Project Details:

How Much Do Soybeans Benefit From Honey Bee Pollination (and Vice-Versa)? (Year 2 of 1520-732-7225)

Parent Project: How Much Do Soybeans Benefit From Honey Bee Pollination (and Vice-Versa)? (Year 1 of 1520-732-7225)
Checkoff Organization:United Soybean Board
Categories:Sustainability, Crop management systems
Organization Project Code:1620-732-7225
Project Year:2016
Lead Principal Investigator:Matthew O'Neal (Iowa State University)
Co-Principal Investigators:

Contributing Organizations

Funding Institutions

Information and Results

Comprehensive project details are posted online for three-years only, and final reports indefinitely. For more information on this project please contact this state soybean organization.

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Final Project Results

Our project had four activities that addressed two simple questions: Do bees benefit soybeans and do soybeans benefit bees? These questions were divided into a set of four objectives.

To answer these questions and address the objectives, we worked with ISU research farms and commercial farmers in central Iowa to use their fields to measure several components: the abundance of honey bees and native bees in the fields, and their potential yield impact to soybeans. We identified soybean fields in simple (surrounded by less than 25% non-crop habitat) and more complex landscapes (more than 50% non-crop habitat). By sampling the bees in these fields, we determined if landscape affects bees in soybean fields. In both 2015 and 2016, we found ten fields in each of these two landscape types. In half of each landscape type (n=5), we placed four honey bee hives. In total, we had twenty fields, ten with honey bee hives and ten without. By developing these four field types (with and without honey bees, simple vs complex) we could determine if adding honey bees altered the community of bees in the field and the yield of the plants.

In addition to this field experiment, we conducted laboratory studies to determine the impact of foraging on soybean on honey bees. Due in part to unforeseen difficulties noted below (no soybean pollen was collected, project was not funded for the third year), we were unable to complete all of the experiments described in the original proposal. Data collected from the field and lab experiments are summarized below.

Question 1: Do bees benefit soybeans?

Objective 1: Characterize the impact of landscape on the bee community that visits soybeans.
Because the surrounding landscape affects insects in soybeans, we hypothesize that this factor will influence the abundance and diversity of bees in soybean fields.

Findings: During 2015 and 2016 we consistently observed the most honey bees in soybean field in which we placed hives at a field edge, with no difference between landscape type. For fields that did not receive hives, we found more honey bees in fields within landscapes surrounded by mostly non-crop habitat (i.e. complex), but this difference was not statistically significant. We also found native bees in all of the soybean fields, even those in which we placed honey bee hives at the field edge. We have accounted for all of the native bees collected in 2015, but not 2016 as identification continues. The abundance of native bees observed in fields was not significantly affected by the presence of the honey bee hives. Placing honey bee hives next to a soybean field increased the abundance of honey bees found in the fields and in 2015 this occurred without a significant impact on the native bee community.

Objective 2: Determine if soybean yield is greater when soybeans are exposed to pollinators.
Within each field we selected 20 individual plants. Half of these plants were caged during bloom so we can compare yield differences when bees had access to the soybean flowers. In 2016, to prevent soybean aphids from affecting our yield estimation, we hand-planted aphid-resistant varieties of soybeans into the fields. In addition, we released a parasitoid of the soybean aphid at all sites to further limit the impact of the soybean aphid. To estimate the yield, we measured the weight of seed from both selected fields.

Findings: Our yield data were not consistent between the two years.

In 2015 we observed a remarkable difference between caged and uncaged soybeans. We expected a higher yield from plants left uncaged compared to caged plants, as the cage prevents bees from visiting the flowers. Contrary to what we expected, caged plants had a higher yield than uncaged plants; caged plants averaged 39% greater seed weight than uncaged plants. We hypothesized that since none of the fields were sprayed with insecticide, soybean aphids and possibly other insect pests reduced yield on the uncaged plants as they would have access to those plants.

In 2016 we used soybean aphid-resistant soybeans in an effort to prevent soybean aphids from affecting our estimate of yield without not using insecticides. We hand-planted this variety into the commercial fields and compared the yield on both caged and uncaged plants. Using this variety decreased the difference between caged and uncaged plants by over half, but the caged plants still had a higher yield. In 2016, on average caged plants 18% greater seed weight than uncaged plants. To what extent other factors altered the yield (other insects, a ‘cage’ effect, etc) is not known.

