The Star variety had the numerically highest numbers of total eggs and larvae per plant compared with any other variety. The likelihood ratio chi-square test indicated a significant effect of egg count on the top third of the plant as well as a significant effect of larval count on the two plant locations, i.e. the top third also having the highest count . More eggs were found on the top third of the blueberry plants and there was a higher percent of larvae present on the top third of the plant ,regardless of plant variety. However, in the choise test, the Star variety had the highest percent of eggs found and larvae present. The Snowchaser variety had the lowest numbers of thrips counted overall, with fewer eggs, larvae and adults collected on that variety. The Misty variety had fewer larvae present than eggs laid and the number eggs laid were comparable to levels on Emerald.Under the conditions of these trials , citrus thrips egg hatch typically would take place within 4-9 days , therefore numbers of motile insects counted in both studies would be larvae from the first generation and surviving adults. The primary focus of this work was to determine if there was a difference in the number of eggs laid on the different types plants and our data clearly show this was the case . The no-choice oviposition test showed that the highest number of eggs and larvae were found on citrus and sumac and the blueberry varieties Star and Jewel. Intermediate levels were found on Emerald and Misty, round plant pot and the lowest numbers on Snowchaser and O’Neal. The highest numbers of larvae present in clipcages were on the citrus, sumac and Star blueberry variety.
The Tukey HSD separation for total counts of eggs and larvae group Jewel with the citrus, sumac, and Star, but these data may be skewed due to the negative correlation between the number of eggs laid on the Jewel variety and the number of larvae present.The choice oviposition test also showed a correlation between the number of eggs located and the number of larvae present on the plant. Evaluation of count means showed a difference in citrus thrips numbers on the Star variety over the other blueberry varieties in the test. When given the choice to move about the plants, the citrus thrips’ activities at the time of isolation and counting appear to be similar for Emerald and O’Neal with a mean of less than 10 adults recovered from those plants. In the choice oviposition tests, the negative correlation between egg and larval counts is also apparent for the Jewel variety. Some explanations for this negative correlation could be: first instars eclosing from the egg suffered high mortality, the larvae did not or cannot feed and/or develop well on this variety, and/or the larvae dispersed away from the plant onto other plants. If the latter were the case, then one would expect to see one or more other blueberry varieties with higher numbers of larvae present, but that was not the case and given the fact the canes did not remain in contact with one another, it is unlikely that high levels of larval dispersion to different pots took place.
There are several possibilities which explain the results: 1) females chose to lay eggs preferentially in some varieties over others, 2) egg survivorship influenced the numbers counted/found, 3) first instar egg eclosion varied across variety, 4) differential larval survivorship and development on the plants, and 5) larval dispersion, possibly to other plants, but possibly off the plants with mortality ensuing in unevaluated portions of the bug dorm. The Chi-square values for plant location were significant indicating that there were disparate numbers of eggs laid and larvae counted between the two locations, with the top third of the plants, regardless of variety, preferentially chosen over the bottom two-thirds. This was likely due to the amount of flush growth present on the top third of the plants. Also, given data in our studies, thrips activities appear higher on the top third of the plant; this is likely a good area to sample when looking for thrips on blueberries. Combining all the data, our studies clearly show that the Star variety had more citrus thrips than the other blueberry varieties, and numbers of oviposited eggs found on Star, Jewel, citrus and sumac were similar. This quite possibly is due to Star’s parentage. The Star variety is a variety that produces flowers the earliest and for the longest period during the season and while yield may not be as high as some of the other varieties, it is planted as a season long fruit bearer. Because the highbush blueberries are hybrids of one another and the nurseries have proprietary rights to the genetics of these varieties, we are therefore unsure how closely related the varieties we tested are. Snowchaser was the variety least preferred by the citrus thrips based on our data, however, to our knowledge it is not a variety currently grown commercially in California.
