Using prairies to reduce interacting stressors on pollinator health

Project

We are exploring how small patches of native, perennial vegetation (i.e., prairie) can increase the abundance and diversity of pollinators within corn and soybean. We observed honey bee colonies in Iowa lose weight beginning in August, when clover and soybean cease blooming. When colonies had access to a prairie from August to October, they were buffered from this late season decline. We are collaborating with the STRIPS project (Science-based Trails of Row-crops Integrated with Prairie Strips) to find farmer cooperators who allowed us to place a pair of sentinel honey bee hives within their prairie strips. We are investigating whether integrating small strips of prairie into commercial Iowa farms can increase the abundance and diversity of wild pollinators (including monarch butterflies) as well as improve honey bee forage. With funding from the Foundation for Food and Agriculture Research Foundation and multiple agribusiness partners, we have completed a full field season. We found farms where strips of reconstructed prairies were embedded in a crop field accounting for <10% of the area (referred to as prairie-strip sites) and farms (i.e., control sites) with no prairie within a 1.6 km radius and growing the same crop as the nearest prairie-strip site. We placed sentinel honey bee hives within the reconstructed prairies or the field margin of the control sites where the plant community was surveyed. Hive mass was weighed and pollen collected twice a month from June to September. Once per month (June to August), we used bee-bowls and timed observational surveys to assess pollinators and Monarch butterfly populations respectively. Flowering plants (including milkweed) were also counted along a 100m transect to measure potential forage. Prairie sites had more flowering species of plants (19 versus 7) and on average more flowers (31.75+19.6 vs 660.4+114) than control sites. Interestingly, control sites had more milkweed stems than prairie sites (28.2+5.13 in control vs 1.08+0.65 in prairie sites). However, we did not observe the same trend for adult monarchs, (3.33+0.85 in prairie sites vs 1.08+0.31 in control sites). Bees collected in the pan traps are being identified to species. Specific to honey bees, their colonies (i.e., hives) at prairie sites were significantly heavier than those at control sites. Significantly more pollen was collected from foragers at prairie than control sites. Honey bee populations did not differ between control and prairie sites, however, individual honey bees might be healthier at prairie-strip sties. We will test this assumption by measuring lipid content of adult honey bees.

What does it mean for farmers: Farmers and landowners interested in conserving pollinators have a viable option in reconstructing small patches of prairie. For more information visit the STRIPS website.

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