Bee Vectoring of Biocontrol Agents for Better Strawberries

John C. Sutton and Peter G. Kevan

Researchers at the University of Guelph in collaboration with industry colleagues have shown that pollinating bees can effectively deliver organic biological control agents to the flowers of strawberry plants on a field scale. It was further demonstrated that the delivered agents can strongly suppress strawberry flower blights, fruit rots and insect pests in the field. The idea of employing bees as delivery vehicles for beneficial microbes was pursued for the first time at the University of Guelph more than twenty years ago. At that time, honey bee pollinators were evaluated as vectors of a biocontrol agent (Clonostachys rosea; then called Gliocladium roseum) to suppress botrytis grey mold in strawberries in small-scale field plots. Shortly afterwards the same principle was evaluated using bumble bees in raspberry plots. The technology worked as well as, or better than, fungicide sprays and resulted in better fruit set, higher quality fruit, and longer shelf life for harvested berries. Important technological advances in bee-vectoring and biological control on various crops since then now make commercial scale use of the technology practical and feasible for growers.

In a field trial in Ontario in the spring of 2012, bumble bees (Bombus impatiens) effectively delivered the biocontrol agent (C. rosea CR-7) to four acres of blossoming strawberries. The agent provided excellent control of grey mold, Phomopsis rot, and other berry diseases. The trial represents an important step towards the commercialization of bee vectoring as a tool for direct delivery of beneficial microbes to strawberries, while the bees also serve to pollinate the crop. In this trial, four bee colony boxes were placed in the middle of the strawberry field shortly after flowering began (Figure 1). The bumble bee colonies were supplied by Biobest Canada Ltd. of Leamington, Ontario. Each colony box was equipped with a dispenser in which the bees became dusted with a powder formulation of the biocontrol agent as they exited the colony box to forage in the crop. A newly designed and patented dispenser which holds an inoculum tray for the agent and forms part of the lid of each colony box was used. Trays containing the powder formulation were replaced within the dispensers every three days, which takes very little time and can be done without upsetting the bees (Figure 2). Dusted bees subsequently deposited the powder on the flowers while foraging for pollen. On return home, the bees entered by a slightly different route which did not allow them to become dusted with the biocontrol agent.

Figure 1. A group of four bumble bee colony boxes, which were placed in the middle of the strawberry field shortly after flowering began.

Figure 2. Insertion of a tray of fresh powder formulation of the biocontrol agent into the inoculum dispenser which is located inside the bumble bee colony box.

Lab assessments showed that the bees had delivered the Clonostachys fungus to at least 80% of the strawberry flowers in the four acre field, regardless of how far the flowers were from the bee colonies. The furthermost flowers were treated as effectively as those nearest the colonies. Bumble bees are particularly effective for delivering beneficial fungi in crops in part because they visit the flowers nearly every day regardless of air temperatures and rainfall. Also important is the formulation of the inoculum powder, which was designed and tested specifically for acquisition and transport by bees, and is now patented. In this trial each gram of the powder contained at least two hundred million Clonostachys spores.

Levels of strawberry fruit rot in the bee-treated field were extraordinarily low compared to those in a nearby untreated field with no bumble bee colonies or biocontrol agent (Figure 3). Only 0 to10% (average 6%) of ripe berries in samples from the bee-treated field developed botrytis when incubated in separate plastic cells for a week at room temperature compared to 60% in samples from the untreated control field. This represented a 90% reduction in botrytis. Similar reductions were found for berries stored at 4°C for two weeks in punnets kept in a refrigerator. Phomopsis rot developed in 12% of berries from the untreated field but was not found in berries from the treated field. Rhizopus rot (whiskery rot or “leak”) was knocked down from 41% to 3%, even though there are no previous records of Clonostachys’ effectiveness against Rhizopus.

	*Grey mould (Botrytis)* incidence	*Leaf blight (Phomopsis) incidence*	*Whiskery rot (or “leak”) (Rhizopus) incidence/berry*

Treated field	strong>0 – 10%: average 6%	0%	3%
Untreated field	60%	12%	41%

Figure 3. Incidence of botrytis grey mold, Phomopsis fruit rot, and Rhizopus leak in strawberry fruit harvested from a field treated with bumble bee-vectored Clonostachys rosea compared to a nearby untreated field without the bees and biocontrol agent.

It should be noted that strawberries in the two fields in the trial were in their second year of production and were managed as organic crops. The bee vectoring technology and Clonostachys are approved for, and entirely compatible with, organic crop production.

Bee vectoring technology is becoming commercially accepted in the greenhouse vegetable production industry (especially tomatoes), but until recently had not been tested on a large scale in outdoor crops. R & D is in progress also in lowbush blueberries, cranberries, sunflowers, canola and other outdoor crops, and includes the use of biological control agents against diseases and insect pests.

In all situations tested so far, the results are positive and promising. We see numerous advantages of the bee vectoring technology for strawberry and other growers including better pollination combined with improved fruit or seed production, protection from fungal diseases and insect pests, and reduced reliance on synthetic pesticides.

Acknowledgements
The bee vectoring R & D trial was a collaborative effort among Todd Mason of Bee Vectoring Technology (BVT) of Cambridge, Ontario, Dr John Sutton, Dr Peter Kevan and Janine McGowan of the University of Guelph, and Bob Wildfong of Seeds of Diversity Canada which is based in Waterloo, Ontario. The R & D was supported by the Canadian Agricultural Adaptation Program (CAAP) of the Agricultural Adaptation Council of Canada, by Seeds of Diversity Canada, and by BVT. The formulation technology for Clonostachys was developed by Todd Mason, John Sutton, and Hamida Merwan with support of an Engage Grant from the Natural Sciences and Engineering Research Council of Canada (NSERC). The “in the lid” inoculum dispenser was developed in various stages over several years through grants from the NSERC-Engage program and other sources, and refined to present efficiency by our team working with plastics design engineers and BVT. Inquiries can be directed to Bee Vectoring Technology Inc. (beevectoring@gmail.com)