Progress 02/01/09 to 02/01/14
Outputs Target Audience: Results from the Temecula Valley insect monitoring and disease surveys have been presented to vineyard owners in the Southern Central Valley and and in Riverside and San Diego Counties. Moreover this research has been included in presentations to the Pierce's Disease Control Program, and Southern California pest control advisers. Finally aspects of this work have been presented to academic researchers in seminars and research symposia. Over the past year presentations of the vector behavior work were made to the Pacific Branch of the Entomological Society of America, the Entomological Society of America, and the Ecological Society of America. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Over the last year the project, especially the third objective, included various forms of training and professional development. This work on vector behavior involved the participation of a postdoctoral researcher, who gained valuable training epidemiological modeling methods. He also expanded his professional development by presenting the results of that research at multiple scientific conferences. The laboratory portion of that project also provided the opportunity for three undergraduates to gain experience with insect behavior and molecular pathogen detection. How have the results been disseminated to communities of interest? Over the last year, the results related to pathogen spread (Objective 1) were presented to stakeholder groups via a series of presentations and online resources. This includes presentations to Southern California pest control advisers. I also participated, at the request of the Taiwanese government, in a symposium on Pierce’s disease ecology and management that featured this research. The results of Temecula Valley areawide monitoring for glassy-winged sharpshooters continue to be report on a regular basis to stakeholders via an e-mailed newsletter and on the Temecula GWSS blog (http://cisr.ucr.edu/temeculagwss/) and were presented at the Pierce’s Disease Research Symposium and the Temecula Valley Grape Day. For the effects of climate (Objective 2), presentations were made to academic audiences at the Pacific Branch meeting of the Entomological Society of America and the American Phytopathological Society of America on the role of climate in mediate sharpshooter dynamics and risk of disease spread. For the vector behavior and potato psyllid/Zebra chip disease work (Objective 3), results have been included in several presentations to the general public, entomological associations, and pest control advisors on the role of invasive vectors in driving outbreaks of animal and plant pathogens. This research was also the basis for presentations to academic audiences at the Entomological Society of America, Pacific Branch of the Entomological Society of America, and the Ecological Society of America annual meetings. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts What was accomplished under these goals?
Over the last year the primary focus was on the third objective, vector behavior and its implications for pathogen transimission. For this objective a set of epidemiological modeling was completed, the results of which were described in a journal article that is now in press. Additionally, undergraduates working in the lab completed additional sets of behavioral bioassays for the potato psyllid (Bactericera cockerelli) and its response to Zebra chip diseased-plants, caused by the bacterial pathogen Candidatus Liberibacter psyllaurous. The other two objectives were completed the previous year; although together those objectives led to the publication of two journal articles and two proceedings this past year.
Publications
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2014
Citation:
Zeilinger, A., Daugherty, M.P. Vector preference and host defense against infection interact to determine disease dynamics. Oikos. In press
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2014
Citation:
Rathe, A.A., Pilkington, L.J., Hoddle, M.S., Spohr, L.J., Daugherty, M.P., and G.M. Gurr 2014. Feeding and development of the glassy-winged sharpshooter, Homalodisca vitripennis, on Australian native plant species in the USA and implications for Australian biosecturity. PLoS One, In press.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Rashed, A., Kwan, J., Baraff, B., Ling, D., Daugherty, M.P., Killiny, N., and R.P. P. Almeida, 2013. Relative susceptibility of Vitis vinifera cultivars to vector-borne Xylella fastidiosa through time. PLoS One 8:e55326
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Gruber, B., Daugherty, M. 2013. Predicting the effects of seasonality on the risk of pathogen spread in vineyards: vector pressure, natural infectivity, and host recovery. Plant Pathology 62:194-204.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Rathe, A., Pilkington, L., Gurr, G., Hoddle, M., Daugherty, M., Constable, F., Luck, J., Powell K., Fletcher, M., and O. Edwards. 2012. Incursion preparedness: anticipating the arrival of an economically important plant pathogen Xylella fastidiosa Wells (Proteobacteria: Xanthomonadaceae) and the insect vector Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) in Australia. Australian Journal of Entomology 51:209-220.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Daugherty, M.P. 2013. How effective is sharpshooter control at limiting Pierce's disease spread in California vineyards? Proceedings of the International Symposium on Insect Vectors and Insect-borne diseases. 12p.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Daugherty, M.P. 2013. Linking within-vineyard sharpshooter control to Pierce's disease spread. Pierce's Disease Control Program. p.3. Pierce's Disease Research Progress Reports. Pierce's Disease Control Program
