Bees for crop health
By Carolyn King
As part of a bee vectoring trial, a four-pack of bumblebee boxes is placed on a pallet at the edge of a sunflower field in full bloom.
Photo by John C. Sutton
We all know that bees are great at carrying pollen from flower to flower.
It turns out they are also great at carrying, or vectoring, microbial products from plant to plant to control crop diseases and insect pests. Based on years of innovative research and testing, bee-vectoring technology shows promise not only for Canadian greenhouse crops and fruit crops, but also for field crops like sunflowers and canola.
“With bee vectoring, there is a double benefit. Better pollination gives a crop yield boost. And then, with bees carrying biological control agents to the flowers, there is protection of the crop from fungal diseases or insect pests or both,” says Dr. Peter Kevan from the University of Guelph.
Kevan has been working on bee vectoring studies for more than 20 years, in collaboration with colleagues like Dr. John Sutton at the University of Guelph and Dr. Les Shipp with Agriculture and Agri-Food Canada (AAFC) at Harrow, Ont., and through partnering with beekeepers, crop growers, and various public and private sector agencies. Their research has received funding from the Natural Sciences and Engineering Research Council of Canada, AAFC, the Ontario Ministry of Agriculture and Food, grower organizations, private companies, Seeds of Diversity and Enviroquest Ltd.
Over the years, the researchers have developed, tested and refined bee-vectoring systems for bumblebees and honeybees, including effective, bee-safe formulations of several different beneficial microbes and practical dispenser trays for the formulations. And they have tested these systems in various crops against a number of important diseases and insect pests.
Kevan and Sutton first teamed up to work on bee vectoring in the early 1990s. “Initially we worked on strawberries and were successful in protecting strawberries against grey mould, and then protecting raspberries against grey mould, first using honeybees and then bumblebees as the vectors,” says Kevan.
Grey mould (Botrytis cinerea) is a very common fungus on fruit. These early trials showed the microbial agent Clonostachys rosea worked as well as or better than a chemical fungicide application, and the berries had a longer shelf life. Plus, the bee-vectored crops had the benefit of better pollination, resulting in bigger berries and higher yields. More recent field-scale trials in strawberries have shown the same microbial agent also effectively controls several other berry diseases.
“When John and I were pioneering bee vectoring in Canada, other people were doing similar work in other parts of the world. But the idea amongst many commercial people was that biological control didn’t work, which was a load of codswallop – there are lots of examples where biological control did work,” notes Kevan.
“But gradually things have changed, especially in the greenhouse industry. There is a lot of biological control that is commercially available to the greenhouse industry. So, when I started working with Les Shipp [in 2001], we moved very much into greenhouse uses of bee vectoring. We did some work on particularly tomatoes and peppers, and showed its efficacy against fungal diseases and insect pests.”
In greenhouses, bumblebees are generally used to pollinate tomatoes and often peppers, so it’s an easy step forward to also use the bees in suppressing diseases like grey mould and insect pests such as tarnished plant bug (lygus bug), western flower thrips, aphids and whitefly.
Kevan adds, “We are now on the verge of being commercial in the greenhouse industry. It’s not research grants supporting bee vectoring; we have forward-thinking clients who are buying the service from the commercial side.”
With this growing success in the greenhouse sector under their belts, Kevan and his colleagues are turning increasing attention to testing and refining bee vectoring for field crops in Canada, Europe and the tropics.
How it works
Bee vectoring systems use trays with powdered formulations of one or more microbial agents. A tray is attached to a managed honeybee hive or bumblebee box at the place where the bees exit. The bees walk through the formulation each time they exit and the powder sticks to their bodies in the same way that pollen sticks them. As the bees move from plant to plant, they drop particles of the product onto flowers and leaves. When the bees return to their hive or box, they enter by a different route so they don’t bring the product into the hive.
Either honeybee or bumblebee colonies can be used for bee vectoring, but bumblebees are easier. Kevan explains, “It’s mechanically a lot easier to work with bumblebees because the colonies are smaller, they have defined circular entrances and exits, and so on, rather than with a honeybee colony with 30,000 to 60,000 bees in it and a wide exit and entry space.”
So far in their bee vectoring systems, Kevan and his colleagues have been working with three common beneficial microbes: Clonostachys rosea, Beauveria bassiana and Bacillus thuringiensis.
