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United States Department of Agriculture

Agricultural Research Service

2011 Annual Report

1a.Objectives (from AD-416)
To characterize plant responses to feeding by horticultural pests, identify sources and genetic mechanisms of plant resistance to subtropical pests, and select resistant germplasm. To develop and implement biological control programs that reduce the economic importance of subtropical pests of horticultural crops. To increase our knowledge of salient aspects of the biology and behavior of invasive horticultural pests in association with their host plants and natural enemies. Identify combinations of pest control tactics for pests of floricultural and nursery/landscape plants that interact synergistically to improve pest control, are practical to implement, and will minimize environmental disruption.

1b.Approach (from AD-416)
IPM strategies based on biological control will be developed. Natural control of subtropical insect pests by native and imported biological control agents will be assessed, and methods of conservation and augmentation to boost natural control by these agents will be investigated. Exotic biological control agents for invasive insect pests will be identified through literature reviews, collaborations with foreign scientists, or foreign exploration; adhering to federal and state regulations, these agents will be imported into the US, evaluated under federal or state quarantine facilities, released and monitored for establishment and impact. IPM strategies based on plant resistance will be developed. Insect bioassays and field trials will be conducted to identify plant varieties that are pest resistant. Citrus, vegetable and ornamental germplasm as well as non-host plant species will be screened; genes associated with insect resistance will be cloned, characterized and considered for cultivar improvement through traditional and transgenic procedures. When plant resistance is found, plant products responsible for resistance will be identified and explored for use in IPM. Transgenic plants produced at USHRL or elsewhere will be evaluated for effects on insect biology, resistance to pests, and disease transmission by insect vectors. The genetic bases of insect biology and of interactions among insect vectors, plant pathogens and host plants will be investigated using molecular techniques and genomics analyses, and IPM opportunities based on these investigations will be pursued. Molecular techniques will be used to examine the biology, gene expression and biochemical pathways of exotic insect pests. Vector-pathogen relations will be characterized biochemically and biologically, and the results will be applied to insect pest problems. Research on insect biology and behavior will be conducted to advance IPM. Biorationals such as entomopathogenic fungi, viruses and bacteria, microbials, sugar esters, oils, and azadiractin that have potential as environmentally benign IPM components will be identified and assessed. Methods of monitoring and estimating infestation densities of insect pests and their natural enemies will be developed including traps baited with attractants and sampling protocols. The ecology of insect pests and their natural enemies will be assessed in relation to pest management.

3.Progress Report
A putative pheromone of Diaprepes root weevil has been identified and is being synthesized. A new plant volatile was discovered that consistently elicits antennal response. Citrus was transformed to express a Bacillus thuringiensis toxin gene active against Coleoptera and is being propagated for experiments to determine if it reduces infestations of Diaprepes root weevil. Methods for managing citrus leafminer using a synthetic sex pheromone continued. We have worked closely with industry to develop two novel control products including Specialized Pheromone and Lure Application Technology-citrus leafminer (SPLAT-CLM) and MalEx. Research in Florida documented that injury by the citrus leafminer to citrus leaves exacerbates the incidence and severity of citrus canker disease. Studies on the Asian citrus psyllid (ACP) feeding mechanism led to the identification of molecules that inhibit the production of psyllid salivary sheaths during the feeding process. We began exploring this as a new area of interdiction that could be used as a psyllid control strategy. Research on flight activity of the ACP revealed that the psyllid routinely disperses to and from citrus trees at distances of up to 500 feet, with flight activity occurring any time during the year and consistent activity distant to citrus occurring every spring.

The citrus genotype Poncirus trifoliata exhibited resistance to infestations of Asian citrus psyllid in choice and no-choice experiments. This is a common citrus species that could be used in a traditional breeding program aimed at developing a commercial cultivar with psyllid resistance to mitigate huanglongbing disease. Tamarixia radiata, a parasite of ACP, was found to be widespread and common in urban plantings of a psyllid host plant, orange jasmine, although levels of control by the parasitoid were relatively low. The presence and relative titers of the huanglongbing bacterium were assessed in the alimentary canal, salivary glands and other organs of its vector, the ACP. The salivary glands appear to constitute a major transmission barrier for the pathogen.