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Progress 01/01/13 to 09/30/13
Outputs Target Audience: Results from the Temecula Valley insect monitoring and disease surveys have been presented to vineyard owners in the Southern Central Valley and and in Riverside and San Diego Counties. Moreover this research has been included in presentations to the Pierce's Disease Control Program, and Southern California pest control advisers. Finally aspects of this work have been presented to academic researchers in seminars and research symposia. Over the past year presentations of the vector behavior work were made to the Pacific Branch of the Entomological Society of America, the Entomological Society of America, and the Ecological Society of America. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Over the last year the project, especially the third objective, included various forms of training and professional development. This work on vector behavior involved the participation of a postdoctoral researcher, who gained valuable training epidemiological modeling methods. He also expanded his professional development by presenting the results of that research at multiple scientific conferences. The laboratory portion of that project also provided the opportunity for three undergraduates to gain experience with insect behavior and molecular pathogen detection. How have the results been disseminated to communities of interest? Over the last year, the results related to pathogen spread (Objective 1) were presented to stakeholder groups via a series of presentations and online resources. This includes presentations to Southern California pest control advisers. I also participated, at the request of the Taiwanese government, in a symposium on Pierce’s disease ecology and management that featured this research. The results of Temecula Valley areawide monitoring for glassy-winged sharpshooters continue to be report on a regular basis to stakeholders via an e-mailed newsletter and on the Temecula GWSS blog (http://cisr.ucr.edu/temeculagwss/) and were presented at the Pierce’s Disease Research Symposium and the Temecula Valley Grape Day. For the effects of climate (Objective 2), presentations were made to academic audiences at the Pacific Branch meeting of the Entomological Society of America and the American Phytopathological Society of America on the role of climate in mediate sharpshooter dynamics and risk of disease spread. For the vector behavior and potato psyllid/Zebra chip disease work (Objective 3), results have been included in several presentations to the general public, entomological associations, and pest control advisors on the role of invasive vectors in driving outbreaks of animal and plant pathogens. This research was also the basis for presentations to academic audiences at the Entomological Society of America, Pacific Branch of the Entomological Society of America, and the Ecological Society of America annual meetings. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts What was accomplished under these goals?
Over the last year the primary focus was on the third objective, vector behavior and its implications for pathogen transimission. For this objective a set of epidemiological modeling was completed, the results of which were described in a journal article that is now in press. Additionally, undergraduates working in the lab completed additional sets of behavioral bioassays for the potato psyllid (Bactericera cockerelli) and its response to Zebra chip diseased-plants, caused by the bacterial pathogen Candidatus Liberibacter psyllaurous. The other two objectives were completed the previous year; although together those objectives led to the publication of two journal articles and two proceedings this past year.
Publications
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2014
Citation:
Zeilinger, A., Daugherty, M.P. Vector preference and host defense against infection interact to determine disease dynamics. Oikos. In press
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2014
Citation:
Rathe, A.A., Pilkington, L.J., Hoddle, M.S., Spohr, L.J., Daugherty, M.P., and G.M. Gurr 2014. Feeding and development of the glassy-winged sharpshooter, Homalodisca vitripennis, on Australian native plant species in the USA and implications for Australian biosecturity. PLoS One, accepted.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Rashed, A., Kwan, J., Baraff, B., Ling, D., Daugherty, M.P., Killiny, N., and R.P. P. Almeida, 2013. Relative susceptibility of Vitis vinifera cultivars to vector-borne Xylella fastidiosa through time. PLoS One 8:e55326
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Gruber, B., Daugherty, M. 2013. Predicting the effects of seasonality on the risk of pathogen spread in vineyards: vector pressure, natural infectivity, and host recovery. Plant Pathology 62:194-204.
