A new study from Rutgers University establishes the link between lack of pollinators, such as bees, to reduced US crop yields for apples, cherries, blueberries, and more.
The most comprehensive study of its kind to date, the nationwide research inquired the extent to which pollinator limitation affects crop yield. The Rutgers-led research team covered seven crops across 131 locations in the country's major crop-producing areas.
Five of the seven crops in the study were found to have suffered from pollinator limitation. Researchers named wild bees and honeybees as important agents for pollination, including agriculturally intensive regions. The annual production value of wild pollinators in the crops included in the research was placed at more than $1.5 billion.
A Natural Yet Critical Ecosystem Service
The research study pointed out that insects as pollination agents is an essential part of crop production and by extension, food security. Previous works have estimated the value of pollinator-dependent crops is placed at $50 billion per year. However, the research on the effect of pollinator limitation has mostly focused on its effect on wild plant species, offering limited insight on its effect on crop production.
To conduct the study, researchers collected data on both insect pollination and crop production. The seven crops in the study were highbush blueberry (Vaccinium corymbosum), apple (Malus pumila), sweet cherry (Prunus avium), tart cherry (Prunus cerasus), watermelon (Citrullus lanatus), pumpkin (Cucurbita pepo), and almond (Prunus dulcis).
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Each crop was monitored from a selected study farm situated in one of the US' strategic areas in the production of that specific crop. The choice for the study farm is expected to be representative of crop production conditions - growing conditions, pollinator communities and farm management practices.
For data collection, four 100m transects were positioned in 25-meter increments during bloom. Observers also monitored small patches in between the transects to help in counting. Bee species in the study were grouped together based on hairiness and body size - criteria connected to pollen deposition capacity per visit.
Implication of Bee Population to Crop Yield in the US
Using the AIC model selection to derive the pollinator limitation frequency, the study revealed that tart cherry (in Michigan), sweet cherry (Washington), blueberry (Michigan, Oregon, and British Columbia) showed evidence of pollinator limitation, responsible for 64-94% of transects covered. Watermelon, pumpkin, and almond displayed weak evidence of pollinator limitation. The apple, observed from Michigan and Pennsylvania, a linear relationship was established, suggesting reasonable effect of pollinator limitation.
Between the pollinating agents, 74% of observed visits were from honeybees and 26% from wild bees. However, the distribution varied depending on the crop. WIld bee visits were most observed in pumpkin (74.6%) and lowest in almond (0%). The proportion of bee visits were consistent across states for each type of crop. The only exception to this observation was the watermelon, since wild bees were four times as abundant in Florida compared with California.
One of the theories behind apples, cherries, and blueberries experiencing more pollinator limitation is that their plants are intrinsically more dense in flowers compared to watermelon and pumpkin. In general, addressing pollinator limitations should increase crop yield, and food security in the US.
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