Study of the Effects of Sub-lethal Chronic Doses of Fungicide and Heavy Metal on Bee Health

Phytosanitary products are essential tools in agriculture to control pests and diseases, but they can pose a hidden threat to non-target organisms such as pollinators. These threats are exacerbated when the pollinators are exposed to more chemicals at the same time resulting in additive effects that impair different aspects of their lives. While insecticides have long been recognized for their impact on bee health and survival, fungicides were previously thought to be relatively harmless. However, recent research has shown that fungicides can also cause mild to severe damage to bees. The aim of the present research was to evaluate the effects of sublethal chronic intoxication with the fungicide boscalid and heavy metal copper (alone and in combination) on the social bees (Apis mellifera L.), and the solitary bees (Osmia bicornis L.). The experiments were carried out on bees in the laboratory and specific protocols were adapted for the bees to simulate natural conditions. The tests were carried out on newly emerged bees, but due to their social behavior, solitary bees were tested individually in cages, while honeybees were tested in groups. As the microbiome plays an important role in the survival of bees, and literature suggests that bees acquire the microbiome from their environment after emergence, the bees were conditioned for a few days to acquire the microbiome (pollen and gut homogenate for osmia bees and honeybees, respectively). After this preconditioning period, bees were subjected to treatments (boscalid, copper, boscalid + copper, and control) and fed with sublethal doses dispersed in a sugar solution. The daily syrup consumption rate for each bee was recorded, along with the evapotranspiration rates of control treatments. Longevity and mortality were also monitored. The correlation between body weight and head width of a sample of bees was calculated to estimate the average body weight of the entire group. Temperature and relative humidity data were recorded daily under controlled laboratory conditions. Bees were refrigerated at -80°C after 3, 5, and 7 days of microbiome acquisition for gut dissection and subsequent microbiome analysis.