Progress 10/01/12 to 09/30/17
Outputs
Target Audience:I have two primary target audiences. The first is the community of farmers and pest management professionals who are responsible for pest management activities in California agriculture on a day-to-day basis. The second is the community of professional researchers who develop the knowledge and new methods for improving pest management practice. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?One undergraduate (Felipe Andreazza) who was an exchange student from Brazil; three graduate students (Matthew Meisner, Nicholas Booster, and Michael Culshaw-Maurer); and two postdoctoral researchers (Asaf Sadeh and Tobin Northfield) all pursued research and received training in experimental design, data collection and analysis, and manuscript preparation under this project. How have the results been disseminated to communities of interest?Our results have been disseminated to communities both through extension-type publications (e.g., the new pest management volume for grapes published by University of California Statewide IPM program) and through publications in scientific journals. We have also given many presentations at scientific meetings reporting the results of our work. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The main goal of our project is to enhance the use of natural biological control of insect pests as an alternative to the widespread use of insecticides. To do this, one of our main research objectives is to understand natural factors that act to limit the efficacy of biological control agents (i.e., predatory and parasitic insects). Why don't these natural enemies always generate effective control of pest insects? If we can understand what factors impose limits on the efficacy of biological control agents, we can then ask if we can "fix" those problems, and thereby improve natural pest control. During this 5-year project, we worked on two different cropping systems to determine what was limiting the effectiveness of biological control. First, we worked on a generalist predator, Geocoris pallens, which is an important biological control agent in several important crops, including cotton, alfalfa, strawberries, potatoes, and many others. It can suppress populations of thrips, aphids, whiteflies, spider mites, caterpillars -- the list is long. In California cotton, however, we found that populations of Geocoris seem to run up against an upper "ceiling" -- that is, populations rise when prey availability is high, but they will only go so high and no higher, even when prey are super-available. We discovered that cannibalism is the main barrier to population growth for Geocoris: once the populations get high enough, cannibalism becomes so intense that populations simply will not grow any further. In some cases, this allows pest populations (and especially spider mite populations) to escape from control. Furthermore, over the past five years, we have conducted surveys across California that have revealed surprisingly large amounts of variation in the expression of cannibalism: in some populations, most females exhibit strong restraint from cannibalizing conspecific eggs, but in other populations some females will eat nearly 100% of the eggs that they encounter over a 3-day assay period. We are still trying to understand the basis for the elevated expression of cannibalism, but it appears that a transmissible element is involved. We are currently characterizing a community of viruses that we have discovered infecting Geocoris pallens to determine which may be the ultimate cause of the high cannibalism populations. In the field, the highly cannibalistic populations have shown dramatic collapses, leading to loss of biological control. In some cases the collapsed populations have recovered after a period of a few years; in other cases, the populations have not recovered, even after a period of >10 years. We still have much to learn about this interaction. We have also built mathematical and simulation models to help us understand the interactions of pathogens and cannibalism. We have found that, contrary to the conventional belief, that cannibalism can, under some conditions, lead to rapid spread of pathogens through host populations. This is especially true for vertically-transmitted pathogens. We have also found that a pathogen that elicits elevated expression of cannibalism in infected hosts can cause dramatic suppression of its host population, as we have found for Geocoris pallens. Our second project focused on natural control of a complex of three leafhopper pests in California grape vineyards: the grape leafhopper (Erythroneura californica), the variegated leafhopper (Erythroneura variegata), and the Virginia creeper leafhopper (Erythroneura ziczac). These leafhoppers are major pests in vineyards, causing defoliation, sunburn of grapes, and interfering with harvest. The most important biological control agents of these leafhoppers are minute egg parasitoids found in the genus Anagrus, including primarily Anagrus daanei and Anagrus erythroneurae. Anagrus parasitoids are extremely abundant in grape vineyards, and contribute to control of leafhoppers. Again, however, control is often incomplete, and farmers are motivated to apply insecticides to suppress leafhopper densities. What factors limit the efficacy of Anagrus. Our earlier work showed that sulfur, which is used widely to control powdery mildew in grapes, is both highly persistent in vineyards and highly toxic to Anagrus. Thus, switching to less toxic fungicides will likely improve leafhopper control by parasitoids. Second, during this review period we found that Anagrus spp. are very frequently limited by the availability of sugar-rich foods: without sugar in their diet, which is normally obtained by feeding on floral nectar, Anagrus starve to death within just a few hours of emerging as adults. Most vineyards are managed to have a "clean" floor, meaning that herbicides, tilling, and mowing remove nearly 100% of flowering plants from the vineyard. In these vineyards, Anagrus collected in the field were shown, through biochemical assays of gut contents, to have low to zero access to sugar meals. Thus, one step that farmers can take to improve biological control of leafhoppers is to (a) eliminate sulfur use, and (b) plant flowering cover crops, or tolerate flowering weeds, in the vineyard. We also explored other factors that limit reproductive success by Anagrus parasitoids. We found that larger parasitoids achieve higher reproductive success, and that some parasitoids do exhaust their lifetime supply of mature eggs (these parasitoids emerged with a fixed complement of mature eggs, and cannot mature any more). Although Anagrus parasitoids have evolved increased fecundity in agricultural sites (compared with their native habitats in riparian plant communities in California), egg limitation remains as a limit on reproductive success for these minute parasitoids.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Meisner, M. H., T. Zaviezo, and J. A. Rosenheim. 2017. Landscape effects on Lygus hesperus densities, cotton yield, and pesticide use. Pest Management Science 73:232-239.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Rosenheim, J. A., and C. Gratton. 2017. Ecoinformatics (Big Data) for agricultural entomology: pitfalls, progress, and promise. Annual Review of Entomology 62:399-417.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Lichtenberg, Elinor M., Christina M. Kennedy, Claire Kremen, P�ter Bat�ry, Frank Berendse, Riccardo Bommarco, Nilsa A. Bosque-Perez, Lu�sa G. Carvalheiro, William E. Snyder, Neal M. Williams, Rachel Winfree, Faye Benjamin, Claire Brittain, Rebecca Chaplin-Kramer, Yann Clough, Heather Connelly, Brian Danforth, Tim Diek�tter, Sanford Eigenbrode, Johan Ekroos, Elizabeth Elle, Breno Freitas, Yuki Fukuda, Hannah Gaines, Claudio Gratton, Andrea Holzschuh, Rufus Isaacs, Marco Isaia, Shalene Jha, Dennis Jonason, Vincent P. Jones, Bj�rn Klatt, Alexandra Klein, Jochen Krauss, Deborah Letourneau, Sarina Macfadyen, Rachel Mallinger, Emily Martin, Eliana Martinez, Jane Memmott, Lora Morandin, Lisa Neame, Sandra �berg, Mark Otieno, Mia Park, Lukas Pfiffner, Michael Pocock, Carlos Ponce, Simon Potts, Katja Poveda, Mariange Ramos, Jay A. Rosenheim, Maj Rundl�f, Hillary Sardi�as, Manu Saunders, Nicole Schon, Amber Sciligo, C. Sheena Sidhu, Ingolf Steffan-Dewenter, Teja Tscharntke, Milan Vesel�, Wolfgang Weisser, Julianna Wilson, David W. Crowder. 2017. A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes. Global Change Biology 23:4946-4957.
