Summer is in full swing. Soybeans are beginning to bloom, corn is tasseling and sunflowers will start to show their flashy yellow flowers soon. Include the vast fields of alfalfa with the aforementioned crops and it’s clear there are many acres of flowering crops that are extremely attractive to pollinators. 

Many farmers have asked about the impact of insecticides on pollinators. Here is what we know about pollinators and insecticide exposure and important steps to take to mitigate their harmful effects on these important insects. 

Before we go into the details of research that’s been done on this issue, let’s briefly introduce the insects. “Pollinator” is a broad name given to any insect that moves pollen from the male to the female parts of a flower or between flowers. The staple pollinators that many of us picture in our heads when we think of pollinators are probably bumble bees and honey bees. Honey bees are especially well adapted to pollination and have been used extensively in commercial operations to pollinate crops. These commercial hives have been at the epicenter of Colony Collapse Disorder (CCD) and the mysterious disappearance of the honey bees. 

However, there are many other pollinators. Many of them are smaller bees commonly referred to as ‘sweat bees’ (Photo 1). These native bees are equally important components of the pollinator community. Many pollinators visit not only the flowering crops, but they also frequent and collect pollen from all flowering plants around the fields. You can find more information on bees as pollinators in a blog post by Hannah Hamilton, a USGS scientist.

Figure 1. (Above) Sweat bee.
Photo by: Ada Szczepaniec

Pollinators have received much media attention in the last 10 years or so, and most of it centers on CCD and its causes. 

Commercial honey bees are exposed to many stressors, such as varroa mites, viruses, frequent shipment, extreme changes in environmental conditions, and insecticide residues. Recent research suggests that a combination of these factors is to blame for the decline in honey bee health. The article Declining Bee Populations Pose A Threat to Global Agriculture summarizes the different perspectives on this issue. 

Insecticides implicated in declining honey bee health in particular are the neonicotinoids. Last year, we wrote about the EPA label changes to prevent bee exposure to neonicotinoid insecticides. This seems to be obvious, but what is less obvious is the fact that neonicotinoid seed treatments may also be harmful to bees. In an extensive research project published in 2012, Christian Krupke from Purdue University and his collaborators describe that dead and dying bees collected from an apiary during corn planting in Indiana tested positive for clothianidin, a neonicotinoid insecticide used in Poncho seed treatments for corn. 

The insecticide residues were also detected in soil samples from fields not planted with neonicotinoid seed-treated crops for two previous years. Dandelions collected from edges of the fields, and in talc that was used as an additive for planting the neonicotinoid-treated seed. Authors speculate that this tainted talc expelled by planters may be coming in contact with the bees or may be deposited on plants that the bees visit. 

What can we do to minimize exposure of bees to insecticides and promote their health? The South Dakota Department of Agriculture outlines steps that can be taken to mitigate toxic effects of insecticides applied to field crops that may affect pollinators. Also, in a joint article the Iowa State University and Purdue University entomologists summarize the research paper mentioned above and offer additional recommendations. 

It’s important to note that this is a very hot research topic right now and much research is still needed to fully uncover the causes and mechanisms of declining bee health. For now, we need to take necessary actions to minimize exposure of pollinators to insecticides and be aware that insecticides have the potential to harm bees if they come into direct contact with them.