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Parasites, diseases and pesticides

Western honey bee populations face threats to their survival increasing interests into other pollinator species, like the common eastern bumblebee. North American and European populations were severely depleted by Varroa mite infestations during the early 1990s, and U.S. beekeepers were further affected by colony collapse disorder in 2006 and 2007. Some subspecies of Apis mellifera show naturally varroa sensitive hygiene, for example Apis mellifera lamarckii and Apis mellifera carnica. Improved cultural practices and chemical treatments against Varroa mites saved most commercial operations; new bee breeds are beginning to reduce beekeeper dependence on acaricides. Feral bee populations were greatly reduced during this period; they are slowly recovering, primarily in mild climates, due to natural selection for Varroa resistance and repopulation by resistant breeds. Although it is generally believed that insecticides have also depleted bee populations, particularly when used in excess of label directions, as bee pests and diseases (including American foulbrood and tracheal mites) are becoming resistant to medications, research in this regard has not been conclusive. A 2012 study of the effect of neonicotinoid -based insecticides showed "no effects observed in field studies at field-realistic dosages." A new study in 2020 found that neonicotinoid insecticides affected the developmental stability of honey bees, particularly haploid males were more susceptible to neonicotinoids than diploid females. The 2020 study also found that heterozygosity may play a key role in buffering insecticide exposure.