“Clonostachys rosea is a ubiquitous soil fungus; it occurs everywhere you go in the world,” says Kevan. This fungus can control a number of important crop fungal diseases.
Beauveria bassiana, another common soil-borne fungus, is a parasite of many types of insects. “Beauveria bassiana is registered in many parts of the world for control of insect pests. All we’re doing is delivering it on the bodies of bees, rather than as a spray formulation,” notes Kevan.
“We have recently started to work with Bacillus thuringiensis, which is also registered in many parts of the world. Years ago, some bee vectoring tests in North Dakota used Bt against banded sunflower moths. Those tests were successful, but it never became a commercial use.” Bacillus thuringiensis, or Bt, is a naturally occurring bacterium; corn growers will recognize Bt as an insect control option in corn hybrids.
The economics of bee vectoring depend on such factors as the crop, the problem to be controlled, the grower’s practices, the location, and the costs for the bees and the microbial product.
When Kevan and his colleagues talk to farmers at bee vectoring workshops, they find a lot of interest in the technology, especially among organic farmers. “Bee vectoring isn’t per se designed as an organic farming technology, but everything we’re using can be certified organic,” he explains.
He adds, “It’s simple enough to fit into a conventional farming system as long as the farmer is aware not to spray when the crop is blooming. Insecticides should not be used at the same time as bees are around being used to vector the biocontrol agent [the bees will likely be harmed or killed], and use of chemical fungicides should be avoided because the biological control agents are living fungi.”
Recent field crop experiments
The researchers have conducted a number of field experiments in sunflowers and canola. For example, in 2011 and 2012 in Ontario, they used bumblebees to deliver two microbial agents in sunflowers. Clonostachys rosea was used for control of Sclerotinia sclerotiorum, a very common crop pathogen, which causes sunflower head rot. And Beauveria bassiana was used simultaneously to control banded sunflower moth.
Those trials were very successful. Sclerotinia severity was reduced by 70 to 100 per cent in the bee-vectored fields. As well, other fungal diseases, such as Botrytis, Fusarium and Penicillium were also greatly reduced. Banded sunflower moth populations were below economic loss levels in treated fields. As well, the bees’ pollination services were also very valuable – Kevan points out that, even though modern sunflower varieties can be self-pollinated, the seeds from cross-pollinated plants are bigger and weigh more, have a higher oil content, and have much higher germination rates.
The combination of crop protection and better pollination in the bee-vectored sunflower fields resulted in an average yield boost of more than 20 per cent. The bee vectoring system also provided a four-fold return relative to the costs of the bumblebee colonies and trays of the microbial powder.
In 2014, the researchers are hoping to do more sunflower trials in Ontario and to start some in Manitoba.
In canola, their first field experiments were conducted back in 2002 and 2003. Dr. Mohammad Al-Mazra’awi, a Jordanian national who was then a PhD student at the University of Guelph, used honeybees as vectors for Beauveria bassiana to control lygus bugs. He found that lygus bug mortality was about 50 per cent with bee vectoring compared to about 10 per cent without bee vectoring. But at about that time, the researchers started focusing more and more on the greenhouse industry, so their canola studies were put on hold.
Now, the researchers are getting back into canola. In fact, they had a big field trial established in 2013, but a major hailstorm destroyed the crops and the hives, so they weren’t able to obtain any data.
“We would very much like to get co-operators who would like to test our technology with sclerotinia on canola; it is such an important canola disease,” notes Kevan.
He emphasizes that field-scale trials are crucial. “We have to show to the growers that, first of all, bee vectoring works at the field scale, and then, of course, it has to be shown to be economically feasible.”
Even without the bee vectoring benefits, bee pollination could potentially boost canola yields. “Small experiments have been done all over the world – in Quebec, Ontario, recently in southern Brazil, in Europe, etc. – and they all have shown that, if honeybees are placed on canola fields, yield boosts are between 15 and 30 per cent,” notes Kevan.
Another possible use of bee vectoring in canola would be in the production of hybrid canola seed. Hybrid seed production relies heavily on bees for pollen transfer between the parent plants, so bee vectoring would be an easy fit.
Along with their plans for further work on sunflowers and canola, the researchers have a number of other bee vectoring projects in the works such as a pilot project with coffee crops in Brazil, greenhouse studies for controlling cabbage looper, a pilot project to manage fire blight on apples and pears in Nova Scotia, and a study to quantify the increased shelf life and shipping life benefits for fruit.