- Type:
Journal Articles
Status:
Published
Year Published:
2012
Citation:
Rathe, A., Pilkington, L., Gurr, G., Hoddle, M., Daugherty, M., Constable, F., Luck, J., Powell K., Fletcher, M., and O. Edwards. 2012. Incursion preparedness: anticipating the arrival of an economically important plant pathogen Xylella fastidiosa Wells (Proteobacteria: Xanthomonadaceae) and the insect vector Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) in Australia. Australian Journal of Entomology 51:209-220.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Daugherty, M.P. 2013. How effective is sharpshooter control at limiting Pierce's disease spread in California vineyards? Proceedings of the International Symposium on Insect Vectors and Insect-borne diseases. 12p.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Daugherty, M.P. 2013. Linking within-vineyard sharpshooter control to Pierce's disease spread. Pierce's Disease Control Program. p.3. Pierce's Disease Research Progress Reports. Pierce's Disease Control Program.
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Progress 01/01/12 to 12/31/12
Outputs OUTPUTS: Over the past year I completed one project and continued an additional field study related to this subject. Over the past year I also developed further epidemiological models to describe the significance of vector behavior for plant disease dynamics, and I initiated a new set of studies in an additional system, Potato psyllid (Bactericera cockerelli) response to Zebra chip disease, caused by the bacterial pathogen Candidatus Liberibacter psyllaurous. The first of these concerned a three year study of Pierce'd disease spread in Temecula Valley vineyards. The second project is an ongoing monitoring program for the invasive vector, the Glassy-winged sharpshooter in Temecula Valley region. Thus far deliverables include an improved understanding of Pierce's disease epidemiology, with implications for refinements to disease management, that have been presented to stakeholder groups via a series of presentations and online resources. Aspects of this work were discussed during presentations to Temecula Valley grape growers in the Spring of 2012, at CAPCA laws and regulations seminars, and to Los Angeles-area grape growers in the summer. Related work was also featured in a presentation to the Entomological Association of Southern California on the role of agricultural-urban interfaces in complicating the management of invasive insects. Finally, the results of Temecula Valley areawide monitoring for glassy-winged sharpshooters continue to be report on a regular basis to stakeholders via an e-mailed newsletter and on the Temecula GWSS blog (http://cisr.ucr.edu/temeculagwss/). For the vector behavior and potato psyllid/Zebra chip disease work, results have been included in several presentations to the general public, entomological associations, and pest control advisors on the role of invasive vectors in driving outbreaks of animal and plant pathogens. This research was also the basis for presentations to academic audiences at the Entomological Society of America and UC Riverside's Center for Disease Vector Research Symposium. PARTICIPANTS: Rodrigo Almeida, UC Berkeley; Arash Rashed, UC Berkeley; Tracy Pinckard, UC Riverside; Frank Byrne, UC Riverside; Adam Zeilinger, UC Riverside TARGET AUDIENCES: Results from the Temecula Valley insect monitoring and disease surveys have been presented to vineyard owners in Kern and Tulare Counties, and Riverside and San Diego Counties. Moreover this research has been included in presentations to the San Bernardino County Master Gardener's program. Finally aspects of this work have been presented to academic researchers in seminars and research symposia. Presentations of the vector behavior work so far were made to the Southern California Entomological Society, Pacific Branch of the Entomological Society of America, Entomological Society of America, and UC Riverside's Center for Disease Research Symposium. Moreover, this work has been featured in presentations to the general public. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts If the glassy-winged sharpshooter Homalodisca vitripennis readily promotes secondary spread then even relatively low populations can cause severe outbreaks, necessitating additional control measures - including insecticide application within vineyards and vigorous roguing of infected vines. However, if H. vitripennis spreads the pathogen in a primary manner, then area-wide programs may be sufficient to maintain losses below economic thresholds without any additional control measures. Results from a recently completed study in Temecula, CA relate to the effectiveness of within-vineyard chemical control at limiting Pierce's disease spread. Estimates of imidacloprid concentrations differed greatly between regularly treated, intermittently treated, and untreated vineyards, indicating that our categorization of fields based on prior treatment history was accurate. Regarding Pierce's disease in vineyards, results so far suggest that regular or even intermittent imidacloprid applications result in lower disease prevalence than for vineyards which did not receive any imidacloprid treatments within the last few years. Yet, estimates of year-to-year changes in prevalence between Fall 2010 and Fall 2012 were universally low, regardless of treatment. This is consistent with sharpshooter trap catches in vineyards which were low overall and did not differ greatly as a function of insecticide treatment regime. Finally, differences in insecticide treatments in vineyards does not appear to be affecting the abundance of natural enemies in vineyards - natural enemy and secondary pest abundance were no higher in treated versus untreated fields. The results of season-long monitoring of sharpshooter populations in citrus as part of an areawide control program suggest that populations have been intermediate compared to past years. Although there was a late season peak in trap catches due to unseasonably warm weather in September, mid-Summer peaks in population were a fraction of what they have been in 2008 and 2009, but also higher than 2010 and 2011. Epidemiological theory predicts that differences in vector preference based on host infection status (i.e. healthy or infected) affects disease dynamics. Over the last year I developed further models to explore the interaction between vector behavior and host plant resistance or tolerance to a pathogen. Results from those analyses suggest that tolerant host plant types can act as sources of pathogen spread, especially if vectors prefer healthy plants. Resistant plant types, however, tend to result in lower rates of pathogen spread regardless of vector preference. Laboratory behavioral bioassays were conducted with Potato psyllid adults to determine whether they distinguish between healthy, insect damaged, and infected tomato plants. The preliminary results from those trials indicate that psyllids preferentially orient to infected plants over healthy and especially insect-damaged plants. This behavior may explain in part why this insect is efficient at promoting spread of Zebra chip disease.
