EDMONTON — Up to 95 percent of seed canola yield is attributable to bee pollination, but it’s not known how much pollinators influence yields in commercial hybrid canola crops.
“This is where I come in,” Alberta Agriculture researcher Shelley Hoover told Murray Hartman’s Science-O-Rama in Edmonton April 6.
“Part of my research program focuses on bees and bee health, but a substantial part of my work focuses on canola pollination and pollination management.”
Many studies have been conducted into what bees contribute to canola yields, and their findings vary widely. Some studies show bees have little effect on hybrid canola yields, while others describe a strong relationship between the two.
Hoover said a study that researcher Rachid Sabbahi conducted in Quebec in 2005 examined canola yield from plants pollinated three ways:
- grown in a cage so the plants could only self fertilize
- grown out of a cage so they could pollinate by wind but not bees
- exposed to bee concentrations of .6 colonies per acre and 1.2 colonies per acre
Plots that allowed wind pollination yielded better than plots that could only self-pollinate, and the plots where both wind and bees were allowed had a further increase in yield.
“They found the seed yield increase of 46 percent at a stocking rate of three hives per hectare (1.2 hives per acre), which works out close to 200 hives per quarter,” Hoover said.
“If you extrapolate that out across the Prairies, if you can get 46 percent yield increase all the way across the Prairies, we’re talking billions of dollars.”
There are more beehives in Canada then ever before, but 25 million honeybee colonies would be needed to expose 21 million acres of canola at 1.2 colonies per acre.
There are currently 490,00 colonies on the Prairies.
The economics of having that many hives is unfeasible, but Hoover said there are opportunities to learn how to use bees more effectively.
Hoover also talked about a Lethbridge study that looked at pollinator abundance in canola crops, their distribution across fields and how that relates to yield.
There were three treatments:
- canola plots had to self-pollinate without wind
- wind was allowed but not pollinators
- wind and pollinators were allowed
Some of the plants in each treatment received maximum pollination by hand, while the rest of the plants were not hand pollinated.
No significant yield differences were seen between hand-pollinated plants and unpollinated plants in terms of seed yield.
“So that tells us in these open plots there is no difference between the maximum pollination that can be achieved with hand pollination and just what they are getting by being in the environment,” Hoover said.
The treatment with wind but without bees also saw no difference between the maximum hand pollination and the yield benefit they received from wind alone.
However, the treatments that used wind-excluding tents saw a significant difference between hand pollinated and un-pollinated plants.
“So what that tells us is that there is a pollination deficit in this instance when wind is excluded, she said. “When you exclude wind, the plants are not fully pollinated, but when you exclude bees, in this case they were.”
Hoover said Lethbridge is a windy area and pollination from wind may play a disproportionally large role in the area. Calmer locations may not see the same results.
A 2015 study that Lorenzo Marini supervised at the University of Padua in Italy used three hybrid cultivars and three open pollinated cultivators.
“Whether or not you put bees on the hybrid cultivars, it didn’t make a difference,” Hoover said.
“With the open pollinated cultivators, there was a significant increase in yield when they added bees.”
The study examined 43 fields over two years, but the mean field size was only 34 acres.
The three European hybrid rapeseed varieties in the study, Catalina, Excalibur, and PR45D01, responded differently to the addition of pollinators.
“With Catalina if you add insects, you see an increase of yields over no insects, but in these other two varieties, you don’t,” Hoover said.
The study also found that insects can make up for some of the effects seen from not fertilizing in trials with zero fertilization.
“In this case, at no fertilization the insects basically brought the yield up to the level that they would have seen if they had fertilized,” Hoover said.
Insect pollination also affected seed size, which she said she has noticed in previous studies.
“When you have abundant pollinators, you tend to get lots of seeds but they are smaller,” she said.
An Alberta study examined the types of pollinators in the province’s commodity canola crops by looking at pollinator abundance, their abundance in relation to the field edge and if the abundance of the pollinators related to the nectar concentration in the flowers.
There was regional variance in the types of pollinators, but flies and honeybees were the most common.
“I’ve had growers tell me they like to have fields near feedlots because there are so many flies. They can be effective pollinators,” she said.
Fields stocked with honeybees had more bees, but there was a large variation in how the bees were distributed across the field.
“So you might have 300 visits per hour to a metre squared, or you might have close to zero,” Hoover said.
The further away from the hive, the less visits the canola blooms received from bees.
“Even at 100 metres into the field, you see a decline, and by the time you get 500 or 400 metres into the field, it’s not significantly different than not stocking the field,” Hoover said.
Canola plants in the middle of the fields also received fewer visits from wild pollinators because they have a shorter flight range than honeybees.
A greater nectar reward was found at the centre of a canola field, but bees would take a nectar reward closer to the hive if they could.
Another pollinator study held in the Lethbridge area examined the efficiency of bees in seed canola crops by looking at the amount of pollen deposited on the stigma of the flower.
The study found that the amount of pollen deposits depended on where the bee came from.
Bees coming from the male flowers were a lot more likely to deposit pollen in the next female flower it visited than bees that entered a female flower after being in a female flower.
Hoover said they are now looking for ways to distribute bees to encourage them to switch from male flowers to female flowers.
The study found no significant difference in the amount of deposited pollen between honeybees and flies and male leafcutter bees.
Female leafcutter bees are the workhorses in terms of depositing pollen per individual bee visit, but bumble bees work longer hours and when it’s colder, Hoover said.
As a result, it’s beneficial to have a variety of pollinators that work under different conditions.
“As you increase the number of bee species, independent of bee abundance, you see greater yields just because the bees work the flowers differently,” she said.