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Progress 10/01/15 to 09/30/16
Outputs
Target Audience:Our target audience is the community of farmers, pest management consultants, and applied researchers in the agricultural sciences who are using or developing biological pest controls. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project represented a collaboration between four visiting scientists: Dr. Michal Segoli (Ben Gurion University, Israel), Dr. Dori Nava (EMBRAPA, Brazil), Dr. Madelaine Venzon (EPAMIG, Brazil), and Dr. Angelo Pallini (Universidade Federale de Vicosa, Brazil). How have the results been disseminated to communities of interest?Analysis is currently underway, with writing to follow. What do you plan to do during the next reporting period to accomplish the goals?We expect the data analysis and writing to progress during the next reporting period. We will also be working on biological pest control in California citrus production, where we will assess the contributions of Euseius spp. predatory mites to the biological control of two key pests on citrus: the citrus red mite, Panonychus citri and the citrus thrips, Scirtothrips citri.
Impacts
What was accomplished under these goals?
During this review period, a visiting scientist from Israel, Dr. Michal Segoli, came to UC Davis to conduct intensive field work during the summer of 2016. A study was conducted comparing life history traits of Anagrus spp. parasitoids in replicate agricultural and natural plant communities. Parasitoids were reared from host material and either held to quantify longevity (with versus without sugar provided as a supplemental food) and fecundity (assessed through dissections to quantify egg load). Analysis of the dataset is underway. We also conducted work on biological pest control in California citrus. Using an ecoinformatics approach, we assembled a database on commercial citrus production that included data on densities of two key pests, citrus red mite Panonychus citri, and citrus thrips, Scirtothrips citri, as well as one of the important predators of these pests, predatory Euseius spp. mites.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Tscharntke, T., D. Karp, R. Chaplin-Kramer, P. Bat�ry, F. deClerck, C. Gratton, L. Hunt, A. R. Ives, M. Jonsson, A. Larsen, A. Martin, A. Martinez-Salinas, T. D. Meehan, M. ORourke, K. Poveda, J. A. Rosenheim, A. Rusch, N. Schellhorn, T. C. Wanger, S. Wratten, and W. Zhang. 2016. When natural habitat fails to enhance biological pest control Five hypotheses. Biological Conservation 204:449-458.
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Progress 10/01/14 to 09/30/15
Outputs
Target Audience:Our target audience for this work is biological control practitioners in general, and pest management professionals working in commercial grape vineyards. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?An undergraduate student, Felipe Andreazza, was mentored in an independent research project, which during this reporting period included final manuscript preparations, responding to Editors and peer reviewers, revising a manuscript, and completing the publication process. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?We are currently planning a large 'common garden' experiment in which we will compare the longevity and fecundity of A. erythroneurae and A. daanei that are collected from low- and high-host density sites and then reared in a laboratory setting with intermediate host availability.
Impacts
What was accomplished under these goals?
In this reporting period, we continued to explore factors that limit the reproductive success of parasitoids in the genus Anagrus. The first project examined the importance of body size on realized lifetime reproductive success (number of eggs laid) by Anagrus sophiae, which attacks Prokelisia spp. planthoppers in Spartina saltmarshes. We found that body size is positively and linearly related to reproductive success in nature. Because we were able to measure lifetime eggs laid in the field, this is one of the few direct assessments of the importance of body size for parasitoid fitness in nature. The second project focused on Anagrus erythroneurae, which is a key biological control agent of three leafhopper pests (western grape leafhopper, variegated leafhopper, and Virginia creeper leafhopper) of cultivated grapes. Previous work had demonstrated substantial variation in fecundity of A. erythroneurae populations collected at sites that varied in host density. In particular, parasitoids collected from riparian habitats, where generally low-density populations of leafhoppers feed on the native plant Vitis californicus, have relatively low fecundities (10-20 eggs produced total). In contrast, parasitoids collected from agricultural sites, where higher densities of leafhoppers feed on cultivated grapes, Vitis vinifera, often have much higher fecundities (30-40 eggs produced total). We sought to determine if these differences could be generated through phenotypic plasticity. In particular, we tested whether the host density experienced by the mother could influence the fecundity of her daughters. (This was a relevant hypothesis to test, because A. erythroneurae is strictly proovigenic, with all eggs matured during the pupal stage. Thus, it was hard to imagine how the daughter's experience with host availability could influence her fecundity.) We found no evidence for this form of transgenerational phenotypic plasticity. Instead, preliminary evidence suggests that significant variation occurs between different families in fecundity. Ongoing work will explore whether or not this is an example of rapid, contemporary evolution in response to changing conditions in agriculture.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Segoli, M., and J. A. Rosenheim. 2015. The effect of body size on the oviposition success of a minute insect parasitoid in nature. Ecological Entomology 40:483-485
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Andreazza, F., and J. A. Rosenheim. 2015. Absence of transgenerational phenotypic plasticity in fecundity in the parasitoid Anagrus erythroneurae (Hymenoptera: Mymaridae). Journal of Insect Science 15(1):138. (DOI: 10.1093/jisesa/iev122).
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Progress 10/01/13 to 09/30/14
Outputs
Target Audience: This project aims to make short-term improvements in pest management and agricultural productivity. Thus, the primary target audience is farmers and the community of pest management professionals, including private consultants, who support their pest management decision making. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? One graduate student is completing his PhD working on this project and developing methods for using farmer- and consultant-generated data to address a broad array of questions in agricultural entomology ("Ecoinformatics"). How have the results been disseminated to communities of interest? I co-organized a Program Symposium at the national meeting of the Entomological Society of America to consider the progress, pitfalls, and promise of ecoinformatics methods of research in agricultural entomology. What do you plan to do during the next reporting period to accomplish the goals? Additional papers on the landscape ecology of Lygus colonization of cotton fields and optimal management schemes for Lygus are still being developed.
Impacts
What was accomplished under these goals?
Colonization of crops by pests and natural enemies can be influenced by both (1) the surrounding landscape of crop fields, and (2) the crop fields grown in the area the previous year(s), i.e., crop rotation effects. We have been analyzing the influence of current- and previous-year crop field landscapes on the colonization of cotton fields by the key pest Lygus hesperus and effects on yield. We have found statistically significant effects on both pest densities and yield. Interestingly, crops such as alfalfa that have been viewed as positive, because of their potential to act as trap crops for Lygus and simultaneously as a 'nurse crop' for many beneficial insects may be helpful as current-year neighbors, but harmful as previous-year neighbors. Much of the influence of neighboring crops seems to be driven by Lygus colonization dynamics; further work is needed to elucidate the role of natural enemies.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Meisner, M. H., and J. A. Rosenheim. 2014. Ecoinformatics reveals effects of crop rotational histories on cotton yield. PLOS ONE 9(1):e85710.
