Insecticides Can Affect Wild Bee Populations, MABR Research Shows

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Fruit and vegetable growers all over the country rely on pollinators—mainly bees—to produce crops from blueberries to almonds. In addition to managed honey bees, wild bees that live in and around crop fields also provide pollination services.

To help growers make pest control choices that conserve these valuable native pollinators, MABR entomologist Rufus Isaacs and entomology postdoctoral scientist Julianna Tuell studied how wild bee populations are affected by pest management programs in highbush blueberries. The research is published in the June issue of the Journal of Economic Entomology.

During crop bloom, growers avoid using insecticides or use only bee-safe products to ensure that pollinators are protected. After bloom, honey bee colonies are removed from the fields, but wild bees stay in the fields.

“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 added. “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.”

Tuell and Isaacs developed a risk index to quantify the relative risk to wild bees from insecticide applications to blueberry fields and then analyzed the relationship between the index and the abundance, diversity and species richness of wild bee communities over three growing seasons. The study also evaluated the stability of the wild bee population.

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

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

She said that 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 native bees live in the ground and nest in crop fields or in field margins, where they are likely to come into contact with postbloom insecticides.”

Using the scientists’ results, growers can make more informed choices about how to manage pests while continuing to get benefits from wild bees.

“Growers can reduce the toxicity and amount of insecticide they apply for pest control, and they can make adjustments in application timing,” Tuell said. “More focused spraying that targets only pest-infested areas also is expected to improve the overall farm environment for bees. Our data suggest that reducing the risk of pest 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 said.

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