Publications
- Daugherty, M.P., Gruber, B.R., Almeida, R.P.P., Anderson, M.M., Cooper, M.L., Rasmussen, Y.D., and E.A. Weber 2012. Testing the efficacy of barrier plantings for limiting sharpshooter spread. American Journal of Enology and Viticulture 63:139-143.
- Daugherty, M.P., and T. Pinckard. 2012. Riverside County glassy-winged sharpshooter program in the Temecula Valley. Pp. 20-22. 2012 Pierces Disease Research Progress Reports. Pierce's Disease Control Program.
- Daugherty, M.P., Pinckard, T., Zeilinger, A., Davenport, S., Toscano, N., and F. Byrne. 2012. Linking within-vineyard sharpshooter management to Pierces disease spread. pp.23-28. 2012 Pierce's Disease Research Progress Reports. Pierce's Disease Control Program.
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Progress 01/01/11 to 12/31/11
Outputs OUTPUTS: Objective 1: Estimate the importance of sharpshooter vine-to-vine (i.e. secondary) spread of the pathogen, Xylella fastidiosa. A prior field experiment suggested a modest ability of the glassy-winged sharpshooter to promote pathogen spread. This past year we continued a set of disease surveys in 34 Temecula Valley vineyards that are intended to address the same question at a larger scale. Estimates of vine infection rate in each vineyard were compared to the previous season to determine how much spread is occurring. In addition, we monitored vector populations over the course of the season. Finally, we quantified the concentration of insecticide (i.e. imidacloprid) in each of the vineyards and natural enemy abundance. These surveys are intended to 1) estimate rates of pathogen spread by the glassy-winged sharpshooter at the vineyard scale, and 2) evaluate the impact of imidacloprid applications on insect abundance (vectors and natural enemies) and pathogen spread. Objective 2: Evaluate the effect of climate (i.e. local environmental temperature) on Xylella fastidiosa spread and Pierce's disease severity. Last year my lab group completed a multisite field study that is investigating the role of local climate in driving infection dynamics. To evaluate this we established a natural field climate gradient study at sites between Southern California and Oregon. Groups of vines at these different sites were infected with X. fastidiosa at different times throughout the growing season, then we measured infection levels in vines over the season and again the following year. The within-season infection level data has been completed. The overwinter recovery rates will be estimated this coming year by retesting all initially infected vines. Objective 3: Quantify sharpshooter preference for X. fastidiosa-infected versus healthy vines and its implications for transmission and pathogen spread. Prior greenhouse and field behavioral trials indicate that sharpshooters consistently avoid strongly symptomatic grapevines - with the invasive glassy-winged sharpshooter showing similar behavior to native sharpshooters. Grapevines are notably in that different species and cultivars differ in Pierce's disease severity, suggesting there is variability among cultivars in resistance or tolerance to the pathogen Xylella fastidiosa. Over the last year I've begun to evaluate what these potential differences in resistance or tolerance might mean for disease spread. Specifically, I developed a single patch epidemiological compartment model with a latently-exposed host stage and a vector-host contact rate function that includes a symptom preference/avoidance weighting. Relative differences in resistance or tolerance were simulated, compared to a truly susceptible host type, by making different assumptions regarding incubation rate (i.e. transition from the latent to infected stage) and the proportion of infected hosts