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Progress 01/01/13 to 09/30/13
Outputs
Target Audience: The target audience is farmers in the western region of the United States, along with pest control consultants, and state and university researchers in the biocontrol community. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Postdoctoral researcher Michal Segoli conducted work during this review period and received professional training in data analysis and manuscript preparation. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals? We expect to test whether the changing fecundity in Anagrus species is a genetic effect versus a case of phenotypic plasticity. We also plan to use ecoinformatics methods ('mining' of pre-existing agricultural data) to analyze the contribution of biological control to overall pest management in California citrus.
Impacts
What was accomplished under these goals?
During this time period, we completed a study that set out to determine what factor(s) might limit the ability of Anagrus erythroneurae and Anagrus daanei to function as effective biological control agents of the grape leafhopper in California grape vineyards. We also examined the impact of these parasitoids on two other leafhoppers, the variegated leafhopper and the newly invading Virginia creeper leafhopper. Our studies established three major findings. First, we discovered that parasitoids may frequently be limited by the unavailability of sugar-rich resources, such as floral nectar, in commercial vineyards. Biochemical assays for sugar-rich meals in parasitoid guts demonstrated that most parasitoids lacked access to nectar. Shortages of sugar-rich foods worsened as the season progressed. Given that sugar is a requirement for Anagrus spp. parasitoids to live more than a single day, this seems likely to represent an important limit to the efficacy of these parasitoids. Second, we found that approximately 10-15% of all parasitoids fully exhaust their lifetime complement of eggs in the field (they are "egg limited"). This was, however, observed only in vineyards that had not been treated with sulfur. (Previous work had demonstrated that sulfur, which is used on almost 100% of California grape acreage, is highly toxic to Anagrus, and prevents females from living long enough to lay all their eggs.) Larger females had higher lifetime reproductive success, and reproductive success was also higher at vineyards that harbored higher density populations of the grape leafhopper host. Third, we found that Anagrus fecundity appears to be changing in response to local availability of leafhopper hosts. At sites where leafhoppers were abundant, Anagrus parasitoids emerged with a larger lifetime complement of eggs. This contrast also suggested that Anagrus parasitoids found in riparian plant communities, where the native Vitis californica is common, generally have lower host availability than do Anagrus parasitoids that have colonized agricultural vineyards. Correspondingly, parasitoids from riparian sites emerge with fewer eggs. Still remaining to be determined is whether the changes in parasitoid fecundity represents an example of contemporaneous evolution associated with moving from natural to agricultural settings, or whether instead it represents some sort of transgenerational phenotypic plasticity.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Segoli, M., and J. A. Rosenheim. 2013. Spatial and seasonal variation in sugar availability for insect parasitoids in agricultural fields and consequences for reproductive success. Biological Control 67:163-169.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Segoli, M., and J. A. Rosenheim. 2013. The link between egg production and host density in a parasitoid insect: comparison among agricultural and natural habitats. Functional Ecology 27:1224-1232.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Segoli, M., and J. A. Rosenheim. 2013. Limits to the reproductive success of two insect parasitoid species in the field. Ecology 94:2498-2504.
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: My stakeholders include researchers and biocontrol practitioners in California and the US more broadly. Research results have been disseminated in a publication (see below), in extension talks, and in presentations at scientific meetings and seminars given in universities across the country. PARTICIPANTS: We partnered with the USDA-ARS laboratory in Maricopa, Arizona for this project. Training was provided to two technicians (Lea Bateman and Lindsey Hack) and four Ph.D. students (Frances Sivakoff, Matthew Meisner, Katelyn Zemenick, and Billy Krimmel). TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Key impacts of my work during 2012 were primarily focused on control of Lygus species in California cotton. A general finding is that biological control of Lygus species in California cotton may not always generate good suppression of damaging populations. We demonstrated that this is not a result of out-dispersing its natural community of predators (see publication listed below). We showed that cotton is surprisingly sensitive to yield loss generated by Lygus herbivory early during the fruiting season (during June on pre-flowering cotton). During this period, growers have been losing considerable yield without knowing it. In contrast, during July (flowering period), growers manage Lygus very aggressively, but we have shown that cotton can compensate fully for moderate damage during this period. Thus, we have made two primary recommendations: (1) growers should be more conservative in their use of pesticides during July, and (2) growers should be more vigilant in controlling early season Lygus. In a series of meetings with farmers, we explained the results of our analyses. Growers responded with immediate changes in their management practices.
Publications
- Sivakoff, F. J., J. A. Rosenheim, and J. Hagler. 2012. Relative dispersal ability of a key agricultural pest and its predators in an annual agroecosystem. Biological Control 63:296-303.
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Results have been disseminated in a series of talks given to groups of state and federal researchers, as well as researchers within the university academic community. Publications are also being completed. PARTICIPANTS: We partnered with the USDA-ARS laboratory in Maricopa, Arizona for this project. Training was provided to one undergraduate student (Collin Edwards) and two Ph.D. students (Frances Sivakoff and Yao Hua Law). TARGET AUDIENCES: This project will dovetail with a large, multi-PI project funded by the USDA-RAMP project. That project has a large and formal outreach component, involving extensive grower training. The results of this project are helping to provide the basic knowledge underlying these outreach/grower training efforts. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
All of the work reported here was conducted in California cotton. The work led to several recommendations for farmers and consultants regarding how best to manage pest populations in cotton. First, we found that by clustering cotton fields, pest damage generated by Lygus hesperus can be reduced. We also identified neighboring fields that were associated with higher Lygus densities (e.g., safflower, oats, grapes, onion, uncultivated agricultural fields) and some that were identified with substantially reduced Lygus densities (alfalfa, cotton). This can help farmers to 'design' the layout of fields within their ranches to reduce the severity of Lygus infestation and the need for costly and disruptive pesticide applications. Second, we found that Geocoris pallens, which has been used extensively in augmentative biological control, have limits to their efficacy that are imposed due to their intense cannibalism. Finally, we quantified the impact of generalist predators on survival of another commercial biological control agent, the common green lacewing. These results have changed the way these biological control agents are used in California cotton.
Publications
- Sivakoff, F. J., J. A. Rosenheim, and J. Hagler. 2011. Using protein marking to study insect long distance dispersal. Methods in Ecology and Evolution 2:77-85.
- Law, Y. H., and J. A. Rosenheim. 2011. Effects of combining an intraguild predator with a cannibalistic intermediate predator on a species-level trophic cascade. Ecology 92:333-341.
