Honey bees are an important part of modern agriculture. Most of our food crops require insect pollination and honey bees are often the #1 pollinator.
In the past decade, honey bees have been under increasing stress from parasites such as tracheal mites and Varroa mites, phorid flies, pesticides and other factors. Last year, I posted some of the concerns about the effects on bees of the insecticide, clothianidin and the EPA memo that was
brought to light widely distributed by Wikileaks. Germany and other European countries have already banned clothianidin because of problems with bee kills over the protestations of the manufacturer.
Clothianidin is commonly used as a seed treatment on corn. In a seed treatment, the corn seed is coated with a mixture that “coats the seed with the clothianidin. Clothianidin is systemic, meaning it is taken into the corn plants through the roots and translocated throughout where it can protect the corn plants against corn rootworm and other harmful insects. Ideally, the clothianidin goes into the soil, is covered by the planter and is unavailable to kill bees and other non-target species.
A new article published in the journal, PLoS One by a team of scientists (including some colleagues at Purdue), shatters the belief that clothianidin is not having an impact on bees. Their research documents the presence of clothianidin in bee hives and documents several plausible routes of movement from treated seed to honey bees.
One transfer mechanism is talc. Seed treatments can cause seeds to clump and thus beplanted at incorrect spacing. Sticky seeds cause mechanical planters to plant two seeds in the same place. Bad seed placement interferes with plant growth and reduces yield. To prevent clumping, farmers often add talc (the type that is used in “baby powder”) to the seed. The talc solves the seed clumping problem, but talc is a fine powder that is easily blown by the wind. Some of the seed coating and clothianidin become attached to the talc particles and are blown off site. The talc can coat dandelions and other flowers near the edges of fields that are visited by bees. The talc sticks to the pollen, and bees carry the pollen back to the hive to make food for their brood. In addition, some of the talc remains in the planter after planting. Common cleaning practice is to blow the talc out of the planter, a process that sends clouds of talc into the air.
Bees potentially encounter the highest concentrations of clothianidin by feeding on the talc that lands on flowers and is mixed with their pollen. The bees are literally “eating our dust”. A more indirect transfer is for the clothianidin from the talc to wash into the soil, be taken up by the plants (such as dandelions) and incorporated into the pollen of the plants. Bees foraging on dandelion pollen can receive unanticipated exposure.
A second mechanism of clothianidin transfer to bees is incorporation into the pollen of the corn plants. Clothianidin taken up by the plant roots is transported to all parts of the plant including the pollen. Corn produces a lot of pollen. Bees located near corn fields have a convenient source of pollen nearby. The pollen transported to the hive from treated fields contains clothianidin.
Clothianidin is a neurotoxin that is orders of magnitude more toxic to insects than to humans. It has replaced some of the organophosphorous insecticides that are implicated in human pesticide poisonings. In terms of human safety, clothianidin is far safer to use. However, clothianidin is one of the most toxic pesticides known to bees. Bees can potentially get a lethal dose of clothianidin from talc during the planting. In fact, bee kills near corn fields that were recently planted was the impetus for the PLoS One Study.
Direct kills of bees are not the only worry with neurotoxic insecticides. Bees are social animals that rely on complex behaviors and social interactions to maintain viable colonies. Thus, bee keepers must worry about sublethal levels of neurotoxins that alter bee behavior and make the bees unable to maintain their colony structure.There are clear problems with the use of clothianidin seed treatments that need further review and consideration. Perhaps it is possible to change the seed treatment formulation to avoid poisoning bees with clothianidin laden talc? The clothianidin in the pollen may be a more difficult issue to address, but perhaps alterations in formula or concentration could reduce the negative effects?
With any method of pest management, there is no silver bullet, no one solution that will manage the insects yet have no negative side effects. There is always room for improvement. It will be interesting to follow the developments over the next year as the manufacturers, bee keepers, EPA, farmers and scientists try to sort out the best way forward.