The EEB & Flow: pesticides

*Guest post by Sonya Sharma, a student in Marc's 'Causes and Consequences of Diversity' class.

A rusty patched bumblebee (Getty Images)

Behind the scenes of the food we see stocked in grocery stores are arguably one of the most important organisms in the world, bumblebees (Bombus), which provide pollination in both natural and managed systems. However, human food security may be at risk because of the recent worldwide declines in bumblebee populations.

Land-use change is generally accepted as being the main driver of bumblebee abundance decline. Numerous studies have documented reductions in bumblebee populations more noticeably in areas that have gone through anthropogenic changes, such as agricultural intensification and urbanization. Bumblebee species richness seems to be positively correlated with the availability of grassland resources, such as pollen sources and nesting habitat, which are scarce in agricultural landscapes. Additionally, due to the mechanical disturbances across large areas that are characteristic of agricultural landscapes, they do not typically provide suitable habitat for wild bumblebee populations. Furthermore, bumblebees have a limited flight range, long colony cycle and specific food and nesting requirements that cause them to be especially susceptible to habitat loss.

Another factor that could be leading to the wild bumblebee decline is pathogen spillover from commercialized or domestic bumblebee populations. The commercialization of bumblebees as agricultural pollinators has inadvertently made wild populations more susceptible to a variety of emergent diseases and epidemics. Commercial rearing facilities provide an ideal environment for the development of a high load of pathogens and parasites because of the high density and high rates of transmission in these facilities. Constant pathogen spillover from commercialized bumble bees with high parasite loads could potentially extirpate small wild bumblebee populations.

A bumblebee hive- similar to ones placed in agricultural landscapes (Wikipedia)

A further contributing factor to the decline in bumblebees is the use of pesticides. Specifically, neonicotinoid containing pesticides, which are most widely used globally, have been found to dramatically reduce egg-laying by queen bumblebees. To mitigate neonicotinoids detrimental effects, a new class of pesticides are being adopted worldwide, sulfoximines. However, a recent study suggests that sulfoximines may also diminish queen bumblebees’ reproductive capacity. Exposure to small amounts to a sulfoximine containing pesticide caused colonies to produce 54% fewer male drones and no new queen bees (Meeus et al., 2011). Therefore, pesticide use is very likely a contributing factor to the widespread bumblebee decline.

All factors considered; we can conclude that bumble bee populations are in serious risk of losing diversity and possibly going extinct. However, when it was proposed in June 2018 to include four species of bumblebee in the Californian Endangered Species Act, the state was sued by the Californian Farm Bureau Federation and six other agricultural associations. These groups argue that bees cannot be protected under this law because it defines candidate species as “bird, mammal, fish, amphibian, reptile or plant” and does not list any insects.

This conflict in government policy is not unique to California however, and is an example of the longstanding tension between conservation biologists and the agricultural industry about the protection of pollinators. If bumblebees were listed on the Californian Endangered Species Act it would restrict grazing, pesticides and the use of commercial bumblebees. It could also limit where bumblebee hives could be placed. Farmers and ranchers claim that listing bumble bees would harm agricultural production dramatically.

Other environmentalists suggest that attempts to conserve bumblebees should focus more on wildlife-friendly approaches such as increasing agricultural land set-asides, hedgerows and employing integrated pest management. Whatever the strategy taken through policy to protect bumblebees, it should aim to increase the abundance of grassland resources, reduce pathogen spillover from commercialized populations and reduce the use of harmful pesticides. How to create a policy that will appease both the agricultural industry and conservation biologists is still up for debate. However, all can agree that bumblebees are an indispensable member of both managed and natural ecosystems.

Works Cited:

Grixti, J. C., Wong, L. T., Cameron, S. A., & Favret, C. (2009). Decline of bumble bees (Bombus) in the North American Midwest. Biological Conservation, 142(1), 75–84.

Meeus, I., Brown, M. J. F., Graaf, D. C. D., & Smagghe, G. (2011). Effects of Invasive Parasites on Bumble Bee Declines. Conservation Biology, 25(4), 662–671.

Tuesday, March 24, 2020

The Fight for Bumblebees