2023-07-09 23:09:00
Bumblebee colonies are used by farms to pollinate, with unintended consequences
When Olivia Miller peeked inside the bumblebee nest boxes, she expected to find a single queen amidst a sea of workers. She hadn’t expected to find a handful of dead bumblebee queens strewn about the nest.
At the time, Miller was studying applied ecology and environmental science at Cornell University. She was also part of a group of researchers investigating whether introducing bumblebees raised in commercial settings could boost pollination on farms that grew strawberries early in the season (in May, when pollinator numbers tends to be low), then tomatoes later (when pollinators are more abundant).
The team was convinced that adding commercial bumblebee colonies would lead to better pollination. Bumblebees are more effective at pollinating certain crops than honey bees, in part because of a behavior called buzz pollination, says Heather Grab, associate professor at Cornell’s School of Integrative Plant Science. “They latch onto a flower with their mandibles, and then they vibrate their flight muscles without actually moving their wings, and that releases pollen from the anthers of some really specialized kinds of flowers. »
Tomatoes are particularly known to benefit from buzz pollination. But, to their surprise, the team found that tomato plants in fields with commercial colonies of bumblebees actually received fewer bee visits than plants in fields without. However, not all bee species appeared to be affected. While common oriental bumblebee visits (An impatient bombshell) fell in number, unlike those of other bee species. Eastern common bumblebees are commonly seen in the wild in eastern North America and are also the same species used in commercial colonies.
And then there was the mystery of dead wild bumblebee queens, most of which were also common oriental bumblebees. “Very soon after placing commercial colonies in the field, we started to see these very large numbers of dead queens accumulating there,” Miller says. “It was very unexpected and very concerning. »
These findings, which they recently reported in the Appliqué Journal Ecology, prompted them to investigate further. “It really kicked the project off in this whole other, I think, probably more important direction,” Grab says. The team studied bumblebee behavior and found a potential explanation: when bumblebee queens are looking for a nesting site, they can either create their own colony or ‘usurp’ an established colony by sneaking up and replacing the resident queen. . This usurping behavior usually occurs in the spring, when bumblebee colonies are still establishing themselves and few workers are defending the nest. Thus, in nature, attempts at usurpation often succeed.
As the commercial colonies were full of workers, if the wild queens attempted to usurp, they were immediately overwhelmed by massive numbers of worker bees. This unfortunate moment resulted in fewer bumblebee colonies in the area. “Each of these dead wild queens is a queen that could have potentially created her own colony and produced workers that would have pollinated later flowering crops,” Miller says. Commercial bumblebee colonies actually reduced pollination of certain crops by acting as death traps for wild bumblebee queens.
This is a situation where timing is everything. In spring, when wild bumblebee queens search for nests, commercial colonies are also set up to pollinate early season crops. “The natural cycle of bumblebees means that at this time of year we just don’t have a lot of them,” says Karen Goodel, an ecologist from Ohio State University who was not involved in this study.
This usurpation effect gone wrong is far from the first instance in which commercially bred pollinators have resulted in unintended consequences for an ecosystem. Sydney Cameron, an entomologist at the University of Illinois at Urbana-Champaign who was not involved in this study, explains that disease transmission from commercial bees may have contributed to the decline in wild bumblebee populations. But, she adds, “I don’t think we’re going to get rid of commercial bees, because farmers want them and because wild bees have declined due to habitat loss.” Cameron says large-scale farming has pushed wild bees out of their former habitats, making it harder for farmers to pollinate their crops. “They probably, in some cases, need improved commercial bees,” she says, “but they don’t need to have that many and that density. »
Miller, Grab and the other researchers began to think of a queen excluder, a small plastic device that reduces the size of the opening so that bumblebee queens cannot squeeze through, unlike smaller worker bees. The grids are designed to keep the resident queen inside the box, but the researchers thought they should also be useful in keeping feral queens out.
The team set up eight large weatherproof containers, each containing two commercial colonies – one with a queen excluder and one without – and distributed them among eight apple orchards. After two weeks, they retrieved the nest boxes from the containers and counted the number of dead queens inside. On average, they found 10 dead bumblebee queens in each nest box without a queen excluder device. Three wild queens also died in a box with a queen excluder, but only during a two-day period when the device was set incorrectly. When used correctly, queen excluder devices are 100% effective in preventing usurpation attempts, and therefore death, of wild bumblebee queens in the area.
The team also considered whether there might be any downsides to adding queen excluders. They counted and measured the bees in each colony and found no effect of queen excluders on the number or size of worker bees or on the survival of the resident queen. The outcasts seemed to eliminate the problem of accidentally trapping wild bumblebee queens, without causing further problems for commercial colonies.
The team now hopes the bumblebee industry will adopt widespread use of these devices to help protect wild bees and maximize crop pollination. “It’s a very simple, inexpensive and easy-to-implement solution. So hopefully they will become the norm,” says Miller. “Especially since we have shown that there are no negative effects on the commercial colony,” she adds. “Producers can only benefit from their use. »
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