvae reared on corn roots will accelerate development of management technologies. We report a new diet formulation that supports improved weight gain, larval development and survival compared with the only public diet for WCR that is currently available in the refereed literature. The formulation was created by using response surface methods combined with n-dimensional mixture designs to identify and improve the formulation of key ingredients. Weight gain increased two-fold, and survival and molting rates increased from 93% and 90%, respectively when reared on the public diet, to approximately 99% for both survival and molting at 11 days when reared on our new formulation. This new formulation provides a standardized growth medium for WCR larvae that will facilitate comparison of research results from various working groups and compliance with regulatory requirements.

Use of Mixture Designs to Investigate Contribution of Minor Sex Pheromone Components to Trap Catch of the Carpenterworm Moth, Chilecomadia valdiviana.

Field experiments were carried out to study responses of male moths of the carpenterworm, Chilecomadia valdiviana (Lepidoptera: Cossidae), a pest of tree and fruit crops in Chile, to five compounds previously identified from the pheromone glands of females. Previously, attraction of males to the major component, (7Z,10Z)-7,10-hexadecadienal, was clearly demonstrated while the role of the minor components was uncertain due to the use of an experimental design that left large portions of the design space unexplored. We used mixture designs to study the potential contributions to trap catch of the four minor pheromone components produced by C. valdiviana. After systematically exploring the design space described by the five pheromone components, we concluded that the major pheromone component alone is responsible for attraction of male moths in this species. The need for appropriate experimental designs to address the problem of assessing responses to mixtures of semiochemicals in chemical ecology is described. We present an analysis of mixture designs and response surface modeling and an explanation of why this approach is superior to commonly used, but statistically inappropriate, designs.

The Fungus Raffaelea lauricola Modifies Behavior of Its Symbiont and Vector, the Redbay Ambrosia Beetle (Xyleborus Glabratus), by Altering Host Plant Volatile Production.

The redbay ambrosia beetle Xyleborus glabratus is the vector of the symbiotic fungus, Raffaelea lauricola that causes laurel wilt, a highly lethal disease to members of the Lauraceae family. Pioneer X. glabratus beetles infect live trees with R. lauricola, and only when tree health starts declining more X. glabratus are attracted to the infected tree. Until now this sequence of events was not well understood. In this study, we investigated the temporal patterns of host volatiles and phytohormone production and vector attraction in relation to laurel wilt symptomology. Following inoculations with R. lauricola, volatile collections and behavioral tests were performed at different time points. Three days after infection (DAI), we found significant repellency of X. glabratus by leaf odors of infected swamp bay Persea palustris as compared with controls. However, at 10 and 20 DAI, X. glabratus were more attracted to leaf odors from infected than non-infected host plants. GC-MS analysis revealed an increase in methyl salicylate (MeSA) 3 DAI, whereas an increase of sesquiterpenes and leaf aldehydes was observed 10 and 20 DAI in leaf volatiles. MeSA was the only behaviorally active repellent of X. glabratus in laboratory bioassays. In contrast, X. glabratus did not prefer infected wood over healthy wood, and there was no associated significant difference in their volatile profiles. Analyses of phytohormone profiles revealed an initial increase in the amount of salicylic acid (SA) in leaf tissues following fungal infection, suggesting that the SA pathway was activated by R. lauricola infection, and this activation caused increased release of MeSA. Overall, our findings provide a better understanding of X. glabratus ecology and underline chemical interactions with its symbiotic fungus. Our work also demonstrates how the laurel wilt pathosystem alters host defenses to impact vector behavior and suggests manipulation of host odor by the fungus that attract more vectors.

Sclerenchymatous ring as a barrier to phloem feeding by Asian citrus psyllid: Evidence from electrical penetration graph and visualization of stylet pathways.

