UA Researcher’s Paper Looks for Leads in Bee Population Decline

TUSCALOOSA, Ala. — Domesticating bees for agricultural pollination may present a greater risk for transmitting the kinds of pathogens that are threatening wild bumble bee populations as a whole, a paper co-written by a University of Alabama biologist says.

The paper, “A test of the invasive pathogen hypothesis of bumble bee decline in North America,” appears in April in the Proceedings of the National Academy of Sciences. Dr. Jeffrey Lozier, UA assistant professor of biological sciences at UA, is a co-author, along with Drs. Sydney A. Cameron (lead author), Haw Chuan Lim, Michelle A. Duennes and Robbin W. Thorp.

Lozier and his colleagues used genetic markers to detect species-threatening fungal pathogen Nosema bombi in thousands of specimens from declining bumble bee (Bombus) species in U.S. museums from 1980 onward.

“In previous studies we’d documented declines in some bumble bee species, but causes were unclear,” Lozier said. “We had observed positive correlations between decline status of in the United States and N. bombi prevalence, but wanted to get a better idea of how the frequency of N. bombi has changed and possibly determine its geographic origins.”

They found that although Nosema was present in wild-bee populations in the earliest samples, the frequency of DNA detection increased in the early 1990s, around the beginning of bumble bee domestication for agricultural pollinations in North America and just before widespread observations of species decline.

The scientists report that they found evidence of N. bombi in U.S. bee populations before 1992. Earlier theories had suggested that N. bombi was introduced to U.S. bee populations through contact with European bees in the early 1990s.

“We used DNA sequencing to test whether a novel Nosema strain may have been introduced,” Lozier said. “The genetic markers showed that the Nosema strain found in declining United States bumble bees was here before commercial colony trade and observed species declines. Although the same DNA sequences are also found in Europe, the low genetic diversity we found makes it hard to determine whether a new strain was introduced. It is possible a widespread strain simply increased in frequency in North America.

“Regardless of geographic origins, the timing of Nosema bombi outbreaks in commercial Bombus, our observed increases in wild populations, and previous evidence for a correlation between Nosema infections and population declines adds to the increasing concern of pathogen transmission associated with domestication of some U. S. bumble bee species,” Lozier said.

The study addresses a growing problem: “Wild bumble-bee populations are declining throughout the world, but at the same time certain species are being moved around outside their natural ranges for pollination purposes, potentially bringing parasites along for the ride,” Lozier said.

Lozier and his colleagues suggest that with the growth of using domesticated colonies of bees to pollinate crops, the domesticated bees are interacting with their wild brethren, thus spreading these pathogens more quickly.

The researchers are attempting to find the causes of the decline; Nosema is a leading culprit, “but there are certainly many factors involved, and more work needs to be done, but developing native populations for pollination services is probably a sensible goal,” Lozier said.

The UA department of biological sciences is part of the College of Arts and Sciences, UA’s largest division and the largest liberal arts college in the state. Students from the College have won numerous national awards including Rhodes, Goldwater and Truman scholarships.