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United States Department of Agriculture

Agricultural Research Service


Location: Subtropical Insects and Horticulture Research

2009 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
Seasonal phenology of male flight, synthetic pheromone lure longevity, diel activity patterns and optimal design were described for the pink hibiscus mealybug was clarified using traps baited with a new synthetic sex phereomone.

Advances were made in biological control of the Diaprepes root weevil. Two Caribbean parasitoid species are now established in south Florida. Releases of one parasite species were initiated in Texas.

The physiological and developmental responses of each life stage of the Diaprepes root weevil to low temperatures were used to generate a climate model in collaboration with the Animal and Plant Health Inspection Service (APHIS) to describe the current distribution of Diaprepes and its egg parasitoids in Florida and to predict those regions in other U.S. states that are susceptible to establishment of Diaprepes and its egg parasitoids.

Work was continued to determine the olfactory response of the Diaprepes root weevil to plant and conspecific volatiles in collaboration with ARS scientists at the Chemicals Affecting Insects Behavior Laboratory. A patent was submitted on an attractant based on plant volatiles.

Research on flight activity of the Asian citrus psyllid revealed that the psyllid routinely disperses to and from citrus trees at distances of up to 500 feet. There was evidence that a mass migration of adult psyllids may sometimes occur during spring.

Yellow sticky traps were shown to have value for detecting adult psyllids in citrus and for investigating general population trends, but they were inconsistent indicators of absolute densities.

The Asian citrus psyllid was shown to be tolerant of mild freeze events during the egg, nymph and adult stages.

Tamarixia radiata, a parasite of Asian citrus psyllid, was found to be highly susceptible to a number of pesticides used in Florida citrus.

Progress was made on identifying changes in expression of tomato genes in response to whitefly feeding as the plant matures.

Screened commercially available biocontrol agents for chilli thrips and have found two phytoseiid predatory mites with good efficacy, Amblyseius swirskii and Neoseiulus cucumeris.

A number of pesticides used to manage whiteflies and chilli thrips were screened against predatory mites. Imidacloprid, dinotefuran or spriomesifin generally appeared to be compatible with mites, but a new material (spirotetramat) may interfere with using predatory mites in an Integrated Pest Management program.

Development of method to study salivary sheath formation by the psyllid has resulted in discovery of novel interdiction point. Research on chemical composition of this sheath and how to inhibit its synthesis will be continued.

1. The genome of Liberibacter asiaticus was completely sequenced. This was a project jointly commandeered with the Subtropical Plant Pathology Research Unit at the U.S. Horticultural Research Laboratory in collaboration with a number of USDA-ARS and university researchers. Sequencing the genome allows the scientific community to better understand the bacterium, to identify the bacterium’s enzymatic and metabolic pathways, to understand the bacterium’s nutritional requirements, to determine what makes it pathogenic in citrus, and to determine why it replicates in the Asian citrus psyllid.

2. Distribution of Bemisia tabaci Biotypes in Florida – Investigating the Q Invasion. Development of diagnostic tools for distinguishing different biotypes of silverleaf whitefly facilitated the determination of the whitefly’s distribution in Florida prior to and after the introduction of the devastating Q biotype into the United States. The Q biotype only attacked greenhouse grown ornamental plants and herbs in Florida and had not invaded field-grown vegetables as feared. Three separate Q haplotypes within Florida were discovered that could be used to associate populations known to be related by grower and plant type thereby tracking distribution routes. We determined that biotype Q entered Florida through at least two separate introductions. In-depth analysis of insecticide resistance profiles of different biotype Q populations indicates that different populations have different insecticide resistance profiles; therefore, the ability to identify the Q haplotype is of practical importance to growers by providing information that will improve management decision making with respect to pesticide applications.

