Small Striped Bee (Halictus). Photo USGS Bee Inventory.
Diverse and abundant native bee populations are found in areas where there are many patches of natural habitat. Specifically, studies indicate fields 1,000 to 6,000 yards from the nearest natural patch will have the most pollination from native bees [8, 9].
Pollinator habitat should have a diversity of flowers that bloom at different times to sustain a diverse group of pollinators throughout the growing season. Flowering plants in your hedgerows, riparian buffers, set-aside areas and gardens can all provide essential food. Not all flowering plants are equal! Some species provide lots of nectar, others provide lots of pollen, and pollen nutrients of different plants vary. It is important to encourage the growth of a wide variety of flowering plant species to best feed your bees, especially generalists like bumble bees. For specialists, like the squash bee, the specific host (squash or pumpkin) must be in the landscape.
Nearly 70 percent of bee species nest underground. Most other bees choose to nest in wood tunnels, occupying existing holes in snags or chewing into the pithy center of stems . Because many ground dwelling bees only range a few hundred yards from their nest, it can be even more important for land managers to provide nesting habitats directly on the farm. Bumble bees often prefer undisturbed areas such as hay fields and pasture . Many bees prefer to nest in sunny, bare patches of soil . When you excavate a pond or ditch leave the piles of excavated earth. Ground dwelling bees may nest in bare areas of mounded earth. Consider keeping some dead snags. Some solitary bees nest in abandoned beetle tunnels in snags.
Include flowering plants in your cover crop mixtures and give them time to flower to provide additional bee forage. Penn State's Dr Shelby Fleischer is working on building summer and fall cover crop mixtures that flower successively providing continuous forage for bumble bees and honey bees. The current summer mix trial includes buckwheat, mustard, sunflower, sunhemp and cowpea. The fall planted mix includes peas, vetch, clover and an oat nurse crop. We are still learning about cover crops for bee forage.
Many native bees nest in the ground. Sometimes they nest right in the area where the crop is grown and other times in attractive areas in field edges. Think about ways to avoid disrupting this nesting habitat in some areas of the farmscape. For example in one study farms that practiced no-till had triple the rate of squash bee visitation rates . In other studies farms with pastures or hayfields had more bumble bees.
During times of drought, irrigation may also encourage native bee pollinators. In one of two years (a dry year) of a study of pumpkin pollinators in Virginia, fields with irrigation had significantly more squash bees than those that did not . Researchers don't know why irrigation might increase ground dwelling native bees, but they speculate it might be differences in soil temperature or ease of making a nest.
8. Kremen, C., N.M. Williams, and R.W. Thorp, Crop pollination from native bees at risk from agricultural intensification. Proceedings of the National Academy of Sciences of the United States of America, 2002. 99(26): p. 16812-16816.
9. Klein, A.M., I. Steffan-Dewenter, and T. Tscharntke, Pollination of Coffea canephora in relation to local and regional agroforestry management. Journal of Applied Ecology, 2003. 40(5): p. 837-845.
10. Web Soil Survey.
11. Svensson, B., J. Lagerlof, and B.G. Svensson, Habitat preferences of nest-seeking bumble bees (Hymenoptera : Apidae) in an agricultural landscape. Agriculture Ecosystems & Environment, 2000. 77(3): p. 247-255.
12. Linsley, E.G., The ecology of solitary bees. Hilgardia, 1958. 27(19): p. 543-599.
13. Shuler, R.E., T.H. Roulston, and G.E. Farris, Farming practices influence wild pollinator populations on squash and pumpkin. Journal of Economic Entomology, 2005. 98(3): p. 790-795.
14. Julier, H.E. and T.A.H. Roulston, Wild Bee Abundance and Pollination Service in Cultivated Pumpkins: Farm Management, Nesting Behavior and Landscape Effects. Journal of Economic Entomology, 2009. 102(2): p. 563-573.
This article is part of a five part series describing pollinators, pollinator threats and on-farm conservation strategies as part of a collaboration between Penn State's Center for Pollinator Research and Penn State Extension Vegetable and Small Fruit Team.