Despite the unexpected effect of the cages in both years, we did notice a remarkable trend in uncaged plants. In 2016, we observed an increase in yield when soybean fields had honey bees adjacent to them compared to those with only native bees. However, during our second year, the presence of honey bees next to a soybean field was not associated with a difference in yield.

Also, based on seed weight, we estimated a higher yield in 2015 than 2016. This is interesting as it suggests that the impact that bees may have on soybean yield may be a function of the yield potential within a given year. The impact of pollination on yield may only be noticeable when the plant is reaching its’ full yield potential. When the plant experiences stress, the yield improvement from pollination may not be observed. Future research should investigate the role that plant stress (water, heat, insect damage) may prevent bee pollination from improving the yield of soybeans.

Question 2: Do soybeans benefit bees?

Objective 3. Determine the extent to which bees utilize soybeans for pollen and nectar and the effects of soybean flower foraging on colony health.
Although beekeepers in the Midwest claim that much of the honey produced is from nectar collected in soybean fields, there is little empirical evidence to support this claim.

Findings: In both years, we did not find soybean pollen in traps placed on twenty of the hives placed next to soybean fields in central Iowa. The amount of pollen collected from other plants did not vary by landscape. We did find pollen from several plant species, with clover and partridge pea comprising over 70% of pollen brought to the hives. We did find soybean pollen in honey samples taken from hives. This observation and data from our bee bowls suggest that honey bees are foraging within soybean fields. Furthermore, honey bee hives gained weight during the bloom period of soybeans. After soybeans stopped blooming, the hives began to lose weight. This indicates that the nectar collected from soybeans contributed to hive growth and that regardless of the landscape, there was limited forage available after soybeans bloomed.

Soybeans are a source of nectar for honey bees and when in bloom can help hives grow. However, once soybeans are no longer in bloom, there is very little forage for honey bees. This is very interesting to beekeepers and those studying the declining health of honey bees, as it reveals a lack of forage very early in the growing season. These data suggest that honey bee health and survival could be increased if a late summer/early fall forage was made available. To what extent such forage could remove the negative impacts of pathogens (like viruses) and pesticide exposure is the subject of our next series of research, funded by the USDA (see below for more details).

Objective 4. Determine the nutritional and health value of soybean honey and pollen to caged honey bees.
Using small cages of honey bees in a laboratory, we performed a more fine-scale investigation of the health effect of pollen collected by honey bees in our field experiment. This experiment tested the nutritional value of the pollen on the immune system of worker honey bees.

Newly emerged honey bees were collected from colonies in an apiary managed by Dr. Amy Toth at Iowa State University. These bees were randomly assigned to small plastic cages with 30 bees per cage. Each cage was assigned a treatment of four pollen diets that allowed bee to feed ad libitum. “Non-pollen” was the negative control, with no pollen and only corn syrup was provided to honey bees. “Soybean field pollen” and “prairie pollen” were mixes of pollen from multiple plant species collected from colonies next to either a soybean field or prairie in central Iowa in June of 2016. Chestnut pollen (Castanea sativa) was imported from France and considered as positive control, as previous studies indicate that it can improve honey bee immune systems leading to reduce mortality when exposed to viruses. Honey bees were infected with viruses by providing bees with 50% (v/v) cane sugar syrup containing virus for the first 12 hours and clear 50 % syrup were provided to bees until the end of test. The pollen was renewed and dead bees were recorded and removed every 24 hours.

Findings: Honey bee mortality was greatest when bees were exposed to the virus cocktail, and honey bee survival was not affected by diet. This result is surprising as previous experiments revealed that the Chestnut pollen reduced the impact of the virus infection. Unlike previous experiments, the bees used were collected late in the summer (August to September). Future experiments will work with bees collected earlier in the spring, which may be healthier and respond more strongly to the various diets.

The results are not consistent with previously published studies, therefore it is hard to interpret their impact for farmers. At this point, it does not appear that pollen collected by bees near soybean fields increases honey bee mortality compared to the other pollen diets treatments.

Project Years