Bumble bees and apple trees: Experiment finds impact of neonicotinoid on pollination

A study in Nature reports the first evidence of a neonicotinoid pesticide directly impacting pollination by bees, according to the authors. In cage experiments, bumble bees exposed to a field-realistic dose of the neonicotinoid thiamethoxam made fewer visits to apple trees and collected less pollen compared to controls, reducing the number of seeds found in the resulting apples. The authors say their findings have ecological implications for pollination of both crops and wild plants.

 

Dr. Robbin Thorp, Distinguished Professor Emeritus, Department of Entomology and Nematology, University of California, Davis (webpage): 

Expertise: Bee biology, pollination ecology, foraging behavior and management of bee populations.

“This study produces evidence that sublethal doses of neonics are detrimental to the abilities of bumble bees to provide pollination services in apples.  Most previous studies have focused on direct effects of neonics on bee health, especially with honey bees. Neonic doses provided to bumble bee colonies in this study seem to be what would be expected under field conditions.

“Bumble bees are more effective pollinators of many crops, including apples, than honey bees are.  Bumble bees are especially effective on crops requiring buzz pollination (where flowers need to be vibrated to release pollen) such as tomatoes, eggplant, peppers, blueberries and cranberries, while honey bees are much less effective on these crops.  Greenhouse production of tomatoes globally has expanded dramatically over the past 25 years with our ability to produce and manage bumble bee colonies. Bumble bees are also much more important pollinators in native ecosystems than is the introduced honey bee.

“Extrapolation of the findings in this study to other crops and to other pollinators should be done with caution.  Floral morphology, especially pollen presentation and reception vary greatly among our crop species.  Bumble bees are social, large, hairy, strong flying bees, while the vast majority of the rest of our over 19,500 species of bees are solitary and vary widely in their physical characteristics and foraging abilities.

“The study is an important contribution to the ongoing study of the impacts of neonics, providing an element not fully explored in previous studies.  It provides clear evidence for effects on individual behavior of bumble bees and potential effects at colony level.”

 

Dr. Elina L. Niño, Assistant Specialist in Cooperative Extension – Apiculture, University of California, Davis (webpage):

Expertise: Honey bee biology, health, and reproduction; Chemical ecology and reproductive physiology; Pollination biology; Insect ecology; Evolution; Genomics.

“This study is interesting as it looks at not only how pesticide exposure affects bees but ultimately how it affects the final ‘product’ – the fruit. That is ultimately what bees do for us: provide pollination to ensure safety of the food supply. It shows the importance of focusing not only on the effects of neonicotinoids on bees, but also how their exposure can limit pollination success.

“The authors chose bumble bees because they are an important pollinator of apples but likely for a couple of other reasons. A recent study on the effects of seed coating of clothiandin (a neonicotinoid) didn’t find negative effects on honey bee colonies in a field setting, while it did find an effect on bumble bees and wild bees. Another reason, extrapolating from my own experience working with honey bees in a hoop house – bumble bees should be easier to track and they seem to do better in an enclosed space.

“Currently, we make many extrapolations based on toxicity data completed for honey bees and that is now proving not to be the smartest decision as we are seeing different impacts of pesticides on bees other than honey bees. It is great to see research being done on other pollinating bees as well, as there is clearly a need for it.

“One more thing to point out though is that a couple of results were borderline statistically significant while they were reported as significant. For example: ‘When whole colonies were given access to apple trees we found an effect of insecticide treatment on visitation rates to apple flowers (F2,86 = 3.1, P = 0.05); colonies exposed to 10 ppb pesticide provided lower visitation rates to apple flowers than controls (Fig. 1a; Extended Data Table 1).’ Normally P < 0.05 is considered significant.”

 

Dr. Gene Robinson, Swanlund Chair of Entomology & Director, Illinois Bee Research Facility, University of Illinois at Urbana-Champaign (webpage):

Expertise: Mechanisms and evolution of social behavior; sociogenomics; bee biology.

“Colonies of bumble bees treated with a neonicotinoid pesticide produce apples with reduced seed number, but individual bumble bees treated with the same dose do not.  This study highlights the complexities of life in the insect societies and illustrates why its important to perform pesticide research as the authors have done, at both the individual and colony levels. This is the only way we will truly understand the influence of pesticides on bees and the threat they pose to pollination services.”

 

Declared interests (see GENeS register of interests policy):

No interests declared.

 

Reference:

Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees‘ by Stanley et al, published in Nature on Wednesday 18 November, 2015.

Please feel free to leave your comments below, but be aware that by doing so you agree to our Terms & Conditions.