Michigan researchers, following two years of study, continue to be encouraged by the potential of a new bee for tree fruit pollination. The hornfaced bee (Osmia cornifrons) was originally studied as a potential pollinator for Balaton cherries to see if fruit set could be increased. Balaton, a sweet tart cherry, has suffered from poor yields, particularly during years with cool, wet springs.
"We started with Balaton," said Dr. Nikki Rothwell, coordinator of the Northwest Michigan Horticultural Research Station in Traverse City. "Now we’re looking at other crops like apples." Rothwell reported on research results during the Great Lakes Fruit, Vegetable, and Farm Market Expo held in Grand Rapids, Michigan.
According to literature, the hornfaced bee is used to pollinate about 85 percent of the apples produced in Japan, she said.
The hornfaced bee, related to the mason bee, is very different than honeybees used to pollinate most tree fruit crops, Rothwell noted. Researchers have noticed three primary differences between hornfaced bees and honeybees. Hornfaced bees forage for a significantly longer amount of time per flower than honeybees, and they visit significantly fewer flowers per tree than honeybees and fewer flowers per minute. Thirdly, they fly under slightly different conditions than honeybees.
"Hornfaced bees are active in early spring, and growers can put buckets of bees out when they need pollination," she added. Males emerge from their overwintered nest first, followed by females ready to mate. Lots of mating between the bees initially takes place, but eventually the males and females collect pollen for egg laying and nest building.
Rothwell said that data so far shows that hornfaced bees are comparable to honeybees in regard to pollination, although data has been hard to quantify because it is difficult to keep other bees out of orchards under study. Trials are set up by dividing an orchard in two and placing hornfaced bees in one half. Four of eight orchards had better yields, but increased yields were not statistically significant, except in one.
"But overall, I know that hornfaced bees are comparable," she said.
Researchers are trying to learn the timing of bee placement in the orchard, believed to be critical for pollination success. Data suggests that the optimum timing is between 160 and 215 growing degree days, but scientists are working to narrow the number down further.
They are also studying foraging efficiency and efficacy and foraging activity under different weather conditions. They will continue to assess the influence of pollinators on tree fruit yields.
One of the major benefits of using hornfaced bees is that the grower could have his or her own supply of bees and wouldn’t have to rent bees every spring. Rothwell wants to identify management practices that lead to successful recolonization of the nests, such as painting the ends of the tubes that the bees nest in so growers can see when emergence takes place.
They have found that placing the tubes inside five-gallon buckets and hanging the buckets horizontally in an apple bin placed on its side helps the hornfaced bee find its nest inside the orchard. "They need to have a good visual cue in the orchard," she said.
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