A controversy is brewing over the insecticide clothianidin and effects on honey bees. Some bee keepers have experienced large numbers of hive losses over the winter in recent years. The cause is unknown. Unknowns can lead desperate people to be convinced that a single plausible cause is indeed the problem, even if there is not a lot of evidence behind them.
What do we know? The insecticide clothianidin IS highly toxic to bees. Carbaryl (which is long been known to be highly toxic to bees) has a contact toxicity in the range of 1.3 to 33 ug/bee. Toxicity varies widely with formulation. Clothianidin is listed by EPA with a contact toxicity of about 0.04 ug/bee. By this standard, Clothianidin can be over 10 times as toxic to honey bees as carbaryl.
Clothianidin is used primarily as a seed treament. However, like most neonicotinoids, it can be translocated in the plant and into pollen and nectar. While seed treatments should minimize exposure to bees, products are not always used according to label and the translocation is problematic. Germany banned the use of clothianidin in 2008 for several reasons including bee toxicity.
However, the jury is still out on the relationship between colony collapse and Clothianidin or any other insecticide. Honey bee die offs have been reported for areas where Clothianidin is not in use. There are certainly a lot of other factors that may lead to honey bee loss. For example, our recent Indiana winters have had unusual warm periods. Warm weather causes honey bees to become active. If plant phenology is out of sync with the temperatures, then bees can have difficulty finding enough food. Without artificial feeding, colonies can starve.
Currently, there are a lot of media people who are convinced that pesticides are the culprit without solid evidence. These media storms can lead to wrong conclusions but take on a life of their own. When science does not have the answers, policy can sometimes come down to the most popular beliefs.