Welcome to... THE SNYDER LAB RESEARCH PAGE     .

Currently, we have several ongoing projects in the lab:
 
 
 

1. Predator diversity and the biological control of aphids

Big-eyed bug eating a green peach aphid

The predator guild in Washington potato fields is dominated by predatory nabid and big-eyed bugs, and a taxonomically diverse group of spiders. We have found that predator densities vary between fields by several fold, depending on whether fields are managed organically or using conventional, broad-spectrum pesticides. One component of biodiversity – equitability – also varies dramatically between fields, but this difference is not clearly related to management regime. By experimentally manipulating predator equitability, we are examining how complexity at the top trophic level mediates the predators’ impact on aphids and other herbivores. By understanding the relationship between predator diversity and biocontrol in the potato system, we might better focus efforts to understand and perhaps eventually manipulate landscapes to improve in-field biological control. This project is funded by a USDA-NRI grant co-written by Cory Straub.

2. Conserving predators through habitat diversification

We have been examining the use of unplowed refuge strips to conserve predatory beetles and improve the biological control of root maggot (Delia spp.) flies on cole crops: radish, broccoli, cabbage, etc. These crops are an important component of production on smaller, diverse vegetable farms on the west side of Washington. The community of predatory beetles at our sites includes several species of smaller carabid and staphylinid beetles (< 1 cm in length) that eat root maggot eggs, and one common larger carabid beetle (> 1.5 cm), Pterostichus melanarius, that eats smaller beetles but not fly eggs. We conducted a series of field experiments designed to address two questions: 1) does intraguild predation by P. melanarius disrupt conservation biological control, and 2) would schemes to selectively conserve smaller beetles be effective at improving fly egg control? In two initial experiments we found that densities of smaller beetles were lower, and densities of fly eggs were higher, in the presence of P. melanarius. However, attempts to improve fly egg biocontrol by selectively increasing densities of small beetles in the absence of P. melanarius were not consistently effective, because the suppression of fly eggs broke down if alternative prey (aphids) were present. Overall, these results suggest that both intraguild predation and the presence of alternative prey can disrupt conservation biocontrol in this system. A web site describing this research is under construction; a draft is here. This project is funded by a USDA-WSARE grant co-written by Renee Prasad. Renee's work is featured here, along with some other sustainability work in the lab and elsewhere at WSU.

3. Alternative prey and biocontrol by generalist predators

One drawback of generalists as biocontrol agents is that they feed on prey other than the target pest, and so, in the short term, alternative prey might distract generalists from feeding on pests and thus weaken biocontrol. Conversely, the presence of alternative prey early in the season might allow predators to colonize fields before a target pest becomes abundant, and also supplement predator diets and increase predator reproduction. In these ways, over the long term, alternative prey can bolster predator densities and improve biocontrol. Thus, the time scale being considered might be important in determining whether alternative prey contribute to or detract from biocontrol. Our research focuses on the predators attacking aphids in potato fields in eastern Washington. The predator guild in these fields is dominated by the omnivorous predator Geocoris spp., which reliably makes up ca. 50% of the predator community. Geocoris feeds on both of the dominant insect pests, the Colorado potato beetle (“CPB”), Leptinotarsa decemlineata, and the green peach aphid (“GPA”), Myzus persicae. In short-duration field and laboratory experiments, we have found that the impact of Geocoris on CPB is disrupted when the GPA is abundant – Geocoris prefer to feed on aphids, and switch from eating CPB eggs. We will experimentally alter the densities of two types of alternative prey – GPA and detritivores – in a series of well-replicated field experiments, and measure the impact of these manipulations on CPB biocontrol. We will address two questions: 1) Do seasonal dynamics of alternative prey influence whether they contribute to or detract from overall biocontrol; and 2) Can we improve biocontrol by adding additional alternative prey to the system? Results of these field experiments will be used to test mathematical models of the potato system. This project is funded by our other USDA-NRI grant, co-written by Gary Chang.

4. Ecological links between soil fertility and insect biocontrol

Two important pests of potato spend a substantial portion of their life cycle underground – potato beetles pupate in the soil, while wireworms spend the entire juvenile stage underground – and so soil dwelling nematodes that attack insects (“entomopathogenic nematodes”) are ideally placed to attack these pests. The objective of our work is to examine several techniques to augment and establish populations of entomopathogenic nematodes in potato fields. Also, we will examine whether brassica cover cropping and green manures, which are already being used by many local potato growers to control plant feeding nematodes, will interfere with the establishment of entomopathogenic nematodes, or indeed whether cover cropping and entomopathogenic nematodes will work together to control beetle pests. We also will examine whether cover crops/green manures have a negative effect on predatory ground beetles and other soil-associated beneficials. We also plan to examine other advantages of cover cropping and green manures, including improvement of plant health by increasing soil health, and disease suppression. The goal is to provide growers with a more complete picture of the advantages and disadvantages to using entomopathogenic nematodes on their own and in combination with different cover crops and green manures. All of our research will be overseen and directed by the Organic Potato Grower Advisory Group (“OPGAP”), a group consisting of organic growers and processors assembled to support this project, but which we hope will serve as a clearinghouse for information on organic crop production more generally. This project is funded by a USDA-WSARE grant, with Ekaterina Riga in the Plant Pathology Department as the co-PI.

5. Replacement of native ladybird beetles by exotics

Animals face predation by a diverse community of natural enemies, which has led to the evolution of flexibility in behavior, morphology, or life history to allow animals to reduce their risk of being preyed upon. Aphid colonies represent a highly concentrated prey resource, and a guild of predatory arthropods is specialized to locate and rapidly exploit this resource. These aphid predators typically feed not only on the aphids, but also on one another, with this latter interaction known as intraguild predation (IGP). Exotic ladybird beetle species that have been introduced for biocontrol might circumvent the predator avoidance strategies of natives, because the natives might not recognize the new arrivals as an IGP threat. Indeed, establishment of exotic ladybird beetles has often been followed by declines in native ladybird species.

We have been investigating the population and community consequences of antipredator behaviors among a guild of native and introduced ladybird beetles that are now sympatric in pea fields in eastern Washington state. The community currently includes three coccinellid species that attack pea aphids: Hippodamia convergens and Coccinella transversoguttata, which are native, and a recently arrived exotic, C. septempunctata (“C7”). A second exotic species, Harmonia axyridis, is now expanding its range into eastern Washington. Following the arrival of C7, the native Coccinella species has nearly disappeared from agricultural fields, but the relative abundance of H. convergens has not changed. Thus, our community includes a mix of species with historic, new, and future sympatry, with one native species in decline but another withstanding invasion. We propose to measure predator recognition by each beetle species for the other, and look for correlations between predator recognition, successful predator avoidance, and persistence following invasion.This is a long-running side project, done on the cheap.

Contact
William E. Snyder
Department of Entomology
Washington State University
Pullman, WA  99164-6382
phone: 509/335-3724
fax: 509/335-1009
E-mail: wesnyder@wsu.edu