First, we need to mention that in general neonicotinoids are highly toxic to honey bees and native bees, and caution needs to be taken when using these insecticides. However, based on the information available so far, we advise growers not to blame bee colony declines and Colony Collapse Disorder (CCD) solely on neonicotinoids. Most researchers agree that the current bee situation is likely caused by a variety of stress factors, including pesticides (insecticides and fungicides), diseases (parasites and pathogens), malnutrition, migratory beekeeping, among others. Thus, it is likely that CCD is due to a combination of these factors.
Neonicotinoids are systemic insecticides, and thus the possibility exists to find residues in the pollen and nectar. These residues can reach lethal or sub-lethal concentrations under certain circumstances. Neonicotinoids can also persist in the soil for months or years after an application. However, this is strongly influenced by the rate and timing of application. Growers also need to be aware that not all neonicotinoids are equally toxic to bees. For instance, acetamiprid (Assail) is considered safer to non-target beneficials than other neonicotinoids. For blueberries, we recommend not to use neonicotinoid insecticides pre-bloom and never use them during bloom. Neonicotinoids are only recommended post-bloom, i.e., after removal of honey bees. For example, applications of the neonicotinoids thiamethoxam, imidacloprid and acetamiprid for aphid, grub, and leafhopper control can be made only post-bloom.
Recent research and popular press articles have pointed out links between the use of ergosterol inhibiting fungicides (SI’s) and their ability to synergize the toxic effects of some neonicotinoids on bee toxicity. SI fungicides registered for blueberries include Indar, Orbit, and Quash. The toxic effects on bees varies with the neonicotinoids being used, and not all neonicotinoids have been shown to be equally synergized with SI fungicides. Some work has shown that while acetamiprid may be safer to bees than some other neonicotinoids, when used with some SI fungicides, its toxicity is greatly magnified. Therefore if bees are present in a field, it is much safer to stay away from any SI fungicide and neonicotinoid use.