Asian citrus psyllid (Diaphorina citri) feeding behaviors play a significant role in the transmission of the phloem-limited Candidatus Liberibacter asiaticus (CLas) bacterium that causes the economically devastating citrus greening disease. Sustained phloem ingestion by D. citri on CLas infected plants is required for pathogen acquisition and transmission. Recent studies have shown a fibrous ring of thick-walled sclerenchyma around the phloem in mature, fully expanded citrus leaves that is more prominent on the abaxial compared with the adaxial side. The composition and thickness of this fibrous ring may have an important role in selection of feeding sites by D. citri based on leaf age and leaf surface, which in turn can affect pathogen acquisition and transmission. We measured feeding behavior using electrical penetration graph (EPG) recordings of individual D. citri adults placed on abaxial or adaxial surfaces of young or mature Valencia orange leaves to study the role of the sclerenchymatous ring in modifying D. citri feeding behavior. Feeding sites on the same leaf tissues were then sectioned and examined by epifluorescence microscopy. The duration of phloem ingestion (E2 waveform) by psyllids was significantly reduced on mature compared with young leaves, and on abaxial compared with adaxial leaf surfaces. The longest duration of phloem ingestion was observed from psyllids placed on the adaxial side of young leaves that had the least developed sclerenchyma. Bouts of phloem salivation (E1 waveform), however, were significantly longer on mature leaves compared with young leaves. D. citri adults made consecutive phloem feeding attempts (bouts) on the abaxial side of mature leaves and those bouts resulted in unsuccessful or shorter periods of phloem ingestion. Adults also made more frequent and longer bouts of xylem ingestion on mature leaves compared with adult psyllids placed on young leaves. Epifluorescence microscopy showed that the fibrous ring in young leaves was thinner and autofluoresced in red whereas the ring in mature leaves was thicker and autofluoresced in blue, indicating changes in structure and composition (e.g., lignification) of sclerenchyma correlated with leaf age. Our results support the hypothesis that the presence of a thick, well-developed fibrous ring around phloem tissues of mature leaves acts as a barrier to frequent or prolonged phloem ingestion by D. citri from citrus leaves. This may have an important role in limiting or preventing CLas acquisition and/or transmission by D. citri, and could be used for identification and development of resistant citrus cultivars.

Expression of Bacillus thuringiensis cytolytic toxin (Cyt2Ca1) in citrus roots to control Diaprepes abbreviatus larvae.

Diaprepes abbreviatus (L.) is an important pest of citrus in the USA. Currently, no effective management strategies of D. abbreviatus exist in citriculture, and new methods of control are desperately sought. To protect citrus against D. abbreviatus a transgenic citrus rootstock expressing Bacillus thuringiensis Cyt2Ca1, an insect toxin protein, was developed using Agrobacterium-mediated transformation of 'Carrizo' citrange [Citrus sinensis (L) Osbeck Poncirus trifoliate (L) Raf]. The transgenic citrus root stock expressed the cytolytic toxin Cyt2Ca1 constitutively under the control of a 35S promoter in the transgenic Carrizo citrange trifoliate hybrid including the roots that are the food source of larval D. abbreviatus. The engineered citrus was screened by Western blot and RT-qPCR analyses for cyt2Ca1 and positive citrus identified. Citrus trees expressing different levels of cyt2Ca1 transcripts were identified (Groups A-C). High expression of the toxin in the leaves (109 transcripts/ng RNA), however, retarded plant growth. The transgenic plants were grown in pots and the roots exposed to 3week old D. abbreviatus larvae using no-choice plant bioassays. Three cyt2Ca1 transgenic plants were identified that sustained less root damage belonging to Group B and C. One plant caused death to 43% of the larvae that fed on its roots expressed 8×106cyt2Ca1 transcripts/ng RNA. These results show, for the first time, that Cyt2Ca1 expressed in moderate amounts by the roots of citrus does not retard citrus growth and can protect it from larval D. abbreviatus.

Machine Learning for Characterization of Insect Vector Feeding.

Insects that feed by ingesting plant and animal fluids cause devastating damage to humans, livestock, and agriculture worldwide, primarily by transmitting pathogens of plants and animals. The feeding processes required for successful pathogen transmission by sucking insects can be recorded by monitoring voltage changes across an insect-food source feeding circuit. The output from such monitoring has traditionally been examined manually, a slow and onerous process. We taught a computer program to automatically classify previously described insect feeding patterns involved in transmission of the pathogen causing citrus greening disease. We also show how such analysis contributes to discovery of previously unrecognized feeding states and can be used to characterize plant resistance mechanisms. This advance greatly reduces the time and effort required to analyze insect feeding, and should facilitate developing, screening, and testing of novel intervention strategies to disrupt pathogen transmission affecting agriculture, livestock and human health.

A Phagostimulant Blend for the Asian Citrus Psyllid.

