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Nutritional stress caused by increasing loss of floral resource abundance as well as diversity in the landscapes can impact the growth of bumblebee populations, according to a study.
This, in turn, can threaten the production of foods such as tomatoes and strawberries, cranberries, peppers, eggplants, and potatoes as bumblebees are known to be important pollinators, the researchers said.
“If we didn’t have bumblebees, you could grow tomatoes but not on the scale needed to, for example, add enough lycopene to the human diet — an antioxidant that protects cells in our bodies from damage,” said Hollis Woodard, assistant professor of entomology at University of California-Riverside, in an article on the university's website.
"Bumbles are at the crux of how we live today, and how we’ll live in the future,” she added.
While exposure to insecticides and global warming have affected bumblebees' population, the study focused on how composition of pollen diet can impact early nesting success in laboratory-bred queens of the bumble bee Bombus impatiens. The study was published in the journal Environmental Entomology.
In an experiment, the queen bees were fed three different plant diets. The results showed that diet does not affect the number of eggs a queen might lay, or how quickly she starts laying eggs. Of the three diets, only one was found to be better for the broods (or eggs) to mature in to adulthood.
Bees develop in four distinct life cycle phases — egg, larva, pupa, and adult. Difference of days to hatch classifies the bees into queens (16 days) , worker bee (21 days) and drones (24 days). The queen’s eggs need to be fertilised for a female bee (worker) to hatch, while drones (males) are the result of unfertilised eggs.
The findings suggest that diet compositions may delay larval growth, and can ultimately delay the development of young nests.
“Without a variety of pollens available, the queens are constrained to fewer options, some of which appear to be bad for them," Woodard said. “Bees need diverse diets just like we do, and they suffer when they don’t get.”
Moreover, as compared to many other bee species that nest year-round, including honeybees, bumblebees have an unusual life cycle.
"In summer, the queen and her workers are social, collecting food for the colony. The colony dies off at the end of the season, and only new queens are alive at this stage. If the queens mate successfully, they will hibernate like bears. In spring, the queens re-emerge to collect food, look for nests and lay their eggs — up to 400 of them. During this time, the queens bear the sole responsibility for foraging, feeding, protecting all the eggs, and maintaining the nests," the study said.
“For every queen that doesn’t start a nest successfully, there are hundreds of bumblebees lost. The consequences scale up fast,” Woodard said.
Unfortunately, at least one species of bumblebee is already on the endangered species list. Four additional species native to California are also being considered for state listing, Woodard noted.
The study sheds light on how "one of the leading stressors for bumble bees (nutritional stress) may negatively impact populations through its influence on brood production during the nest-founding stage of the colony cycle," according to the study.