Effect of Chronic Exposure to Sublethal Doses of Imidacloprid and Nosema ceranae on Immunity, Gut Microbiota, and Survival of Africanized Honey Bees.

Large-scale honey bee colony losses reported around the world have been associated with intoxication with pesticides, as with the presence of pests and pathogens. Among pesticides, neonicotinoid insecticides are the biggest threat. Due to their extensive use, they can be found in all agricultural environments, including soil, water, and air, are persistent in the environment, and are highly toxic for honey bees. In addition, infection by different pests and pathogens can act synergistically, weakening bees. In this study, we investigated the effects of chronic exposure to sublethal doses of imidacloprid alone or combined with the microsporidia Nosema ceranae on the immune response, deformed wing virus infection (DWV), gut microbiota, and survival of Africanized honey bees. We found that imidacloprid affected the expression of some genes associated with immunity generating an altered physiological state, although it did not favor DWV or N. ceranae infection. The pesticide alone did not affect honey bee gut microbiota, as previously suggested, but when administered to N. ceranae infected bees, it generated significant changes. Finally, both stress factors caused high mortality rates. Those results illustrate the negative impact of imidacloprid alone or combined with N. ceranae on Africanized honey bees and are useful to understand colony losses in Latin America.

Impact of Chronic Exposure to Sublethal Doses of Glyphosate on Honey Bee Immunity, Gut Microbiota and Infection by Pathogens.

Glyphosate is the most used pesticide around the world. Although different studies have evidenced its negative effect on honey bees, including detrimental impacts on behavior, cognitive, sensory and developmental abilities, its use continues to grow. Recent studies have shown that it also alters the composition of the honey bee gut microbiota. In this study we explored the impact of chronic exposure to sublethal doses of glyphosate on the honey bee gut microbiota and its effects on the immune response, infection by Nosema ceranae and Deformed wing virus (DWV) and honey bee survival. Glyphosate combined with N. ceranae infection altered the structure and composition of the honey bee gut microbiota, for example by decreasing the relative abundance of the core members Snodgrassella alvi and Lactobacillus apis. Glyphosate increased the expression of some immune genes, possibly representing a physiological response to mitigate its negative effects. However, this response was not sufficient to maintain honey bee health, as glyphosate promoted the replication of DWV and decreased the expression of vitellogenin, which were accompanied by a reduced life span. Infection by N. ceranae also alters honey bee immunity although no synergistic effect with glyphosate was observed. These results corroborate previous findings suggesting deleterious effects of widespread use of glyphosate on honey bee health, and they contribute to elucidate the physiological mechanisms underlying a global decline of pollination services.