- Lucas, E., and J. A. Rosenheim. 2011. Influence of extraguild prey density on intraguild predation in Heteroptera: a review of the evidence and a case study. Biological Control 59:61-67.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Results have been disseminated in a series of talks given to groups of state and federal researchers, as well as researchers within the university academic community. Publications are also being completed (some are in press, others in revision; these will be reported next year, since they were not published during 2010). PARTICIPANTS: We partnered with the USDA-ARS laboratory in Maricopa, Arizona for this project. Training was provided to one undergraduate student (Collin Edwards), one Ph.D. student (Frances Sivakoff), and one postdoctoral researcher (Moran Segoli). TARGET AUDIENCES: This project will dovetail with a large, multi-PI project funded by the USDA-RAMP project. That project has a large and formal outreach component, involving extensive grower training. The results of this project are helping to provide the basic knowledge underlying these outreach/grower training efforts. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
A key outcome or impact of our work is a specific set of guidelines for farmers growing cotton regarding how they should arrange fields within their ranches to minimize the impact of a potentially devastating insect pest, Lygus. By clustering cotton fields together, we have shown that Lygus damage can be substantially reduced. Lygus does not disperse more rapidly than its key natural enemies, so they do not escape from biological control in large areas of cotton monoculture. But, because Lygus mobility is modest, and because Lygus does not reproduce rapidly on cotton (a relatively low quality host), we have shown that clustering fields results in lower pest densities, less crop damage, and a reduced need to apply insecticides to suppress Lygus populations.
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: The main communities of interest are (1) the cotton farming, (2) professional pest management consultants, and (3) researchers working at universities and state governmental agencies who are implementing biological control. I reach these audiences in by making presentations at meetings (for the cotton community, primary by attending the annual meeting of the California State Support Board of Cotton Incorporated and by attending various annual meetings of workgroups organized by the University of California Division of Agriculture and Natural Resources); for the PCA community, by giving talks at small meetings, such as the annual meeting of the Association of Applied IPM Ecologists. In addition, written publications are important in reaching UC cooperative extension personnel and researchers and consultants outside of academia. PARTICIPANTS: The primary collaborator on this project was a Ph.D. candidate, Yao Hua Law. The project supported his research and professional development as a senior Ph.D. student. TARGET AUDIENCES: The target audiences are (1) the cotton farming community, (2) professional pest management consultants, and (3) researchers working at universities and state governmental agencies who are implementing biological control programs. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Progress during 2009 has demonstrated that cotton can compensate for herbivory by Lygus during much of the growing season, as long as densities stay in the low-moderate range. The predators Geocoris pallens and Zelus renardii are the most important agents keeping Lygus in check. Constructive impacts from this work are focused mainly in the area of how farmers manage key arthropod pests of cotton. Through face-to-face meetings with influential growers, we are providing a new management plan for Lygus that uses less pesticides and relies more heavily on natural control and plant compensation.
Publications
- No publications reported this period
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: The communities of interest are (1) the cotton farming community (including farmers, pest control advisors, and cooperative extension personnel), and (2) researchers working at universities and state governmental agencies who are implementing biological control programs. I reach these audiences in by making presentations at meetings (for the cotton community, primary by attending the annual meeting of the California State Support Board of Cotton Incorporated and by attending various annual meetings of "workgroups" organized by the University of California Division of Agriculture and Natural Resources). In addition, written publications are important in reaching UC cooperative extension personnel and researchers and consultants outside of academia. PARTICIPANTS: The project that culminated in one of the publications listed above (de Valpine and Rosenheim) involved a long-term collaboration between two campuses within the University of California system (Berkeley and Davis). TARGET AUDIENCES: The target audiences are (1) the cotton farming community (including farmers, pest control advisors, and cooperative extension personnel), and (2) researchers working at universities and state governmental agencies who are implementing biological control programs. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Constructive impacts from this work are focused mainly in the area of how farmers manage key arthropod pests of cotton. In particular, our work demonstrates that one dominant generalist predator (Geocoris pallens) can suppress populations of nymphal Lygus hesperus. This knowledge allows farmers to withhold applications of pesticides to control Lygus in fields where high density populations of Geocoris are present. Our work also has demonstrated that populations of the cotton aphid are highly volatile and hard to predict, even in the short-term. This has emphasized the need for farmers to be vigilant, monitoring their aphid populations regularly, and being ready to intervene if damaging populations develop.
Publications
- Zink, A. G., and J. A. Rosenheim. 2008. Stage-specific predation on Lygus hesperus affects its population stage structure. Entomologia Experimentalis et Applicata 126:61-66.
- de Valpine, P., and J. A. Rosenheim. 2008. Field-scale roles of density, temperature, nitrogen, and predation on aphid population dynamics. Ecology 89:532-541.
- Rosenheim, J. A., S. J. Jepsen, C. E. Matthews, D. S. Smith, and M. R. Rosenheim. 2008. Time limitation, egg limitation, the cost of oviposition, and lifetime reproduction by an insect in nature. American Naturalist 172:486-496.
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Progress 01/01/07 to 12/31/07
Outputs
The goal of this regional research project is to enhance the efficacy of biological control of key insect and weed pests in the western United States. My laboratory's work on this project during 2007 was conducted in two areas. First, in collaboration with four other scientists, my laboratory conducted a formal meta-analysis of the experimental literature on intraguild predation. Intraguild predation occurs when two predators that potentially compete for a shared resource (prey species) also engage in predator-prey interactions with each other. The meta-analysis revealed that in terrestrial arthropod communities, intraguild predation tends to weaken the overall ability of predators to suppress populations of herbivores. There was, however, a large amount of variability between studies: in some cases, adding an intraguild predator improved biological control, whereas in other cases adding an intraguild predator weakened biological control. A key predictor of the effect
of adding an intraguild predator was how effective each of the predators was as a control agent of the herbivore when tested singly. In particular, when the 'intermediate predator' was a very effective biological control agent, adding an intraguild predator was often highly disruptive of control (leading to increases in herbivore density). Second, my laboratory studied the reproductive ecology of a gall midge RHOPALOMYIA CALIFORNICA which has been used as a biological control agent of invasive BACCHARIS SPP. in Australia. We documented that this midge matures all of its eggs before emerging as an adult and does not resorb eggs, even if deprived of suitable oviposition sites. Females emerged primarily in the morning and laid their eggs and died all within the first day of their emergences.
Impacts
Our work helps to inform biological control practitioners about what species to introduce when building a new community of control agents to suppress invasive herbivores. Our results suggest that intraguild predators should be scrutinized very carefully before being introduced to a new region as part of a biological control program.
Publications
- Rosenheim, J. A. 2007. Intraguild predation: new theoretical and empirical perspectives. Ecology 88: 2679-2680.
- Vance-Chalcraft, H. D., J. A. Rosenheim, J. R. Vonesh, C. W. Osenberg, and A. Sih. 2007. The influence of intraguild predation on prey suppression and prey release: a meta-analysis. Ecology 88:2689-2696.
- Rosenheim, J. A., S. J. Jepsen, C. E. Matthews, D. S. Smith, and M. R. Rosenheim. 2007. Portrait of an ephemeral adult stage: egg maturation, oviposition, and longevity of the gall midge Rhopalomyia californica. Annals of the Entomological Society of America 100: 549-561.
