Wild Bees Decline Due to Pesticides and Food Scarcity
Research published by University of California, Davis scientists indicates that there is significant decline in wild pollinator populations due to food scarcity and pesticide exposure.
According to the lead author of the study, Clara Stuligross, a PhD candidate in ecology at UC Davis, it is very important that we understand how multiple stressors interplay. Wild bees are regularly exposed to both food scarcity and pesticides, especially for bee populations in agricultural systems, where many insects and pollinators are at risk due to industrial agricultural stressors. Just like humans, bees face multiple stressors.
Researchers designed a field study to explore and better understand the interplay between these two major stressors.
Two sets of mason bees were placed in cages to nest and stressors were separated. One set of bees had plentiful floral food availability the other set received sparse floral foods.
Within both food level groups, certain cages were treated with a Bayer Cropscience insecticide containing the neonicotinoid imidacloprid, called Admire Pro.
Significant impacts on the factors concerning mason bees’ reproductive success were identified by scientists, such as the likelihood that a female will nest, how many baby bees she will produce and the ratio of male to female offspring.
The findings were revealing. Female mason bees that were exposed to Admire Pro (imidacloprid) were 10% less likely to nest. When they did nest, they produced on average 42% less offspring. Those bees with limited food access produced 26% less offspring than those with plentiful food resources.
This unrelated 1:26-minute video by Pollinature shows some beautiful Osmia cornuta mason bees pollinating and living in specially built bee houses:
In comparison to the unexposed group, for those bees exposed to the two stressors there was an additive outcome, with limited floral resources and pesticide exposure combining to reduce reproduction by 57%.
The stressors also affected and changed the sex of successfully reared offspring. Exposure to the pesticide caused a 33% reduction in daughters, and resource limitation caused a 48% decline.
According to co-author Neal Williams, PhD, a pollination ecologist and professor in the Department of Entomology and Nematology at UC Davis, in the bee world limited male numbers don’t limit population growth, but fewer females can reduce reproductive potential for future generations.
Stressed mason bees slowed down their nest construction process by 32% from pesticide exposure and 20% due to limited food and these acted additively. They spent fewer days nesting, with bees exposed to pesticide starting to nest 3.5 days later than unexposed pollinators.
One particularly important discovery observed by scientists is that even though all the mason bees subjected to pesticide-treated flowers displayed negative responses to exposure only two of the eight pesticide-treated cages contained flowers with detectable levels of imidacloprid. This highlights a critically pernicious aspect of the pollinator crisis we face.
Manufacturers like Bayer are able to skirt responsibility and spin science to blame beekeepers or other factors rather than pesticide exposure for bee deaths due to the frequent inability of entomologists and beekeepers to trace pesticide-related bee deaths back to a source.
Although there is widespread crisis fatigue in the USA and around the world, our pollinator crisis is not abating, and pollinator populations are declining. Crop yields are limited due to US pollinator declines, in particular among native wild bees, as revealed in a study published earlier this summer.
Science shows that neonicotinoids are likely the most significant pesticide stressor to pollinators. Since habitat fragmentation and loss are unabating, we can't continue to subject critically important wild insects to these threats.
Data indicates that the planting of pollinator habitat by people with good intentions is not enough to curb the trend. In order for habitat to truly protect wild pollinators, it must be pesticide-free.
If you want to plant pesticide-free habitat for pollinators, or advocate for pollinator protection in your community, Beyond Pesticides has resources and information that can help you convince your local lawmakers to take some action.
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