Sunday, May 3, 2015

Pollen shortage a major threat to honeybees

There have been lots of breathless reports about the decline of honeybees, but no consensus on the cause.

A new study suggests it’s not so much pesticides, although they play a role. And not entirely parasitic pests, another favorite bad guy. 

(Image:  A honeybee settles onto a wildflower. Photo credit: U.S. Department of Energy Fermi National Accelerator Laboratory.)

But nutrition. The youngest bees may simply not be getting enough nutritious food to eat, causing impacts for the rest of their lives. Specifically, not enough pollen.

That’s a conclusion of a paper in the journal PLOS ONE, by Hailey Scofield and Heather Mattila, both of the Department of Biological Sciences at Wellesley College.

It's a major discovery, since pollen shortages have not been at the top of anybody's mind with regard to the national loss of bees called colony collapse disorder. It's not even mentioned on the Fish and Wildlife Service web page on the loss of honeybees.

To be clear, parasites, pesticides and diseases are threats—but they’re bigger threats for a weak bee, the authors of the new paper say. 

“A chief concern about the impact of poor nutrition on honey bee colonies is the possibility that it acts synergistically with other environmental stressors to undermine colony function. Notably, undernourished larvae are particularly vulnerable to some of these stressors, including pests, pathogens, and pesticides,” they write.

A hive’s pollen resources can be limited because it’s not flowering season, or because the habitat is poor (just not enough flowering plants around), or because the hive is being so aggressively managed that the bees for one reason or another don’t collect enough pollen—“commercial management practices that put colonies in intense competition for pollen sources that may lack diversity, be poorly nourishing, or flower infrequently.”

Pollen is a bee’s source of protein as well as other nutrients: “The chief source of nutritional stress in colonies is inadequate access to pollen, which provides the essential protein, lipids, vitamins, and minerals that are required for larval development and adult function.”

It is a reason that sugar water, which is sometimes fed to bees in lean times, can be a poor substitute for real food—pollen and nectar.

Pollen shortages can impact a bee for life if they occur during the insect’s larval stage, the paper says.

“Pollen stress during larval development had far-reaching physical and behavioral effects on adult workers. Workers reared in pollen-stressed colonies were lighter and shorter lived than nestmates reared with adequate access to pollen,” the authors write.

The authors don’t say pollen shortages are the only problem for bees, but that the impacts of any other threats are magnified in the presences of nutritional deficiencies.

“We found that pollen stress during larval development had far-reaching negative effects on task performance by adults later in life. Critically, performance deficits extended to foraging and recruitment, which are the most important tasks that honey bees perform as provisioners for their colonies and as pollinators of human-cultivated crops,” they write.

Wild bees as well as managed hives have been severely impacted in the Islands by pests like the varroa mite and the small hive beetle. The health of bees is important, since so many Hawaiian crops are highly dependent on bees for pollination. They include avocado, lychee, longan, rambutan, starfruit, macadamia and guava. 

For more information on Hawaiian bees, check the University of Hawai`i Honeybee Project website

© Jan TenBruggencate 2015

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