that act as asymptomatic "carriers." Disease incidence in hostplants and vectors were simulated under different scenarios for the strength of vector preference/avoidance of symptoms and host resistance/tolerance to the pathogen. PARTICIPANTS: The field experiments measuring disease spread included effort by Matt Daugherty (UC Riverside, PI), postdoctoral researcher Adam Zeilinger, and SRA Tracy Pinckard. The climate work included effort by Matt Daugherty (UC Riverside, PI) and his postdoc, Barrett Gruber. The vector behavior modeling was conducted by Matt Daugherty (UC Riverside, PI). TARGET AUDIENCES: Results from the Temecula Valley insect monitoring and disease surveys have been presented to vineyard owners in Kern and Tulare Counties, and Riverside and San Diego Counties. Moreover this research has been included in presentations to the San Bernardino County Master Gardener's program. Finally aspects of this work has been presented to academic researchers in seminars and research symposia. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts The threat posed by the glassy-winged sharpshooter has been argued to stem from its ability, unlike native sharpshooters, to promote vine-to-vine spread of X. fastidiosa. However, results from our Temecula Valley Pierce's disease surveys (Obj. 1) indicate thus far that this insect is not that efficient at promoting spread. Disease prevalence differed among vineyards, with lower prevalence on average in sites that are either regularly or intermittently treated with imidacloprid. But year-to-year change in prevalence (i.e. spread) was extremely low (i.e. not appreciably greater than zero) regardless of treatment regime. This result is consistent with a prior study and is important because it suggests that as long as glassy-winged sharpshooter populations are suppressed, via area-wide control programs, it is unlikely that we'll see the magnitude of disease outbreaks that occurred in Southern California approximately 10 years ago. I have featured these results in presentations to grower groups and the general public, because they factor into future Pierce's disease management programs. The results from the climate work (Obj. 2), thus far, are unclear regarding whether climate is an important factor in determining the severity of Pierce's disease in different grapevine growing regions of the Western U.S. Within-season infection levels measured in Riverside, CA, Davis, CA, and Corvallis, OR did not differ appreciably among sites despite large differences in growing season temperatures. Yet results for the effect of climate on overwinter recovery rate are as yet incomplete. I expect that more infected vines in Corvallis will recover compared to Davis and, especially, Riverside. The results from the vector behavior modeling (Obj. 3) suggest that there are interactive effects of vector preference based on host symptom status and host resistance versus tolerance to a pathogen. In general host resistance should reduce rates of spread. However, tolerant varieties or species may act as sources of pathogen spread - especially if vectors strongly discriminate against symptomatic hosts. These results suggest that identifying whether grapevine varietals are truly resistant versus being tolerant to X. fastidiosa infection is important for proper disease management.
Publications
- Gruber, B.R., and M.P. Daugherty 2012. Predicting the effects of seasonality on the risk of pathogen spread in vineyards: vector pressure, natural infectivity, and host recovery. Plant Pathology, accepted. Daugherty, M.P., Rashed, A., Almeida, R.P., and T. Perring 2011. Vector preference for host infection status: sharpshooter movement and Xylella fastidiosa transmission. Ecological Entomology 36:654-662.