There are countless factors that need to be considered to fully understand insect host choice, including but not limited to, host plant finding, host plant acceptance, host plant relatedness, resource concentration, resource availability and host use . The insect’s ability to locate the host plant, settle, feed, reproduce and successfully produce the next generation that achieves reproductive maturity involves countless steps and subtle interactions that are beyond the scope of the work presented here. We provide a platform for further work on the distribution, abundance and avenues for research related to citrus thrips as a pest of blueberries in California. We anticipate citrus thrips will remain a pest of concern to the blueberry industry of California as the industry continues to expand.The role of a public university such as the University of California is to improve the human condition through research, teaching, and public service. At the Center for Agroecology and Sustainable Food Systems we strive to meet the ideals of a public university by working to improve ecological sustainability and social justice in the food and agriculture system. Our work is multifaceted, covering a spectrum that includes research , education and public service . The Center provides a unique academic and practical forum for exploring alternative visions for food and agriculture, and pursues a research and education agenda that is broader than most agriculture—even sustainable agriculture—programs. The Center works to give special attention to the silent voices in sustainable agriculture. This includes conceptual work that expands the way in which sustainability is defined so that it addresses political economic and social justice issues related to class, ethnicity, and gender . Empirical research at the Center also addresses these issues through projects that focus on fair trade, farm labor issues, round garden pot and alternative agrifood institutions. The Center’s broad agenda is enabled by specific historical factors and constrained by the same conditions that affect all public universities.Several factors have converged to make our broad agenda possible: the Center’s location in a social sciences division on an interdisciplinary, non-land-grant campus; the incorporation of practitioners and academics on our staff; and the concentration of nongovernmental organizations in the region focused on sustainable agriculture, the environment and family farms. The Center is housed within the Division of Social Sciences at a campus that does not have an agriculture school. This unconventional setting is probably what enabled the Center to pioneer work in sustainable food systems and organic agriculture at a time when mainstream agriculture campuses were vehemently opposed to these ideas. It also makes possible the development of a strong social science research program to complement the natural science work, which is unusual in a program focused on food and agriculture. This hybrid structure has enabled us to combine basic and applied research within and across disciplines, as well as provide research support and outreach programs for multiple partners and audiences. This provides a fluid, mutual “reality check” on theoretical and applied work.
Practitioners provide academics with ideas and questions that need to be addressed, along with practical information, experience, and feedback on the relevance of research to the community in question. In turn, academics provide practitioners with new information, research support, and a broader context for their work and understanding of the agrifood system. In addition to its work with graduate and undergraduate students, the Center works with nontraditional students through nonformal education programs. For example, the Apprenticeship program provides experiential training on gardening and farming techniques, small farm viability, marketing, social justice, and the environmental impacts of agriculture to nontraditional students. The Center has also developed a collaborative arrangement with a local NGO that provides training and education programs in Spanish to Latino farmers and farm workers in the Central Coast region. The Center’s work with these kinds of organizations is facilitated by a fortuitously high density of sustainable agriculture nongovernmental organizations in the Santa Cruz region, such as the California Sustainable Agriculture Working Group , the Community Alliance with Family Farmers, the California Certified Organic Farmers, and the Organic Farming Research Foundation. The geographical proximity between the Center and these organizations facilitates joint research and education projects, as well as the kinds of casual interactions that build networks. In addition, a project funded by the U.S. Department of Agriculture has strengthened the work of a multidisciplinary team of researchers and fostered collaborations with County, State and Federal agencies, local NGOs, Farm Bureaus, Cooperative Extension and researchers in other UCSC departments and other institutions. Thus, the Center’s history and location make it well situated for fulfilling the academic and service missions of a public university. However, challenges remain. A primary issue is how to provide service to the nontraditional students and underserved members of the public. In particular, how can programs that serve groups considered marginal to the traditional research and education of the university agenda secure adequate resources for their work? Ironically, some of the programs for which the Center is renowned are also those that face the greatest challenges.Many of the same factors that have enabled the Center to pursue a whole-systems, progressive agenda have also constrained our ability to have legitimacy among conventional agricultural institutions and resulted in considerable uncertainty in funding and support from year to year. In particular, being outside of the land grant system with no major agriculture program on campus presents both funding challenges and limits the recognition of our work A key issue is how to effectively serve the scope of “publics” who have the right to claim resources of a public university. The Center prioritizes working with community groups that have largely been outside of the traditional agricultural extension frame, including organic farmers, food security groups, and food-system workers. While working with a diversity of farmers, including those typically underserved by mainstream agriculture programs such as those with limited capital and small-scale organic growers, has been a priority for the Center as well as for other sustainable agriculture programs, even this emphasis is skewed relative to their numbers among agrifood system workers. Of those who work in the agrifood sector, 78 percent work in food processing, retailing, and distributing; 11 percent supply inputs such as equipment and agrichemicals. Only 11 percent are farmers and farm workers directly involved in agricultural production. In California most of those who are involved in farming are hired farm workers. In California there are 18 farm workers for each farmer, and hired farm workers perform at least 80 percent of all the farm work in the state . How can research and education programs do a better job of addressing the needs of low-capital and small-scale farmers, farm workers, food industry workers, and consumers? This is much more challenging than working with the traditional producer clients of agricultural universities. The most disadvantaged and impoverished may not have the time and resources to participate in committee meetings and actions or actively engage with participatory or community-based research processes . In addition, working with these groups may alienate more traditional clients. For example, credibility with growers is a major issue for sustainable agriculture programs that include social issues as a priority in their research agendas.