3. Novel control method for Asian citrus psyllid through insect feeding disruption. Many phloem feeding insects produce salivary sheaths as they probe the plant tissue in search of phloem cells that are penetrated for the purpose of extracting nutrients from the plant sap. Development of method to study Asian citrus psyllid salivary sheath formation has led to discovery of a way to block the formation of this structure. It is envisioned that, by blocking the ability of the insects to form salivary sheaths as they probe the plant, we will be able to make a plant resistant to psyllid feeding. This method of resistance will be sustainable and biologically based and thus eliminating the need for costly and environmentally damaging chemical pesticides. If such a method is realized, it may be applicable across all phloem feeding insects that produce salivary sheaths: aphids, whiteflies, plant/leafhoppers, mealybugs, psyllids, scales, etc.

4. Improved detection of causative agent of Citrus Greening. As Citrus greening continues to spread in the U.S. there is a need for sensitive and reliable methods of detecting the causative agent: Candidatus Liberibacter asiaticus (CLas). A new more sensitive Q-PCR-based method was developed and used to survey for the presence of CLas in citrus from throughout the U.S. The results show the presence of CLas strains (some of which may not be associated with Greening Disease). Showing the presence of CLas populations that are not associated with Citrus Greening provides a powerful tool in understanding the pathogenic nature of CLas in citrus. Comparison of differences among pathogenic and non-pathogenic strains of CLas can be used to identify important processes in the pathogenicity and this information can be used to develop interdiction strategies.

5. Whitefly Infestation Time Affects the Severity of Tomato Irregular Ripening Disorder. The effect of time of whitefly infestation and the role of nutrition in the development of Tomato Irregular Ripening Disorder associated with silverleaf whitefly feeding and characterized by incomplete ripening of longitudinal sections of fruit was determined. Plants infested with whitefly had significantly higher levels of nutrients in their leaves than in non-infested control plants at final harvest, regardless of time of infestation. Almost all the fruit (99 percent) produced by tomato plants infested with whitefly at the 5 to 7 leaf and flower stages (78 and 56 days of whitefly exposure, respectively) developed the disorder with fruit exhibiting both internal and external symptoms. Plants infested at the green fruit stage (35 days of whitefly exposure) had 79 percent of the fruit develop the disorder. Surprisingly, 58 percent of fruit from plants infested at the red breaking fruit stage (14 days of whitefly exposure) also developed the disorder indicating that tomatoes may need to be protected from silverleaf whitefly until harvest to avoid this disorder.

6. Citrus Leafminer. Field trials using advanced statistical design determined the optimal blend of synthetic sex pheromone components for both attraction of the citrus leafminer, Phyllocnistis citrella, to pheromone-baited traps and disorientation of male moths for the purposes of mating disruption. A binary blend of the natural 3:1 ratio of (Z,Z,E)-7,11,13-hexadecatrienal:(Z,Z)-7,11-hexadecadienal was most effective as an attractant for male moths. However, mating disruption trials revealed that the triene component alone was more effective in disrupting trap catch. While either individual component was effective at disrupting mating in field trials, (Z,Z,E)-7,11,13-hexadecatrienal was approximately 13 times more effective compared with (Z,Z)-7,11-hexadecadienal alone. Use of geometric design and response surface modeling to field studies provided insight into the mechanism of mating disruption and strongly support sensory imbalance as the operating mechanism for this species.

7. Chemical ecology of Diaprepes root weevil. A putative pheromone was identified by gas chromatograph-coupled electroantennography (GC-EAD) for the Diaprepes root weevil. The compound was collected from the head space above male Diaprepes and from male frass, but not from females. The compound is being collected and awaits elucidation of its chemical structure.

8. Diaprepes root weevil. A new artificial was developed for the Diaprepes root weevil. Optimization studies using mixture-amount designs resulted in a greatly simplified and less expensive diet compared to the standard commercial diet that produces adult weevils of a desired weight. It is hypothesized that weevils of normative weight reared on artificial diet are ethologically and physiologically more similar to field-collected weevils compared with the very large weevils produced by the standard commercial diet in use for greater than 20 yrs.

6.Technology Transfer

Number of the New/Active MTAs (providing only)1
Number of Invention Disclosures Submitted1
Number of New Patent Applications Filed1
Number of Other Technology Transfer1

Review Publications
Otalora Luna, F., Hammock, J.A., Alessandro, R.T., Lapointe, S.L., Dickens, J.C. 2009. Host plant kairomones for the tropical weevil Diaprepes abbreviatus. Arthropod-Plant Interactions. 3: 63-73.