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Progress 01/01/06 to 12/31/06
Outputs
The goal of this regional research project is to enhance the efficacy of biological control of key insect and weed pests in the western United States. My laboratory's work on this project during 2006 was conducted in four areas. (1) First, we continued to explore the role of GEOCORIS PALLENS as a biological control agent of LYGUS HESPERUS in cotton. We demonstrated experimentally that GEOCORIS does not suppress populations of mid- or late-instar LYGUS nymphs or adults, but does suppress densities of the youngest LYGUS nymphs. This may be a reflection of feeding on LYGUS eggs. This result is critical in explaining previous observations, made at the scale of large commercial cotton fields, that LYGUS age structure was significantly correlated with the density of GEOCORIS present. (Fields with heavy GEOCORIS populations had a higher ratio of adult:nymphal LYGUS.) These changing age distributions have confounded pest management consultants, because the nymphal stages are
not readily sampled using standard sweep nets, and therefore represent a 'hidden' source of potentially severe crop damage. Thus, fields that lack high GEOCORIS populations may harbor large populations of difficult to detect, but damaging, nymphal LYGUS. (2) Second, we worked in collaboration with Dr. Perry de Valpine (UC Berkeley) to fit models to time series data on the biological control of cotton aphids in cotton by a complex of generalist predators. This work is shedding light on which of these predators is actually making substantial contributions to aphid population suppression under natural, unmanipulated conditions in the field. (3) Third, I am a member of a 5-investigator team that is working to evaluate the effects of intraguild predators on the suppression of shared prey populations. We have completed a meta-analysis that demonstrates that intraguild predators have substantial potential to disrupt the biological control of herbivore populations, and that this potential is
greatest when (a) the intraguild predation is bidirectional, and (ii) the intermediate predator is itself a highly effective biological control agent. (4) Finally, we have initiated a project to assess the impact of the symbiotic bacterium WOLBACHIA on its insect host's lifetime reproductive success. WOLBACHIA generate parthenogenesis when they infect many haplo-diploid parasitoid wasps. Parthenogenesis may in theory enhance the efficacy of some parasitoid biocontrol agents, but only if the WOLBACHIA is not pathogenic (virulent). We are attempting to produce the first estimates of WOLBACHIA virulence in nature (an extensive literature exists on WOLBACHIA effects on host fitness under laboratory conditions, but it is difficult to extrapolate these results to field conditions).
Impacts
Our work on biological control of LYGUS by GEOCORIS is helping farmers to manage LYGUS populations with reduced amounts of pesticides. Our work on intraguild predation will assist researchers who are introducing novel biological control agents to North America to make good decisions on which species to import. Finally, our work on WOLBACHIA will inform future decisions regarding whether or not WOLBACHIA should be excluded during biological control importations.
Publications
- Nelson, E.H., and J.A. Rosenheim. 2006. Encounters between aphids and their predators: the relative frequencies of disturbance and consumption. Entomologia Experimentalis et Applicata 118:211-219.
- Langellotto, G.A., J.A. Rosenheim, and M.R. Williams. 2006. Assessing trophic interactions in a guild of primary parasitoids and facultative hyperparasitoids: stable isotope analysis. Oecologia 150:291-299.
- Rosenheim, J.A., and J.P. Harmon. 2006. The influence of intraguild predation on the suppression of a shared prey population: an empirical reassessment. In: J. Brodeur and G. Boivin (eds.), Trophic and Guild Interactions in Biological Control, Springer, New York.
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Progress 01/01/05 to 12/31/05
Outputs
The goal of this project is to improve biological control programs in agroecosystems through an improved understanding of the ecology of predator-prey and parasitoid-host interactions. During 2005, work was focused in three areas. (1) First, we worked on developing a better understanding of biological control of the western tarnished plant bug, LYGUS HESPERUS, in California cotton. Cotton hosts a diverse community of predators, and we analyzed two years of survey data (approximately 20 time-series in all) to identify predators that might be responsible for stable variation in the densities and age structure of LYGUS populations. We discovered that big-eyed bugs, GEOCORIS spp., are negatively correlated with the proportion of LYGUS populations made up of nymphs. GEOCORIS spp. appear to prey selectively on nymphs (adults are too big to be captured). Because nymphs are damaging, and because nymphs are often poorly sampled by routine scouting of fields, GEOCORIS may play
a particularly important role in suppressing cryptic but damaging populations of nymphs. Ongoing work is assessing the importance of different factors that may constrain the population growth rate of GEOCORIS in cotton fields. (2) Second, we conducted a series of observational studies, field bioassays, and manipulative field experiments to understand the impact of sulfur, which is applied to vineyards to suppress powdery mildew, on biological control of grape leafhoppers, ERYTHRONEURA ELEGANTULA, by parasitoids in the genus ANAGRUS. We discovered that although short-term bioassays suggest that sulfur is highly toxic to ANAGRUS, sulfur has little effect on reproductive success of parasitoids in the field, and no detectable effect on the ability of ANAGRUS to impose mortality on leafhopper populations. It may be that even in the absence of sulfur, other factors place major constraints on the ability of ANAGRUS to function as a good biocontrol agent. Improvements in biological control
may therefore require the simultaneous removal of multiple constraining factors from vineyards. (3) Finally, we conducted a meta-analysis of the effects of intraguild predation on the success or failure of biological control. Contrary to the conventional wisdom, it appears that adding an intraguild predator to a 2-species predator-prey module can have diverse effects: biological control may be improved or disrupted, or there may be little overall effect. Ongoing work is attempting to understand what factors shape the type of result that is observed.
Impacts
IMPACT (Limit to 400 characters): Our work on GEOCORIS is motivating growers to incorporate predator densities into their decision rules regarding when they should apply pesticides to control LYGUS in cotton, thereby decreasing pesticide use. On the longer term, our work is helping to produce a solid basic understanding of natural enemy ecology upon which ecologically sound biological control programs can be developed within an IPM framework.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
The goal of this project is to improve biological control programs in agroecosystems through an improved understanding of the ecology of predator-prey and parasitoid-host interactions. Work published during this review period covered a diverse array of research activities. First, working in California cotton, my colleagues and I have demonstrated that large-scale augmentative releases of the predatory mite GALENDROMUS OCCIDENTALIS are ineffective for control of spider mites. This lack of efficacy stems from the inability of GALENDROMUS OCCIDENTALIS to establish and build large populations in cotton, apparently a result of intense intraguild predation imposed by a group of hemipteran predators. Second, working with NABIS, a predator of pea aphids in alfalfa, we have demonstrated that the impact of a predator on the population growth rate of its prey can be generated through two complementary pathways: (i) first, and most obviously, predators eat prey; and (ii) second,
and less obviously, predators elicit from prey a variety of anti-predator behaviors, and these behaviors may be quite costly, reducing reproduction. In this system, the relative importance of these two pathways was roughly equivalent, a very surprising result for this terrestrial ecosystem. Third, in papaya grown in Hawaii, biological control of the spider mite TETRANYCHUS CINNABARINUS by the predatory mite PHYTOSEIULUS MACROPILIS was shown to be insensitive to the presence of an intraguild predator, the spider NESTICODES RUFIPES. This spider had previously been shown to disrupt biological control of spider mites by another predator, the beetle STETHORUS SIPHONULUS. PHYTOSEIULUS seems to avoid predation by the spider simply by having a very low level of mobility across the leaf surface. This low mobility is achievable simply because PHYTOSEIULUS is small relative to the body size of its spider mite prey, and therefore it does not need to move much across the leaf surface to harvest
many prey. Finally, I constructed a game theory model to explore how the presence of top predators may shape the habitat selection 'games' played by herbivores and their intermediate predators. The model showed that a key prediction of earlier models, in which the spatial distribution of herbivores fails to match the spatial distribution of their host plant resources, is overturned when the model is expanded to include the top predators.
