Honey Bees and Other Pollinators – Vegetable Crops Hotline

Honey Bees and Other Pollinators

​As you all know, many of our vegetable crops are dependent upon pollinators to move pollen from flower to flower. The cucurbits, muskmelons, cucumbers, watermelons, pumpkins, and squash, are completely dependent on insect pollination. Eggplant, okra, lima beans, and peppers will set fruit without pollinators but can have increased yield if pollinators are present. Honey bees are likely the most important pollinators for most of these crops, but other pollinators such as a number of species of native bees and other insects can also provide useful pollination services. In recent years, there has been a lot of attention given to larger than normal die off of honey bee colonies, commonly referred to as colony collapse disorder. There has been a great deal of discussion in the scientific community and in the public about the cause or causes of these colony deaths. Some of the suspected causes include new disease organisms, Varroa mites feeding in the hives, and a relatively new class of insecticides, the neonicotinoids.

Many factors can determine the survival of honey bee colonies, particularly over the winter. According to our apiculturist, Greg Hunt, the average overwintering hive losses in Indiana have averaged about 30% over the last 10 years. After the severe winter of 2013-14, losses were about 65% statewide. This year, after a more normal winter, losses were about 29%. In addition to weather, Varroa mites and whether beekeepers treat for them can be important to hive survival. The impact of neonicotinoid use on bee health and hive survival is less clear.

The neonicotinoids have been on the market for about 20 years and have become one of the most popular groups of insecticides in the world. Their success has been the result of their low toxicity to humans and vertebrate wildlife, their effectiveness against both chewing and sucking insects, and their systemic activity, meaning they move through the plant and can kill insects at location throughout the plant. The neonicotinoid insecticides labelled for use on vegetable crops include Platinum®, Actara® and FarMore® seed treatment (thiamethoxam), Admire Pro® (imidacloprid), Assail® (acetamiprid), Belay® (clothianidin), Venom® and Scorpion® (dinotefuran) and Transform® (sulfoxaflor). There are also a number of pre-mixes that contain neonicotinoids. All of these are very toxic to honey bees, except for Assail®, which is only slightly toxic.

Recent work conducted by Christian Krupke and Greg Hunt in our department has shown that the dust created during planting of agronomic crops with seed treated with neonicotinoid insecticides has the potential for killing bees. Around planting time, they found lots of dead bees in hives near corn fields (which would be pretty much anywhere in Indiana) and found lethal concentrations of neonicotinoid insecticides in those bees and found it to be persistent in the soil. My group completed a study last year  (funded partially by the Indiana Vegetable Growers Association) that showed that neonicotinoid seed treatments, soil drenches, and foliar treatments on muskmelons resulted in levels of those insecticides in the pollen that could be lethal to bees, similar to recent research done elsewhere on pumpkins and squash.

Because of these concerns, the US EPA has charged each state with developing a pollinator protection plan, with a particular emphasis on potential pesticide effects. In Indiana, that responsibility has fallen to the Indiana Pesticide Review Board, on which I serve. Recently, we held an open forum that brought together beekeepers, farmers, pesticide applicators, Purdue scientists and educators, environmental groups, and others to establish a dialogue that will eventually result in a protection plan, with best management practices for all parties so that we can all achieve the common goal of continuing to produce our crops without harming honey bees and other pollinators.

As a vegetable grower, what can you do to protect bees? First, try to avoid spraying when crops are in bloom. This is obviously not always possible. For the cucurbit crops, flowers are only open for a single day, so if you spray insecticides in the evening after bees have gone back to the hive and flowers have closed up, you will reduce the impact on the pollinators. Second, when you have a choice, use the pesticide with the least effect on pollinators. See the Midwest Vegetable Production Guide (ID56) for recommendations. Relative toxicity levels to bees are shown in Table 10 on page 29. Finally, always use Integrated Pest Management (IPM), spraying insecticides only when necessary. Our research has consistently shown that spraying insecticides for striped cucumber beetle control based on the threshold of 1 beetle per plant (2-3 sprays) instead of weekly applications (8-10 sprays) not only resulted in fewer insecticide applications, but also led to significantly higher yields.

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