McKenzie, C.L., Albano, J.P. 2009. The effect of time of sweetpotato whitefly infestation on plant nutrition and development of tomato irregular ripening disorder. Horticulture Technology. 19(2):353-359.

Shatters, Jr., R.G., Powell, C.A., Boykin, L.M., Sheng, H.L., McKenzie, C.L. 2009. Improved DNA barcoding method for Bemisia tabaci and related Aleyrodidae: Development of universal and Bemisa tabaci biotype-specific mitochondrial cytochrome c oxidase I polymerase chain reaction primers. Journal of Economic Entomology. 102(2):750-758.

Bethke, J.A., Byrne, F.J., Hodges, G.S., McKenzie, C.L., Shatters, Jr., R.G., 2008. First report of the Q biotype of the sweetpotato whitefly Bemisia tabaci in Guatemala. Phytoparasitica. 37:61-64.

Duncan, L.W., Stuart, R.J., Gmitter, F.G., Lapointe, S.L. 2009. Use of landscape fabric to manage Diaprepes root weevil in citrus groves. Florida Entomologist 92:74-79.

Hall, D.G. 2009. An assessment of yellow sticky card traps as indicators of the relative abundance of adult Diaphorina citri in citrus. Journal of Economic Entomology. 102:446-452.

Hall, D.G., Gottwald, T.R., Nguyen, N.C., Ichinose, K., Le, Q.D., Beattie, G.A.C., Stover, E. 2008. Greenhouse investigations on the effect of guava on infestations of Asian citrus psyllid in grapefruit. Proceedings Florida State Horticultural Society. 121:104-109

McKenzie, C.L., Hodges, G.S., Osborne, L., Byrne, F.J., Shatters, R.G. 2009. Distribution of Bemisia tabaci (Hemiptera: Aleyrodidae) biotypes in Florida - Investigating the "Q" invasion. Journal of Economic Entomology. 102(2):670-676.

Shatters, R.G., Hunter, W.B., Hall, D.G., McKenzie, C.L., Duan, Y. 2009. Optimizing a 16S rRNA-based double stranded DNA bindng Q-PCR method for detection of Candidatus Liberibacter species associated with plants and psyllids. Molecular and Cellular Probes.

Arthurs, S., McKenzie, C.L., Chen, J., Dogramaci, M., Brennan, M., Houben, K., Osborne, L.S. 2009. Evaluation of Neoseiulus cucumeris and Amblyseius swirskii (Acari: Phytoseiidae) as biological control agents of Chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae) on pepper. Biological Control. 49(1):91-96.

Flores, D., Hall, D.G., Jenkins, D.A., Setamou, M. 2009. Abundance of Asian citrus psyllid on yellow sticky traps in Florida, Puerto Rico, and Texas citrus groves. Southwestern Entomologist. 34(1):1-11.

Wenninger, E., Stelinski, L.L., Hall, D.G. 2009. The roles of olfactory cues, visual cues, and mating status in orientation of Diaphorina citri Kuwayama (Hemiptera: Psyllidae) to four different host plants. Environmental Entomology. 38:225-234.

Hunter, W.B., Dowd, S.E., Katsar, C., Shatters, Jr., R.G., McKenzie, C.L., Hall, D.G. 2009. Psyllid biology: Expressed genes in adult Asian citrus psyllids, Diaphorina citri. The Open Entomology Journal. 3:18-29.

Lapointe, S.L., Hall, D.G. 2009. Arrestment behavior in the polyphagous tropical root weevil Diaprepes abbreviatus. Journal of Economic Entomology. 102(3):992-998.

Hert, M., Hunter, W.B., Katsar, C.S., Sinisterra, X.H., Hall, D.G., Katsar, C.S., Powell, C.A. 2009. Reovirus-like sequences isolated from adult Asian citrus psyllid, (Hemiptera: Psyllidae: Diaphorina Citri). Florida Entomologist. 92:314-320.

Last Modified: 4/24/2014
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