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Progress 01/01/10 to 12/31/10
Outputs OUTPUTS: Objective 1: Estimate the importance of sharpshooter vine-to-vine (i.e. secondary) spread of the pathogen, Xylella fastidiosa, at different times of the year. My lab group measured rates of X. fastidiosa secondary spread in field cages that were exposed to GWSS at different times during the growing season. Vines were tested for infection multiple times over two growing seasons to estimate acute versus chronic infection as a function of grapevine variety and timing of inoculation. Patterns of acute secondary spread showed a trend towards being higher at the later inoculation dates. However, the scale of acute spread is notably low - between 8 and 13% depending on the timing of vector introduction. Overwinter recovery rate also depended on timing of infection. 60% of vines that became infected in early September recovered over the winter whereas none of the plants infected in early June or mid-July recovered. These results suggest that there may be a slightly higher rate of acute secondary spread occurring later in the year, which makes biological sense because the needle inoculated vines should be highly infectious later in the season, facilitating spread. Overwinter recovery seems to enhance the "seasonality signal" with respect to patterns of chronic infection by eliminating late season infections. But, the expected mid-season peak in chronic secondary spread is notably absent. The absence of this peak is perhaps not surprising given the low overall rates of acute secondary spread. Objective 2: Evaluate the effect of climate (i.e. local environmental temperature) on Xylella fastidiosa spread and Pierce's disease severity. Last year my lab group completed a transmission experiment that measured the efficiency of two sharpshooter species at transmitting X. fastidiosa when held at different temperatures. The results from this experiment show that inoculation efficiencies of both the blue-green sharpshooter and the glassy-winged sharpshooter depended on temperature, with the highest transmission rates occurring at the highest temperature. The other, ongoing, project related to this issue concerns how local climate drives infection dynamics. To evaluate this we've established a natural field climate gradient study at sites between Southern California and Oregon. Groups of vines at these different sites are being infected with X. fastidiosa at different times throughout the growing season, then we are measuring infection levels and overwinter recovery rates. Objective 3: Quantify sharpshooter preference for infected versus healthy vines and its implications for the transmission function. I conducted a field trial that evaluated whether sharpshooters distinguish between healthy and X. fastidiosa infected grapevines. Sharpshooters were confined in sleeve cages with canes from a healthy and infected vines, and I noted regularly their position. All three species spent significantly more time on healthy branches, indicating that indeed they avoid Pierce's disease vines. These results are the foundation for further work looking at vector behavior and what it means for pathogen spread. PARTICIPANTS: The field experiments measuring disease spread included effort by Matt Daugherty (UC Riverside, PI), and two collaborators: Rodrigo Almeida (UC Berkeley) and Jennifer Hashim-Buckey (UC Cooperative Extension). Daugherty designed the experiment and collected most of the data. Almeida and Hashim-Buckey helped with experiment setup and secured additional funding. In addition Daugherty's SRA, Tracy Pinckard helped with sample processing at the end of the experiment. The climate work included effort by Matt Daugherty (UC Riverside, PI) and his postdoc, Barrett Gruber. Daugherty designed and collected all data for the transmission work. Gruber is currently collecting data on the field climate gradient experiment. The vector behavior work included effort by Matt Daugherty (UC Riverside, PI) in collaboration with Tom Perring (UC Riverside). Daugherty and Perring collected the field data. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts The threat posed by the glassy-winged sharpshooter has been argued to stem from its ability, unlike native sharpshooters, to promote vine-to-vine spread of X. fastidiosa. However, the dynamics of pathogen infections within vines is believed to vary seasonally, which may constrain rates of vine-to-vine spread. We found evidence that overwinter recovery plays a role in chronic spread, but evidence for seasonality affecting acute spread was relatively weak. More importantly, the overall rates of vine-to-vine spread were low, between 8 and 13%. Arguably these rates of spread are too low, in isolation, to explain the impact of the glassy-winged sharpshooter that has been observed in the past. Thus it may be necessary to invoke other factors to explain the impact of this vector in California vineyards. This result is important because it suggests that as long as glassy-winged sharpshooter populations are suppressed, via area-wide control programs, it is unlikely that we'll see the magnitude of disease outbreaks that occurred in Southern California approximately 10 years ago. I have featured these results in presentations to grower groups and the general public, because they factor into future Pierce's disease management programs. The results from the climate work, thus far, suggest that climate may be an important factor in determining the severity of Pierce's disease in different grapevine growing regions of the Western U.S. The ongoing research will further elucidate the role of climate for this disease system with the ultimate goal being to generate predictions for the likely impact of future climate warming, which is predicted for the region, on disease dynamics. The results from the vector behavior work, thus far, indicate that sharpshooter preferentially feed on healthy grapevines. This result is notable because, according to epidemiological theory, such behavior should generally limit rates of disease spread. Ongoing work on this project is investigating how differences among grapevine varieties in their resistance or tolerance to X. fastidiosa infection, plus vector preferences for infection status. The goal is to determine the feasibility of finding and using resistant varieties to limit disease spread in particularly high risk regions.
Publications
- Daugherty, M.P., Bosco, D. and Almeida, R.P.P. 2009. Temperature mediates vector transmission efficiency: inoculum supply and plant infection dynamics. Annals of Applied Biology 155:361-369.
- Daugherty, M.P., Lopes, J.R.S. and Almeida, R.P.P. 2010. Vector within-host feeding preference mediates transmission of a heterogeneously distributed pathogen. Ecological Entomology 35:360-366
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