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Posted 21 August 2010. PMN Crop News.

Pest Management Intensity Affects Wild Bee Populations, MSU Researchers Say

Source: Michigan State University Press Release.

East Lansing, Michigan (August 6, 2010)--Fruit and vegetable growers all over the country rely on pollinators, mainly bees, to stimulate high yields and abundant crops. In addition to managed honey bees, growers get pollination from wild bees that live in and around crop fields.


That’s what makes the work that Michigan State University entomologist Rufus Isaacs and entomology post-doctoral scientist Julianna Tuell are doing so critical.

The duo published an article in the June edition of theJournal of Economic Entomology that focuses on asking whether wild bee populations are affected by pest management programs employed by growers. This is an important question because fruit and vegetable producers need pollination from bees, but they also need to control insect pests and that may require application of insecticides.

During crop bloom, growers avoid insecticides, or they use only bee-safe products to ensure that pollinators are protected. After bloom, beekeepers can remove their honey bee colonies, but wild bees have nowhere to go. This can make crop fields more dangerous places for wild bees that live through the summer, such as bumble bees.

The article, “Community and Species-Specific Responses of Wild Bees to Insect Pest Control Programs Applied to a Pollinator-Dependent Crop,” looks into the relationship between insecticide applications to highbush blueberry fields and wild bee populations.

Wild bee conservation is regarded as essential for sustainable production of pollinator-dependent crops, yet little is known about the effects on wild bee communities of typical insect pest management programs used after bloom.“A rich wild bee community can be present before, during and after blueberry bloom with more than 100 species of wild bees found in these fields,” Tuell said. “Of these, approximately 10 species are present in high numbers and consistently pollinate blueberries.”

“Michigan is the leading producer of blueberries in the world, and this crop is very dependent on pollination for good yields,” Isaacs said. “It also faces some important insect pest challenges. This provides a great opportunity to test the hypothesis that insecticide applications made when the crop is not in bloom affect the wild bee community present during the bloom period – when bees are most important to the crops and to the growers.”

The pair developed an insecticide program risk index to quantify the relative risk to wild bees of insecticide programs applied to blueberry fields. The index was used to test whether there was a relationship between the insecticide program risk and the abundance, diversity and species richness of wild bee communities sampled.

Conducted over three growing seasons, the study was also able to gauge the temporal stability of the wild bee population.

In two of the three years of the study, bee abundance and species richness declined with increasing insecticide risk index values. Bee diversity declined with this risk index only in the first year.

“These results indicate that wild bee communities are negatively affected by increasingly intensive chemical pest management activities in crop fields,” Tuell said.

She said studying wild bee populations is important because it can help growers make informed decisions about their pest management program that will result in more sustainable crop pollination.

“Most insecticides are applied after the crop is finished blooming,” she said. “Growers who rent honey bee hives know to avoid spraying insecticides until after hives are removed. Many wild bees also provide pollination, however, they are more likely to come into contact with insecticides. Many native bees live in the ground and nest in crop fields or in field margins, and their nests are not able to be moved to a location that is safe from pesticide exposure.”

An important practical implication of this study is that growers can make choices about how to manage pests, with potential benefits for pollinators and the pollination services they provide during bloom.

“Growers can reduce the toxicity and amount of insecticides they apply for pest control, and they can make adjustments in the timing of application to crops,” Tuell said. “More focused spraying that only targets areas with pest infestation is also expected to improve the overall farm environment for bees. Our data suggests that reducing the risks of pest insect control programs to bees will help conserve populations of these beneficial pollinating insects that are active during crop bloom.”

“With fruits and vegetables an increasing component of the nation’s diet and honey bee colonies continuing to face challenges, it makes good sense to find strategies to help promote wild bees on farmland,” Isaacs added.

Isaacs’ work is supported by the Michigan Agricultural Experiment Station (MAES).

Eileen Gianiodis
517-432-1555, ext. 177