Wednesday, January 11, 2012

Pesticides Enter Bee Hives

Indiana experienced a massive honey bee die-off during 2010 resulting from poisoning by clothianidin, an insecticide highly toxic to honey bees, which is widely used on corn. Honey bees do not forage corn, a wind-pollinated grass, for nectar. However, they readily fly through corn tassels collecting poisoned pollen on their bodies when the plants have been treated with systemic insecticides. Clothianidin is in a class of insecticides called “neonicotinoids,” nicotine-based neurotoxins that are sprayed on foliage, sprayed on the soil, or coated onto seeds to kill gnawing or chewing insects that eat foliage or other plant parts. Systemic insecticides are carried throughout a plant and poison all plant parts, including nectar and pollen. Purdue University researchers studied the Indiana bee die-off to determine how neonicotinoids are transported from corn fields to honey bees and bee hives. The scientists identified several methods of insecticide contamination of bee hives near neonicotinoid-treated Indiana corn fields. Most corn is planted with seed coated with systemic insecticides. Talc is added to mechanical planters to prevent seeds from clumping. The scientists found clothianidin levels up to 700,000 times the lethal dose for honey bees in talc dust exhausted from planters. Also, significant levels of insecticide were found in the soil of corn fields as well as fields not currently planted in corn. Neonicotinoids are considered persistent; they remain toxic long after use. Outside the corn fields, dandelions, wildflowers attractive to honey bees, were also found to contain clothianidin.

Clothianidin was found in pollen stored in nearby bee hives. An exceptionally toxic effect occurs when honey bees gather clothianidin-contaminated corn pollen from fields treated with common fungicides, a widespread practice in North America. Dead bees found surrounding the hives contained clothianidin, either eaten by the bees or contacted with the bees’ bodies. The researchers caution that “sublethal doses of insecticides can weaken bees and increase susceptibility to key parasites or pathogens.” The study by Krupke et al. may be viewed at Today’s photo: clothianidin-treated broom corn.


  1. I would beg to disagree with one of your statements.

    "Honey bees do not forage corn, a wind-pollinated grass, for food."

    Maybe not on the corn in your area, or that you have pictured above, but I regularly see my bees foraging on corn anthers that pop out on the bottom side of the bowed tassels.

    This picture from Wikipedia is representative of the anthers I typically see my bees foraging:

    Maybe my girls are just more desperate for pollen in my area, in late summer...

    But you are also ultimately right about how much of it is in the air and the contact bees have with it there. Hives I've had pushed up against the edges of corn fields can sometimes have a very light film of corn pollen on the lids when I've arrived for inspections or to pull honey.

  2. Chuck,
    I agree with you. My wording was not quite accurate. Corn does not produce nectar, so honey bees don’t forage it for nectar. However, corn produces ample amounts of pollen—necessary to the corn plant since corn is wind-pollinated. Honey bees actively fly through corn tassels, covering their fuzzy bodies with pollen which they bring back to the hive.

    The picture that you linked to nicely illustrates the pollen-producing anthers on corn grown for food or ethanol production. My picture shows broom corn, an ornamental plant not grown in large plantings. It is the plant used in the production of brooms.

    Thank you for your attention to detail. I edited of this piece to help clarify the relationship between corn and honey bees.