Conservation biological control of alfalfa weevil in Wyoming

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Commodities

Practices

Alfalfa weevil is the most problematic pest for alfalfa hay producers in Wyoming. This introduced pest is most problematic in the early season causing defoliation and reducing hay yields and quality. Currently producers use insecticides or early cutting practices to control alfalfa weevil. Unfortunately these control methods can be costly or are not effective. Alfalfa weevil is not only a pest in Wyoming, but a pest of concern throughout the Western United States. Biological control of the weevil has been attempted through extensive releases of over 17 million parasitoid wasps of the alfalfa weevil by the USDA’s Agricultural Research Service (ARS) and Animal and Plant Health Inspection Service (APHIS) in the 1950s and again in the 1980s. These parasitoid populations still persist in Wyoming, but alfalfa weevil outbreaks continue to be variable and severe. Conservation biological control, managing habitats to promote already existing natural enemies, is a promising avenue for improving control of alfalfa weevil.

Parasitoids require nectar or aphid honeydew for adult survival. Providing wasps with these resources can increase their longevity and fecundity, allowing them to parasitize more hosts. Producers could accomplish provision of these resources through management of alternative habitats. Alternative habitats are non-cropped areas that can provide access to food for beneficial insects like parasitoids and pollinators through incorporation of floral resources. Besides nectar, these habitats may also provide refuge from disturbances and overwintering sites. However, we must better understand whether such habitats would enhance biological control enough to make an impact for producers and what the best way is to manage these alternative habitats.

The overall goal of this project is to determine if alternative habitats at the landscape and local scale have the ability to enhance biological control of alfalfa weevil. At the landscape scale, I will measure parasitism rates in producers' alfalfa fields across southeastern Wyoming and determine the effect of both in-field characteristics and those of the surrounding landscape. At the local scale, I will conduct a field study to compare visitation to annual and perennial flowering strips by parasitoids, other natural enemies, pests, and pollinators. This study is a pivotal first step in determining: a) which parasitoids are present in Wyoming and to what extent are they controlling alfalfa weevil and b) whether parasitoid populations are responding to alternative habitats at landscape or local scales. If parasitoids are responding positively to these alternative resources, there is the potential for growers to adopt habitat management practices to help control their pest problems. By reducing reliance on costly pesticides and risks of yield loss, producers can increase the profitability and long term sustainability of their operation, promoting biological control simultaneously with other goals such as conservation of pollinators, biodiversity, and water quality.

I will examine drivers of parasitism of alfalfa weevil by B. curculionis at a landscape and local scale. At the landscape scale I will focus on comparing parasitism rates between multiple field sites with different landscape characteristics and addressing these objectives:

Objective 1: Determine if landscape composition (percentage of crop and non-crop habitat) and landscape configuration (habitat continuity or isolation) affects parasitism rates in producer fields.

Objective 2: Evaluate whether flowering weeds and/or aphid populations in alfalfa fields could be providing parasitoids with in-field resources.

At the local scale I will focus on how parasitoids and natural enemies visit flowering alternative habitats.

Objective 3: Assess how abundance and community composition of arthropod functional groups (herbivores, predators, parasitoids, and pollinators) differ between different habitat types (annual flowers, perennial native flowers, alfalfa, control of fescue grass).