[Pollinator] effect of parasites, pesticides, etc. on bumble bees

[David Inouye]

Botías, C., et al. (2021). "Multiple stressors interact to impair the 
performance of bumblebee Bombus terrestris colonies." Journal of Animal 
Ecology 90(2): 415-431.
     Bumblebees are constantly exposed to a wide range of biotic and 
abiotic stresses which they must defend themselves against to survive. 
Pathogens and pesticides represent important stressors that influence 
bumblebee health, both when acting alone or in combination. To better 
understand bumblebee health, we need to investigate how these factors 
interact, yet experimental studies to date generally focus on only one 
or two stressors. The aim of this study is to evaluate how combined 
effects of four important stressors (the gut parasite Nosema ceranae, 
the neonicotinoid insecticide thiamethoxam, the pyrethroid insecticide 
cypermethrin and the EBI fungicide tebuconazole) interact to affect 
bumblebees at the individual and colony levels. We established seven 
treatment groups of colonies that we pulse exposed to different 
combinations of these stressors for 2 weeks under laboratory conditions. 
Colonies were subsequently placed in the field for 7 weeks to evaluate 
the effect of treatments on the prevalence of N. ceranae in inoculated 
bumblebees, expression levels of immunity and detoxification-related 
genes, food collection, weight gain, worker and male numbers, and 
production of worker brood and reproductives. Exposure to pesticide 
mixtures reduced food collection by bumblebees. All immunity-related 
genes were upregulated in the bumblebees inoculated with N. ceranae when 
they had not been exposed to pesticide mixtures, and bumblebees exposed 
to the fungicide and the pyrethroid were less likely to have N. ceranae. 
Combined exposure to the three-pesticide mixture and N. ceranae reduced 
bumblebee colony growth, and all treatments had detrimental effects on 
brood production. The groups exposed to the neonicotinoid insecticide 
produced 40%–76% fewer queens than control colonies. Our findings show 
that exposure to combinations of stressors that bumblebees frequently 
come into contact with have detrimental effects on colony health and 
performance and could therefore have an impact at the population level. 
These results also have significant implications for current practices 
and policies for pesticide risk assessment and use as the combinations 
tested here are frequently applied simultaneously in the field. 
Understanding the interactions between different stressors will be 
crucial for improving our ability to manage bee populations and for 
ensuring pollination services into the future.


-- 
Dr. David W. Inouye
Professor Emeritus
Department of Biology
University of Maryland

Principal Investigator
Rocky Mountain Biological Laboratory