Chemical cues that elicit orientation by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), are of interest because it is the primary vector of the causal pathogen of citrus greening disease. Non-pesticidal control methods for D. citri remain a high priority for the citrus industry. While searching for semiochemicals that may be involved in orientation to host plants, we previously identified a blend of formic and acetic acids that stimulated substrate probing by D. citri. Here, we applied geometric mixture designs and response surface modeling to identify and optimize a 3-component blend that further increased the number of salivary sheaths produced by D. citri on a wax substrate containing a 3.5:1.6:1 blend of formic acid, acetic acid, and p-cymene, respectively. No evidence was found for remote orientation by D. citri adults through olfaction to the phagostimulant blends. Increased probing in response to the presence of phagostimulants in the wax matrix occurred after contact with the substrate. Yellow wax beads always attracted more D. citri adults and received more probes compared with white wax beads. Yellow beads containing the 3-component blend of phagostimulants were probed by D. citri 2 to 3 times more often compared with yellow beads alone. The phagostimulant effect also was tested by covering wax beads containing the 3-component blend with a plastic film to minimize olfaction or contact chemoreception by antennation. The plastic film did not affect the probing response, thus suggesting that chemosensation was associated with mouthparts and not olfactory receptors. Salivary sheaths produced in wax beads containing the phagostimulant blend were 4.5 times longer than sheaths produced in beads without tastants. This phenomenon might be used to improve a trap, design an attract-and-kill product, or enhance other means of managing D. citri and citrus greening disease.

Formic and Acetic Acids in Degradation Products of Plant Volatiles Elicit Olfactory and Behavioral Responses from an Insect Vector.

Volatile phytochemicals play a role in orientation by phytophagous insects. We studied antennal and behavioral responses of the Asian citrus psyllid, Diaphorina citri, vector of the citrus greening disease pathogen. Little or no response to citrus leaf volatiles was detected by electroantennography. Glass cartridges prepared with ß-ocimene or citral produced no response initially but became stimulatory after several days. Both compounds degraded completely in air to a number of smaller molecules. Two peaks elicited large antennal responses and were identified as acetic and formic acids. Probing by D. citri of a wax substrate containing odorants was significantly increased by a blend of formic and acetic acids compared with either compound separately or blends containing ß-ocimene and/or citral. Response surface modeling based on a 4-component mixture design and a 2-component mixture-amount design predicted an optimal probing response on wax substrate containing a blend of formic and acetic acids. Our study suggests that formic and acetic acids play a role in host selection by D. citri and perhaps by phytophagous insects in general even when parent compounds from which they are derived are not active. These results have implications for the investigation of arthropod olfaction and may lead to elaboration of attract-and-kill formulations to reduce nontarget effects of chemical control in agriculture.

Investigating dormant-season application of pheromone in citrus to control overwintering and spring populations of Phyllocnistis citrella (Lepidoptera: Gracillariidae).

BACKGROUND: The leafminer, Phyllocnistis citrella Stainton, reproduces on leaf flush during winter. Deployment of pheromone during winter could suppress moth populations in spring and summer more than a spring application alone. We tested the primary pheromone component of P. citrella, (Z,Z,E)-7,11,13-hexadecatrienal, released gradually over several months from elastomeric dispensers in a citrus grove in 6.4 ha main plots in winter and/or 3.2 ha subplots in spring (834 mg triene ha(-1) ) and evaluated moth catch and leaf mining. RESULTS: After winter treatment, dispensers provided >85% disruption of male moth catch in traps for 37 weeks, and after spring treatment they provided >92% disruption for 26 weeks, but there was only a 12% reduction in leaf infestation in spring. Two applications were no better than only a single application in spring. Disruption of moth catch was weaker in treated plots where traps were placed high (3.1 m) rather than low (1.6 m) in the tree canopy. CONCLUSION: Dispensers provided effective and persistent disruption of male catch in pheromone-baited monitoring traps but were minimally effective in reducing leaf infestation by P. citrella. Winter application of pheromone did not reduce leaf mining in spring compared with spring application alone. Tops of trees may have provided a refuge for mating. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Chemical and behavioral analysis of the cuticular hydrocarbons from Asian citrus psyllid, Diaphorina citri.

Huanglongbing (HLB) is the most destructive disease of citrus worldwide. The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the vector of the phloem-inhabiting bacterium, Candidatus Liberibacter asiaticus, which is presumed to cause HLB in Florida citrus. Laboratory and field studies were conducted to examine the behavioral responses of male and female D. citri to their cuticular extracts. In olfactometer assays, more male D. citri were attracted to one, five, or 10 female cuticular extract equivalent units than blank controls. The results were confirmed in field studies in which clear or yellow traps baited with 10 female cuticular extract equivalent units attracted proportionately more males than clear traps baited with male cuticular extract or unbaited traps. Analyses of cuticular constituents of male and female D. citri revealed differences between the sexes in chemical composition of their cuticular extracts. Laboratory bioassays with synthetic chemicals identified from cuticular extracts indicated that dodecanoic acid attracted more males than clean air. Traps baited with dodecanoic acid did not increase total catch of D. citri as compared with blank traps at the dosages tested; however, the sex ratio of psyllid catch was male biased on traps baited with the highest lure loading dosage tested (10.0 mg).