Crop pollination by honey bees contributes billions of dollars every year to the US economy. However, the bee keeping industry in the US is under stress. Introduction of mites that attack bees, bad weather, diseases and pesticides all have negative effects on honey bees. It is important to protect our honey bee pollinators.
However, we are often presented with conflicting goals by crop production. The goal of protecting pollinators often conflicts with the need to protect crops from insects that damage or destroy a crop. Both honey bees and the destructive insect pests are insects. It is not surprising that many of the methods (and pesticides) used to control destructive insects can also harm bees.
The policy goal of insecticide regulators is to balance the need for crop protection against the need to protect bees. Making the correct policy is tricky and requires re-evaluation of the policy as more experience and information are obtained. No policy is perfect.
Most recently, a conflict has embroiled the regulation of the insecticide spirotetramat. Spirotetramat is a new pesticide that is useful for controlling sucking insects such as whiteflies and aphids. Spirotetramat is a “systemic” insecticide, which means it is transported in the “sap” (vascular system) to all parts of the plant. Spirotetramat is effective because sucking insect drink the plant juices. Sucking insects don’t consume the outside of the plant, so surface insecticides can have less effect on sucking insects. Unfortunately, systemic insecticides are transported to the pollen and nectar of the plant. Bees feed on the nectar and use it to make honey. Bees collect pollen as food for the young bees (larvae). Thus, bees are exposed when they visit plants treated with systemic insecticides.
Bee keepers are concerned about insecticides (and especially systemic insecticides) because of the potential harm to their bees and their livelihood. To protect bees, most insecticides may not be applied to plants while in bloom and bees are visiting. This simple rule minimizes insecticide exposure and protects the bees. However, if plants are sprayed with a systemic insecticide before the plants bloom, the insecticide can appear in the nectar and pollen and bees will be exposed. Bee keepers dislike systemic insecticides because foraging bees are more likely to be exposed.
Efforts of spirotetramat opponents delayed registration by a couple of years based on technicalities. Late in 2010, however, spirotetramat was approved for use even though concerns remain. Spirotetramat at high doses is toxic to bee larvae. Insecticides can have negative impacts by altering bee behavior Testing has demonstrated that concentrations in plants are typically too low to cause noticeable effects on bees. It may be possible to use spirotetramat with minimal effect on bees, but its effect on bees needs to be closely monitored. As Murphy said, “What can go wrong, will go wrong.”
The registration of spirotetramat may not be a total loss for bee keepers. Compared other systemic insecticides such as the neonicotinoids, spirotetramat is much less toxic to bees. It only takes 0.039 ug of ingested imidicloprid to kill a honey bee. Clothianidin is even more toxic to bees than imidicloprid as previously discussed on this blog. It takes orders of magnitude more spirotetramat, 107.3 μg to kill a honey bee. If some uses of imidicloprid are replaced by spirotetramat, the overall effect could be less bee toxicity and less stress on the bee.
No method of pest control is perfect. There is always room for improvement. Entomologists never worry about running out of problems to solve. Because the public is concerned about our environment and willing to speak out, we have replaced many of the problematic pesticides with new ones with lower health, safety and environmental risks. Prior to the use of imidicloprid, pesticides that were highly toxic to people (such as parathion) were used to control whiteflies. Imidicloprid was a positive improvement for public safety. Spirotetramat may be an improvement in bee protection. We still need better control methods that are less hazardous to bees.