A new bioassay was developed for assessing transmission by ACP of the pathogen responsible for citrus greening disease. This assay is less expensive and faster. A viral pathogen, Diaphorina citri reovirus, was discovered and characterized being shown to infect approximately 50 percent of psyllids in the field. This opens an opportunity to use this already adapted psyllid pathogen as a future management tool to suppress psyllid populations. The entire genome of the ACP was sequenced and made available to the scientific community. Chilli thrips from Japan can be distinguished from chilli thrips populations in the U.S. and most of Asia based on the mitochondrial CO1 gene.

A predatory mite and the insidious flower bug were effective at limiting chilli thrips damage to five different varieties of peppers. The mite was a more efficient predator of thrips nymphs and flower bug was a better predator of adults.

1. First draft genome of the Asian citrus psyllid complete. Agricultural Research Service entomologists at Fort Pierce, FL, established an international genome consortium and completed the first draft genome of the Asian citrus psyllid. The psyllid genome provides a foundation for further investigation of the functional genomics of psyllids, and serves as a reference genome for sequencing of other psyllid species. Genomics enables the elucidation of the genetic basis of key biological processes such as reproduction, pathogen transmission and insecticide resistance; and it provides critical information needed to develop methods for psyllid control and plant improvement to reduce losses to this pest and associated disease affecting the citrus industry.

2. Identification of citrus germplasm with resistance to colonization by Asian citrus psyllid. Citrus greening disease, a serious disease of citrus caused by a bacterium vectored by the Asian citrus psyllid, is threatening citrus production in the United States. The identification and incorporation of traits into citrus that provide resistance to infestations of the psyllid is considered a potential disease management strategy. ARS researchers at Fort Pierce, FL, assessed 87 genotypes of citrus and citrus relatives for their propensity in a free-choice situation for psyllid infestations. Of significance was that, although not completely avoided, very low infestation levels of the psyllid developed on a genotype known as trifoliate orange (Poncirus trifoliata). Trifoliate orange readily forms hybrids with Citrus spp., is commonly incorporated into rootstock varieties, and has been used in breeding advanced scion material. The identification of partial resistance in this germplasm could prove useful in future citrus breeding efforts aimed at reducing the incidence and spread of Huanglongbing.

3. Isolation and characterization of a viral pathogen in the Asian Citrus Psyllid. Few pathogens for psyllid species were known, thus discovery of new biological control agents would bolster efforts to reduce psyllid populations and the spread of the pathogens associated with citrus greening disease. Genomics approaches were used and ARS researchers at Fort Pierce, FL, identified a new psyllid-infecting virus which was similar to the insect-infecting Reovirus group. Comparisons of the virus gene sequences indicated that the virus is in the Family: Reoviridae, Genus: Fijivirus, described from planthoppers which is a closely related insect group. Of significance, while these viruses are wide spread in tropical rice growing regions of the world they had not previously been reported from other insects outside of planthoppers, nor in insects in North America. Insect viral pathogens provide a wealth of molecular opportunities and advance the overall knowledge base of psyllid pathogens, leading to manipulation of the virus-psyllid association, which are being examined for their uses in suppressing psyllid populations and/or reduction of pathogen transmission.

4. Establishment of Asian citrus psyllid cell cultures. Culturing of the bacterial pathogen associated with citrus greening remains an obstacle to testing Koch’s postulates, and limits the abilities of researchers in the development of molecular methods to study, and reduce citrus greening disease. ARS researchers at Fort Pierce, FL, developed a novel approach to culture these Liberibacter bacteria, by first developing psyllid cell cultures. The bacteria are known to replicate within psyllid tissues, thus this approach combined the knowledge base of pathogen and psyllid biology to produce psyllid cell cultures. A defined medium was developed for establishing psyllid cells and tissues in culture. This timely development was also useful in the propagation of the recently discovered Diaphorina citri reovirus, advancing studies in psyllid viral pathogens.

Review Publications
Ammar, E.D., Gasparich, G.E., Hall, D.G., Hogenhout, S.A. 2011. Spiroplasma-like organisms closely associated with the gut in five leafhopper species (Hemiptera: Cicadellidae). Archives Of Microbiology. 193:35-44.

Hall, D.G., Hentz, M.G. 2011. Seasonal flight activity by the Asian citrus psyllid in east central Florida. Entomologia Experimentalis et Applicata. 139:75-85.

Dogramaci, M., Chen, J., Arthurs, S.P., McKenzie, C.L., Irizarry, F., Houben, K., Brennan, M., Osborne, L. 2011. Mini-aspirator: A new device for collection and transfer of small arthropods to plants. Florida Entomologist. 94(1):22-27.

Last Modified: 8/3/2015
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