Impacts
In the short term, our work is helping farmers determine when they can rely on effective biological control from naturally-occurring predators, and when they instead need to intervene with other control measures to prevent significant crop damage. On the longer term, our work is helping to produce a solid basic understanding of natural enemy ecology upon which ecologically sound biological control programs can be developed within an IPM framework.
Publications
- Colfer, R.G., J.A. Rosenheim, L. D. Godfrey, and C. L. Hsu. 2004. Evaluation of large-scale releases of western predatory mite for spider mite control in cotton. Biological Control 30:1-10.
- Rosenheim, J.A., D.D. Limburg, R.G. Colfer, V. Fournier, C.L. Hsu, T.E. Leonardo, and E.H. Nelson. 2004. Herbivore population suppression by an intermediate predator, Phytoseiulus macropilis, is insensitive to the presence of an intraguild predator: an advantage of small body size? Oecologia140: 577-585.
- Nelson, E.H., C.E. Matthews, and J.A. Rosenheim. 2004. Predators reduce prey population growth by inducing changes in prey behavior. Ecology 85: 1853-1858.
- Rosenheim, J.A. 2004. Top predators constrain the habitat selection games played by intermediate predators and their prey. Israel Journal of Zoology 50:129-138.
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Progress 01/01/03 to 12/31/03
Outputs
The goal of this project is to improve biological control programs in agroecosystems through an improved understanding of the ecology of predator-prey and parasitoid-host interactions. We are working in two agroecosystems: cotton grown in California and papaya grown in Hawaii. In cotton, we are analyzing the reasons underlying the frequent failure of natural enemies to regulate populations of spider mites, TETRANYCHUS spp., which can defoliate cotton plants and severely reduce yields. There are at least four groups of natural enemies, GALENDROMUS OCCIDENTALIS, FRANKLINIELLA OCCIDENTALIS, ORIUS TRISTICOLOR, and GEOCORIS spp., each of which when tested singly displays strong potential for suppressing spider mite populations. We are investigating the hypothesis that a size-based ladder of intraguild predation, wherein larger predators eat and suppress populations of smaller predators, is responsible for the failure of biological control. We have shown experimentally that
ORIUS and GEOCORIS strongly suppress populations of GALENDROMUS, largely excluding them from cotton. GEOCORIS also strongly suppresses ORIUS. Ongoing work will explore other aspects of the ecology of these complex interactions. In the papaya system, we are working on biological control of the carmine spider mite TETRANYCHUS CINNABARINUS. We have conducted extensive experimentation with early-season augmentative releases of the predator PHYTOSEIULUS MACROPILIS for control of the carmine spider mite. We have found highly mixed results, primarily because the resident natural enemy population (including both PHYTOSEIULUS and the predatory beetle STETHORUS SIPHONULUS) often overwhelmed the beneficial effects of the augmentative releases. Thus, it may be at least as important to conserve naturally-present populations of biological control agents as to conduct augmentative releases. Conservation may need to focus on reducing the use of pesticides in papaya for control of other pests,
including sulfur for powdery mildew and acaricides and insecticides for control of rust mites, scale insects, and leafhoppers.
Impacts
We are helping farmers reduce their reliance on pesticides and maximize their use of natural biological control. In California cotton, we have found that natural controls may be unreliable, and that therefore selective use of acaricides is appropriate. In papaya, in contrast, natural control is quite effective, and growers are encouraged to eliminate pesticide use to the extent possible.
Publications
- Rosenheim, J. A., and J. Brodeur. 2002. A simple trap to study small-scale movement by walking arthropods. Entomologia Experimentalis et Applicata 103:283-285.
- Fournier, V., J. A. Rosenheim, M. W. Johnson, and J. Brodeur. 2003. Augmentative releases of predatory mites on papaya in Hawaii: failure and success. Pages 167-175 in: R. G. Van Driesche (ed.), Proceedings of the International Symposium on Biological Control of Arthropods. Honolulu, Hawaii, 14-18 January 2002, United States Department of Agriculture, Forest Service, Morgantown, WV, FHTET-2003-05, 573 p.
- Colfer, R. G., J. A. Rosenheim, L. D. Godfrey, and C. L. Hsu. 2003. Interactions between the augmentatively released predaceous mite Galendromus occidentalis (Acari: Phytoseiidae) and naturally occurring generalist predators. Environmental Entomology 32:840-852.
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Progress 01/01/02 to 12/31/02
Outputs
The goal of this project is to improve the efficacy of biological control efforts in agroecosystems through an improved understanding of the ecology of predator-prey and parasitoid-host interactions. We are working in two agroecosystems: cotton grown in California and papaya grown in Hawaii. In cotton, we are continuing to analyze data on food web structure and function in the cotton ecosystem, with a particular focus on the functional significance of predator-predator interactions. In particular, we have demonstrated that highly asymmetrical predator-prey interactions may underlie strong `cascading' effects of predators on prey in the species-rich cotton ecosystem. Thus, generalist predators may receive only a small amount of their total food intake from any given prey species, but they may still impose very strong mortality on some of those prey species. In the papaya system, we are working on biological control of the two key folivorous arthropods, the carmine
spider mite TETRANYCHUS CINNABARINUS and the papaya leaf edgeroller mite CALACARUS BRIONESAE. We have found that the leaf edgeroller mite, which was recently introduced to Hawaii, has essentially no natural enemies (parasitoids or predators), and builds up populations that accelerate leaf senescence, retard papaya growth, and reduce yield. The carmine spider mite, in contrast, has several associated specialist predators that can be effective as biological control agents. A generalist predator in the system, the web-building spider NESTICODES RUFIPES, can disrupt this biological control by consuming the specialist predators. We have explored these interactions using both manipulative field experiments and computer simulation models, and demonstrated that the foraging mode of the predators are a key determinant of whether or not predators contribute to spider mite suppression.
Impacts
Our work is helping papaya growers understand when they can rely on biological control to suppress damaging populations of carmine spider mites. We have found that the predatory mite PHYTOSEIULUS MACROPILIS can generate strong spider mite suppression, even when the top predator (the web-building spider) is present.
Publications
- Steinkraus, D. C., G. O. Boys, and J. A. Rosenheim. 2002. Classical biological control of Aphis gossypii (Homoptera: Aphididae) with Neozygites fresenii (Entomophthorales: Neozygitaceae) in California cotton. Biological Control 25:297-304.
