Orchards and bees

When Growing for Green initially proposed planting a community orchard in Ben Nobleman Park, some residents were concerned that the fruit trees would attract more bees and that those bees would be a threat to children and others. In response, our volunteer Benjamin Langer, an expert in soil sciences, researched this topic. Read more below:

The Effect of Fruit and Flower Trees on the Presence of Bees in Ben Nobleman Park, and Consequences for Health and Safety

Benjamin Langer, BSc. Biology

Introduction

Flowering plants make up the vast majority of existing plant species, approximately 90-95 percent of an estimated 287,000.  While within this enormous group there is a wide variation in size, form, life cycle, habitat and ecological niche, all flowering plants share one basic necessity: they are dependent on animal pollinators for sexual reproduction.  The most important pollinators of flowering plants are bees, which themselves comprise at least 20,000 to 30,000 species worldwide.  All of the trees proposed to be planted in Ben Nobleman Park depend at least in part on bees for pollination, and will therefore attract them.  As some species of bee and wasp are capable of stinging humans when aggravated, there is concern that planting these trees will increase the risk of bee stings.  The purpose of this article is to explore the potential risks of the Ben Nobleman Community Orchard with regard to bees and other pollinators.

The Issue

Will the planting of fruit and flowering trees in Ben Nobleman Park increase the risk of bee stings to those using the park?

This question has two distinct components that can be answered separately.  The first is whether planting fruit trees will increase the abundance of stinging bees and wasps from the current baseline level.  The second is whether such an increase will lead to an increased risk of bee and wasp stings to those using the park.

Discussion

While there is currently no data available on the diversity and abundance of pollinators visiting Ben Nobleman Park, and data in this regard is scarce for Toronto, a 2004 study by Tommasi and colleagues at Simon Fraser University, which surveyed diverse Vancouver habitats for diversity and abundance of bee populations, can provide some useful data.  It would be valuable to have information specific to Ben Nobleman Park, but in lieu of this information the SFU study allows us to generate a likely baseline estimate.  It must be noted that major sting threats come from two  sources – the European Honey bee (Apis mellifera) and the yellow jacket (Vespula sp.), which is actually a wasp and therefore not included in the SFU study.  Other species of bee are either stingless or only sting when severely physically aggravated.

Tommasi et al (2004) found a total of 56 different bee species across the sample sites throughout the city of Vancouver, with the highest diversity of bees in wild areas.  While the most common bee encountered was Apis mellifera, this bee accounted for less than half of the total bee encounters in the study.  In the traditional landscaping category, an average of 22 bee encounters per hour was recorded, of which 6 on average were Apis mellifera.  This category also exhibited the lowest diversity of non-Apis bees.  In the city gardens, an average of 78 bee encounters per hour were recorded, of which 22 were Apis mellifera.  Gardens exhibited the highest bee encounter rate.

While it would seem from this study that the proposed Ben Nobleman fruit trees might increase the abundance of the stinging Apis mellifera, it must be kept in mind that in the SFU study’s garden category almost all of the land area was taken up by fruit and vegetable production and the sites also housed managed Apis mellifera hives and mason bee nests to promote pollination.  In the case of Ben Nobleman Park, the fruit trees will take up very little of the land area and no managed bees will be present.  Further, many of the traditional landscaping plots had ‘few or no weeds,’ which is not the case with the park.  The SFU study recorded the species of plant from which every bee was collected, and the majority were collected off of wild or cultivated flowering herbaceous plants.  Therefore, while the proposed fruit trees will certainly attract bees, they will do so no more than any other flowering plant and will be responsible for only a small fraction of total bee visits to the park.  Bill Freedman, an urban ecology professor at Dalhousie University, said that “Unless the neighbourhood is presently a floral desert, it is unlikely that planting flowering trees will increase the abundance of bees and wasps.”

Though this may be the case, there will be periods of time, when the fruit trees are in full bloom, when there will be a great number and diversity of pollinators visiting them in search of nectar.  Freedman notes that “for a few days of the year it may focus their activity on that nectar source” but that “without the activity of those and other pollinators, no fruit would be gained from the trees.”  Does this increase in bee abundance around the trees mean a greater likelihood of stings to those in their proximity?  Dr. Mark Winston, a professor of apiculture and social insects at Simon Fraser University, says that this is not the case: “bees foraging on flowers pose almost no risk for stinging.  Unless disturbed, and it takes quite a bit of disturbance and agitation, bees ignore people when they are foraging. Their search image is for flowers, and bees rarely sting away from the nest (and actually don’t sting much near the nest). And, bees will only be visiting the trees for the week or two they are flowering; bees have no interest in fruit trees outside the flowering season.” To prevent bees from having any interest, avoiding bright, floral patterns and strong perfumes is therefore suggested.  But even if this advice is not heeded and bees should take an interest, Winston noted further that the major factor in sting risk is not the abundance of bees but human behaviour: “bees and even wasps are not aggressive away from their nests, and most stinging occurs when people panic and flail around, or step on a bee or wasp.”  Most stings will come from wasps, not bees, and Winston said that wasps will especially be attracted by rotting fruit.  This problem can be solved by making sure to collect ripe fruit in a timely manner: “There is much more likelihood of wasps stinging around garbage, or barbeques, than in a well-tended orchard.”

Conclusion

Bee and wasp stings are certainly a health and safety concern to our community.  It should be clear, however, that the Ben Nobleman Community Orchard does not increase the baseline risk of stings.  Much more progress can be made through proper waste management in the park and an education campaign regarding sting prevention.  The Community Orchard would be in a very good position to carry out such education about pollinators and other park wildlife, as well as bee and wasp safety.

References

Désirée Tommasi; Alice Miro; Heather A Higo; Mark L Winston. “Bee diversity and abundance in an urban setting” Canadian Entomologist; Nov/Dec 2004; 136, 6; CBCA Complete pg. 851

Dr. Mark Winston.  Personal Communication.  May 10th, 2009

Dr. Bill Freedman.  Personal Communication.  May 11th, 2009