Recently, the abundance and variety of wild insect pollinators have significantly decreased globally. This poses a threat to the ability of crops to produce enough food for the rapidly growing human population. With fewer wild insect pollinators, crops that rely on animals to spread their pollen will be limited in their ability to reproduce and thus will likely produce a smaller crop yield. European honeybees are often used to assist the pollination of crops, but the research of Garibaldi et al. (2013) suggests that this strategy may not be the most effective for food production. Garibaldi et al. investigated the amount of pollen the wild insect pollinators and the honeybees deposited on flowers and the mean fruit set of crops around the world to determine if wild insect pollinators and honeybees enhance pollination of flowers and increase the fruit set of crops. The results imply that, while both wild insect pollinators and honeybees increase pollination of crops, the wild insect pollinators pollinate crops more effectively than honeybees and honeybees are not a substitute for wild insect pollinators, but a supplement. In lieu of this, the intentional management of a combination of wild insect pollinators and honeybees may improve global crop yields. —Lia Metzger
Garibaldi, L.A., Steffan-Dewenter, I. Winfree, R., Aizen, M.A., Bommarco, R., Cunningham, S.A., Kremen, C., Carvalheiro, L.G., Harder, L.D., Afik, O., 2013. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science 339, 1608-1611.
Garibaldi et al. studied the pollination and fruit sets of 600 fields in 41 crop systems in 19 countries in all regions of the world except Antarctica. The authors studied pollinator-dependent crops of annual and perennial nuts, seeds, and fruit crops to account for a wide variety of crop types. Crops varied in management practices, landscape styles, abiotic and biotic factors, and native and non-native ranges. Many factors could affect the trends for pollinators, so Garibaldi et al. standardized the crop systems from which they collected data. Each of the crop systems consisted of the same species but from at least three spatially separated fields with similar management. This reduced the possibility of random factors significantly affecting the results.
The authors created strict criteria to consistently count the visitations by an assemblage of wild insects to crop flowers in the sampled fields. Pollen deposition was calculated as the number of pollen grains per stigma and fruit set was determined by the percentage of flowers setting mature fruits or seeds. In order to analyze whether the wild insect pollinators and the honeybees enhanced the crop yield, the pollen deposition for each insect species was compared with the resulting mean fruit set of each field. The variation in space and time of pollen deposition and fruit set was accounted for as the coefficient of variation (CV). Descriptive and explanatory graphs with CV for each species of crop and assemblage of wild insect pollinators and honeybees were included.
The study found that crops with more visits from wild insects and honeybees had more pollen on their flowers than crops with fewer visits. Honeybees were responsible for more pollination than wild insects by 74%. This did not match the prediction that crops pollinated by honeybees would have higher mean fruit sets. On the contrary, for all crop systems visited by wild insects, fruit set increased significantly, whereas fruit set only increased in 14% of the crop systems with only honeybee visitation. Disparate visitation and unequal abundance were shown not to be factors that could have affected this trend.
Increased pollinator visitation, however, did not result in as significant an increase in fruit set as the pollen disposition on flowers. The authors considered pollen excess, seed abortion, and filtering of pollen as possible reasons for the visitations not always resulting in pollination. The results suggest that wild insects were more efficient pollinators than honey bees because the difference in pollen disposition and fruit sets was much wider for honeybees than for wild insects. In addition, fruit sets increased in crop systems with visitation by wild insects, whether honeybees visited frequently or not. In crops with both wild insects and honeybees, the fruit sets increased more than crops without honeybees. These results suggest that honeybees supplement the pollination of crops by wild insects but cannot replace it.
The increase in fruit sets with more visitations by wild insect assemblages and honeybees suggests that the integration of managed pollinators with wild pollinators could produce better crop yields. The authors found that wild insects more effectively pollinate crops while honeybees pollinate more with less results. Since there was no negative correlation between the two pollinators when they visited the same crops, integrating the pollinators would likely produce more crop yields. The consideration of wild insects as part of the management of crops could encourage diversity of animal pollinators and increase food production globally.