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Progress 01/01/01 to 12/31/01
Outputs
Our goal is to enhance the efficacy of biological pest control through an improved understanding of the basic ecology of parasitoids and predators. Work is being conducted in two agroecosystems. First, in California cotton we are exploring the ecology of generalist predators, and the ecological significance of predator-predator interactions. We have demonstrated that larval lacewings, CHRYSOPERLA PLORABUNDA, can exploit plant-produced food resources (extrafloral nectar) and survive extended periods when arthropod prey are absent. We have also shown that lacewing populations exhibit source-sink dynamics in cotton. Where herbivore prey are present at low to intermediate densities, higher-order predators exert strong predation on lacewings, producing local sinks. Where herbivores are present at outbreak densities, however, higher-order predation is relaxed and lacewing reproduction is therefore enhanced, producing source populations. Second, in Hawaii papaya, we are
exploring control of spider mites, TETRANYCHUS CINNABARINUS, by predatory mites, beetles, and spiders. We have shown that predator-predator interactions are important here as well, and that the nature of these interactions can be predicted from a knowledge of the foraging behavior of the component species. Spiders (sit-and-wait predators) can disrupt biological control that would otherwise be exerted by a high-mobility actively foraging predator, STETHORUS SIPHONULUS. Such disruptive effects are not, however, observed when PHYTOSEIULUS MACROPILIS, a lower-mobility, but still actively foraging predator, is present.
Impacts
Our results have helped California cotton growers better manage lacewing populations. In particular, we have shown that releases of commercially-produced lacewings is a misguided strategy, because of the negative impact of higher-order predators. In contrast, predatory mites are very effective for spider mite control in papaya, and are relatively insensitive to higher-order predation.
Publications
- Colfer, R. G., and J. A. Rosenheim. 2001. Predation on immature parasitoids and its influence of aphid population suppression. Oecologia 126:292-304.
- Limburg, D. D., and J. A. Rosenheim. 2001. Extrafloral nectar consumption and its influence on the survival and development of an omnivorous predator, larval Chrysoperla plorabunda. Environmental Entomology 30:595-604.
- Rosenheim, J. A. 2001. Source-sink dynamics for a generalist insect predator in a habitat with strong higher-order predation. Ecological Monographs 71:93-116.
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Progress 01/01/00 to 12/31/00
Outputs
The aim of this project is to enhance the efficacy of biological pest control through an improved understanding of the fundamental ecology of parasitoid-host and predator-prey interactions. Work is being undertaken in three agricultural ecosystems. First, in cotton, we have explored the role of several generalist predatory hemipteran bugs and the specialist predator GALENDROMUS OCCIDENTALIS as biological control agents of spider mites. We have found that the predatory mites are subject to predation by the hemipterans, preventing their establishment. Second, in papaya, we have shown that the predatory mite PHYTOSEIULUS MACROPILIS is an effective regulator of populations of the pest mite TETRANYCHUS CINNABARINUS, even when higher-order predators are present. Third, in grapes, we are exploring factors that limit the lifetime reproductive success of parasitoids in the genus ANAGRUS as biological control agents of leafhoppers in the genus ERYTHRONEURA. Longevity of ANAGRUS
females appears to be limited both by predation and by the lack of access to sugar-rich foods in the vineyard.
Impacts
Our results have shown that cotton growers can not rely on releases of GALENDROMUS OCCIDENTALIS for control of spider mites; this knowledge will reduce monetary losses in cotton, and enhance cotton productivity. We have also shown that papaya growers can use PHYTOSEIULUS MACROPILIS to control spider mites; this should reduce the use of acaricides significantly.
Publications
- Colfer, R. G., Rosenheim, J. A., and Godfrey, L. D. 2000. The evaluation of biological control of spider mites. Proceedings of the Beltwide Cotton Conference, Vol. 2:1151-1157.
- Godfrey, L. D., Rosenheim, J. A., and Goodell, P. B. 2000. Cotton aphid emergence as a pest of San Joaquin Valley cotton. California Agriculture (in press).
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Progress 01/01/99 to 12/31/99
Outputs
The aim of this project is to enhance the efficacy of biological pest control through an improved understanding of the fundamental ecology of parasitoid-host and predator-prey interactions. Work is being undertaken in three agricultural ecosystems. First, a key biological control agent of the grape leafhopper (a damaging pest of grapes) is the egg parasitoid ANAGRUS ERYTHRONEURAE, which requires an alternate host to overwinter. Providing alternate hosts (in a prune tree refuge adjacent to vineyards) yielded some early-season increases in leafhopper egg parasitism, but little change in overall pest densities. Second, one factor limiting the efficacy of the parasitoids APHYTIS AONIDIAE and COMPERIELLA BIFASCIATA as biological control agents of armored scales on almonds and citrus was discovered to be a previously unrecognized hyperparasite, ABLERUS CLISIOCAMPAE. Third, work in cotton showed that the omnivorous thrips, FRANKLINIELLA OCCIDENTALIS, is an important
biological control agent of spider mites (TETRANYCHUS spp.) during early-season cotton growth.
Impacts
Our results have shown that an omnivorous thrips that has previously been regarded as a potentially damaging pest is actually a beneficial arthropod. This should lead to a reduction in insecticide use in California cotton. In grapes, our results suggest that growers should not take land out of production by replacing grape vines with prune trees unless their vineyards are far from natural sources of overwintering ANAGRUS ERYTHRONEURAE.
Publications
- Murphy, B. C., J. A. Rosenheim, J. Granett, C. H. Pickett, and R. V. Dowell. 1998. Measuring the impact of a natural enemy refuge: the prune tree/vineyard example. Pages 297-309 in: C. H. Pickett and R. L. Bugg (eds), Enhancing Natural Control of Arthropod Pests Through Habitat Management. Wiley & Sons.
- Kattari, D., G. E. Heimpel, P. J. Ode, and J. A. Rosenheim. 1999. First records of hyperparasitism by ABLERUS CLISIOCAMPAE (Ashmead) (Hymenoptera: Aphelinidae). Proceedings of the Washington Entomological Society 101:640-644.
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Progress 01/01/98 to 12/31/98
Outputs
The goal of this project is to evaluate factors limiting the efficacy of biological control agents and to investigate means of enhancing the lifetime reproductive success of biological control agents by modifying the environment. Work in wine-grape vineyards suggested that planting a "refuge" of prune trees upwind of vineyards could provide a nearby overwintering site for a key parasitoid, ANAGRUS ERYTHRONEURAE, which attacks the eggs of the grape leafhopper. Refuges produced elevated levels of early-season parasitism. Suppression of overall leafhopper nymph and adult densities, was, however, minimal during the second and third generations (when economic damage occurs). Work in cotton suggested that large-scale releases of the western predatory mite, GALENDROMUS OCCIDENTALIS, are ineffective as a means of enhancing biological control of a complex of spider mites, TETRANYCHUS spp. Ongoing experimental work is attempting to determine the basis for this lack of efficacy,
and will include experimental tests of the role of plant-based factors and prey availability ("bottom-up effects") as well as the role of higher-order predators ("top-down effects"). The results of the ongoing work should reveal whether or not there are means of modifying the predator releases that will enhance their efficacy.
Impacts
(N/A)
Publications
- MURPHY, B.C., ROSENHEIM, J.A., DOWELL, R.V. AND GRANETT, J. 1998. Testing a habitat diversification tactic for improving biological control: parasitism of the western grape leafhopper, ERYTHRONEURA ELEGANTULA (Homoptera: Cicadellidae). Entomol. Exp. Appl. 87:225-235.
