- Fruits: berries (strawberries)
- Crop Production: beekeeping, pollination, pollinator habitat, pollinator health
- Education and Training: extension, on-farm/ranch research
- Natural Resources/Environment: biodiversity
- Production Systems: organic agriculture
A diverse group of bee species, including both managed honeybees and wild native bees, are necessary to effectively pollinate commercially grown strawberries. Cultivated strawberries (Fragaria × ananassa Duch.) require pollination to produce marketable fruit, and strawberry seed set, fruit size, and fruit shape can be used to quantify pollination services. However, differences in pesticide application intensity may directly affect the pollination services provided by wild native bees.
Conventional strawberry growers routinely make over 20 synthetic pesticide applications annually to control pathogens, insects, and weeds during the season, most of which are preventative fungicide applications. Organic growers generally make fewer pesticides applications, typically less than 10 per growing season, and organically acceptable active ingredients may be less persistent in the enviroment. In order to measure the effects of pesticide exposure on native bees across a gradient of intensity, we will evaluate conventional and organic farms of both high and low pesticide intensity.
Higher pesticide intensity has been shown to reduce species abundance and richness, thereby reducing pollination services. Such reductions may reduce yield or increase the proportion of malformed berries, and may correlate with the gradient of pesticide intensity. Pesticides have been shown to reduce the pollination efficiency of bumble bees, but their effects on solitary bees are unclear. Further, greater pesticide intensity may reduce native bee immunity, increasing the likelihood of infection. We expected that farms with fewer pesticide applications, and organic farms which make fewer applications of less persistent insecticides, will support larger populations of native bees, which will in turn have greater immunity and result in measurably higher pollination services. This information will be used to both inform grower pest management recommendations to reduce impacts on pollinators and shared with policy makers to inform regulations aimed at improving pollinator health.
Project objectives from proposal:
Objective 1: Genotype microsatellites from key native bee species at southern strawberry farms, employing a range of pesticide use patterns, to estimate demographic parameters including effective population size.
Hypothesis 1: Fields with fewer pesticide applications will hold native bee populations with larger effective population size.
Objective 2: Evaluate pollinator efficiency by measuring berry seed set resulting from single bee visits.
Hypothesis 2: Fields with fewer pesticide applications will include more efficient individual foragers.
Objective 3: Evaluate native bee immunity by measuring phenoloxidase activity of field collected bees from conventional and organic sites.
Hypothesis 3: Fields with fewer pesticide applications will include individual bees with greater immune-competence.
Objective 4 (new): Identify potential strawberry pollinating species of flies and determine if these pollinators are impacted by above factors.
Hypothesis 3: Flies contribute a meaningful amount of pollination early in the strawberry fruiting period.