Bees are dropping like flies

Nieuws | de redactie
22 augustus 2013 | The number of honey bees is plummeting around the globe. New research shows that the most important pollinator is not just killed by insecticides. Pesticides increase the susceptibility to a variety of other deadly pathogens, like Nosema spp.

Honey bees are one of the most important pollinators of agricultural crops. Recently their number has strongly declined which caused great concern around the globe, since more and more important crops require insects for pollination. Pesticides, habitat destruction and climate change all had a big negative impact on honey bees.

Recent research suggests that honey bee diets, parasites, diseases and pesticides interact to have stronger negative effects on managed honey bee colonies. Lack of food and non-lethal doses of pesticides in particular make bees more prone to deadly diseases and parasites, conclude Pettis et al. on their research paper on PlosOne.

Gazillion sub-lethal effects

Recent research is uncovering diverse sub-lethal effects of pesticides on bees. Insecticides and fungicides can alter insect enzyme activity, their development, offspring sex ratios, mobility, navigation and immune function. Such findings are of great concern given the large numbers and high levels of pesticides found in honey bee colonies. Thus it is crucial to determine how field-relevant combinations and loads of pesticides affect bee health.

Reduced immune functioning is of particular interest because of recent disease-related declines of honey bees. Pesticide increases susceptibility to potential lethal diseases including the gut parasite. These increases may be linked to insecticide-induced alterations to immune system pathways, which have been found for several insects, including honey bees.

Affected individual and colony functioning

Studies of colony food reserves and bee wax have found high levels and diversity of chemicals in managed colonies. These mixtures have strong potential to affect individual and colony immune functioning. One pathogen of major concern to beekeepers is Nosema spp which severely affects honey bee colony health, and can result in complete colony collapse. Infection with Nosema in the autumn leads to poor overwintering and performance the following spring, and queens can be superseded soon after becoming infected with Nosema.

“We detected 35 different pesticides in the sampled pollen, and found high fungicide loads. The insecticides esfenvalerate and phosmet were at a concentration higher than their median lethal dose in at least one pollen sample. While fungicides are typically seen as fairly safe for honey bees, we found an increased probability of Nosema infection in bees that consumed pollen with a higher fungicide load”, the researchers conclude.

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