- COLFER, R.G., ROSENHEIM, J.A., GODFREY, L.D. AND HSU, C.L. 1998. Evaluation of predaceous mite releases for spider mite management. Pp. 976-982 IN Proc. Beltwide Cotton Conf., San Diego, CA.
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Progress 01/01/97 to 12/01/97
Outputs
The goal of this project is to evaluate factors limiting the efficacy of biological control agents and to investigate means of enhancing the lifetime reproductive success of biological control agents by modifying the environment. Work in almond orchards is focused on the importance of non-host foods (primarily floral nectar) and host-feeding in the ecology of APHYTIS AONIDIAE, the dominant parasitoid of San Jose scale, QUADRASPIDIOTUS PERNICIOSUS. There is a strong interaction in the effects of nectar and host-feeding: in the absence of nectar, host-feeding has minimal effects on longevity and fecundity, but in the presence of nectar, host-feeding has moderate effects on longevity and major effects on fecundity. Flowering cover crops are being evaluated experimentally. Work in upland cotton is focused on the importance of plant-linked factors and higher-order predators in the ability of populations of the predatory mite GALENDROMUS OCCIDENTALIS to establish, build,
and suppress populations of TETRANYCHUS spp. spider mites. In the presence of abundant spider mite prey, predatory mite populations often fail to establish in the field. Common hemipteran predators, including ORIUS TRISTICOLOR and GEOCORIS spp., prey heavily on predatory mites. The omnivorous thrips FRANKLINIELLA OCCIDENTALIS also consumes predatory mite eggs. When these predators are excluded, predatory mite populations appear able to grow if given adequate mite prey. Ongoing work will evaluate the importance of plant-based factors.
Impacts
(N/A)
Publications
- Heimpel, G.E., Rosenheim, J.A. and Kattari, D. 1997. Adult feeding and lifetime reproductive success in the parasitoid APHYTIS MELINUS. Entomologia Experimentalis et Applicata 83: 305-315.
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Progress 01/01/96 to 12/30/96
Outputs
The goal of this research is to implement novel approaches to biological controlof herbivorous insects in agroecosystems. First, we continue work on developing enhanced population regulation of the grape leafhopper in vineyards, capitalizing on the natural levels of egg parasitism provided by ANAGRUS EPOS. Second, work on biological control of early-season populations of the cotton aphid, APHIS GOSSYPII, has shown that natural levels of biological control agents (both coccinellid predators and the parasitoid LYSIPHLEBUS TESTACEIPES) are sufficient to provide consistent control of early-season populations that infest seedling cotton, which are present as transient populations in years where colonizing aphid populations are dense. Because the cotton plant can compensate completely for feeding damage generated by transient aphid populations, early-season aphids are non-pests. The plants compensate in part by enhancing the apical dominance of the plant, producing a more
reproductive growth form by suppressing the production of vegetative branches. Early-season aphids may be beneficial if they support the establishment of generalist predators that subsequently suppress other potentially important herbivores. Finally, we are documenting the community of generalist predators found on six dominant crops in the central valley of California: cotton, alfalfa, tomatoes, grapes, almonds, and walnuts.
Impacts
(N/A)
Publications
- Godfrey, L. and Rosenheim, J.A. 1996. Aphids and whiteflies in the San Joaquin Valley of California in 1995. Proceedings of the Beltwide Cotton Conference, pp.128-132.
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Progress 01/01/95 to 12/30/95
Outputs
Research was conducted on two systems to develop an understanding of ecological mechanisms underlying pest control by natural enemies and implications for the development of pest management systems. First, work was conducted on biological control of the cotton aphid, APHIS GOSSYPII, a key pest of cotton. Early-season aphids occur only sporadically and are effectively controlled by a complex of predators and parasitoids. Cotton can compensate fully for early-season aphid damage. A pathogenic fungus, NEOZYGITES FRESENII, was introduced from the southeastern U.S. in an attempt to supplement late-season mortality factors. Second, planting overwintering sites (prune trees) for ANAGRUS EPOS, an egg parasitoid of the western grape leafhopper, upwind of grape vineyards led to significantly enhanced early-season colonization of vineyards by parasitoids and enhanced parasitism of leafhopper eggs during the first generation. Mark-recapture studies with ANAGRUS using rubidium
labeling and fluorescent dusts showed that these parasitoids move from prunes to grapes in the spring and also colonize from other (external) overwintering sites. Prune trees also created a windbreak effect, enhancing colonization of vineyards by ANAGRUS. ANAGRUS move predominantly upwind once foraging within the grape canopy, and rapidly spread within a vineyard.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
Work focused on the influence of trophic interactions between biological controlagents on the overall efficacy of biological control in agroecosystems. A review of experimental and theoretical analyses of intraguild predation (IGP) was conducted. IGP occurs when two predators that share a common prey (and may therefore compete) also engage in predator-prey interactions with each other. IGP is common in communities of arthropod predators and parasitoids and in communities of natural enemies associated with soil-dwelling nematodes. IGP is less common among biocontrol agents of weeds and pathogens. Manipulative experiments are few, but demonstrate that IGP can disrupt control of pests, especially when IGP occurs between predators. In early-season cotton, IGP occurs when predatory coccinellid beetles consume aphids that have been mummified by parasitoids; overall control is, however, improved by adding the beetles. In mid- and late-season cotton, pest suppression is often
disrupted by the action of generalist hemipteran predators that prey heavily on lacewing larvae. The impact of one key predator, the assassin bug ZELUS RENARDII, changes as the predator develops. Earlier nymphal instars are less disruptive than later developmental stages, but still prey on lacewing larvae.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
I continue to focus on biological control of the cotton aphid, APHIS GOSSYPII inCalifornia's San Joaquin valley. The cotton aphid has recently emerged as a key pest of California cotton. We have found consistently excellent natural biological control of early-season cotton aphids by a parasitoid, LYSIPHLEBUS TESTACEIPES, and several predatory coccinellid beetles. Furthermore, cotton has a strong ability to compensate for early-season damage generated by transient aphid populations. Early-season aphids should not be viewed as pests. mid-and late-season aphids are, however, real pests, and natural biological control is only sporadically effective. We have developed quantitative thresholds for the densities of aphids that can be tolerated before cotton becomes sticky, and are currently developing presence/absence sampling techniques. Aphid outbreaks are primarily associated with the production of a large, dark morph of the cotton aphid, which is highly reproductive under
low-stress conditions in the field (e.g., mild temperatures); the small pale morph appears not be able to generate damaging populations. We have shown experimentally that the highly reproductive morph is produced by mild temperatures, short daylengths, and plants high in nutrients. Aphid populations can be induced to crash by: (1) high levels of plant water stress, (2) high temperatures, and (3) natural enemies (parasitoids, predators, and a fungal pathogen). Ongoing work aims to develop an understanding of when aphid outbreaks are likely to occur.
Impacts
(N/A)
Publications
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