|European Honey Bee- Wikimedia|
The investigation by scientists at Purdue University began with reports of bee deaths during planting season in hives near the fields. Screening the bees for pesticides, they found neonicotinoid insecticide present in all the affected bees. Other bees in the hives were suffering from tremors and convulsions, typical effects of these pesticides.
Neonicotinoid insecticide is coated on all the corn seeds and about half of the soybean seeds planted in the vicinity. The compound remains in the soil for years, protecting the roots but also taken up by the plant. Small amounts in the pollen can be picked up by bees and other pollinators without immediate toxic effects.
Unfortunately the coated seeds are sticky so talc is added to them to keep the seeds flowing smoothly in the planters. The talc picks up the insecticide in concentrations up to 700,000 times the lethal dose for a bee. The light talc particles are easily spread by wind during planting and equipment cleaning, coating the plant surfaces visited by foraging bees who take it back to the hive.
The immediate answer would be to avoid the use of talc to reduce the lethal levels. The long term effects of low dose exposure from plants transporting it from the seed to flowers and pollen are currently unknown. In a world facing the need to increase food production to feed the growing population, we are likely to hear of more problems like this in the future.