Andrew set out to test bees’ response to various diets and levels of pesticide exposure. Knowing that higher parasite loads are an indicator of poor health2, he used the honey bee gut endo-parasite Nosema ceranae (Figure 1) as a proxy for bee health. Using pollen trapped from four crops (black cap raspberry, meadow foam, crimson clover, almond; Figure 2), Andrew set out to test differences in pesticide exposure in different crops, as well as stress caused by pesticide-laden pollen. He also wondered whether a more diverse diet could better combat that stress. Feeding bees various combinations of different types of pollen with differing levels of pesticides, Andrew found some unexpected things.
In the summer of 2012, BIP heard from a North Dakota beekeeper who mentioned that bees used to pollinate sunflower crops (Figure 3) had a particularly bad year. North Dakota was in the middle of a severe drought that year, and the beekeeper thought this may have had an effect on the sunflowers and thus maybe the bees. Andrew sprang into action. He thought there may be some connection to pollen nutrition and pesticide exposure.
He found that sunflowers grown under drought conditions were smaller in size, affirming that they were in fact stressed by the lack of water! Furthermore, the pesticide load in pollen collected from treated plants was higher in drought stressed plants than in well-watered plants. This showed that drought does affect the way the plants take up systemic pesticides. Does this have an effect on the bees foraging on them? The answer is probably. Bees infected with Nosema died faster than uninfected bees who were fed the same diets of severely drought stressed pollen. This was true regardless of whether the pollen came from flowers grown using treated or untreated seeds! With regards to the moderately drought stressed pollen, infected bees died faster than their uninfected counterparts only when the moderately drought stressed pollen came from seed-treated plants. This finding points to both drought and pesticide exposure having
1. Morse, R. A., & Calderone, N. W. (2000). The value of honey bees as pollinators of US crops in 2000. Bee Culture, 128(3), 1-15.
2. Pettis, J. S., Lichtenberg, E. M., Andree, M., Stitzinger, J., & Rose, R. (2013). Crop pollination exposes honey bees to pesticides which alters their susceptibility to the gut pathogen Nosema ceranae. PloS one, 8(7), e70182.
3. vanEngelsdorp, D., Underwood, R., Caron, D., & Hayes Jr, J. (2007). Estimate of managed colony losses in the winter of 2006-2007: A report commissioned by the Apiary Inspectors of America. American Bee Journal, 147(7), 599-603.
4. Di Pasquale, G., Salignon, M., Le Conte, Y., Belzunces, L. P., Decourtye, A., Kretzschmar, A., ... & Alaux, C. (2013). Influence of pollen nutrition on honey bee health: do pollen quality and diversity matter? PloS one, 8(8), e72016.
About the Author:
Kelly Kulhanek is a PhD student in the vanEngelsdorp bee lab. She is studying the effect of beekeeper management practices on honey bee colony health and survival.