A dramatic decline in bee populations at fruit farms in New Jersey and Pennsylvania has led scientists wonder whether these changes are just natural fluctuations, or warnings regarding significant future threats to the global food supply. Since the study has been conducted over an eight-year period (2005 to 2012), it is not possible to clearly conclude whether this decline represents a true drop in bee numbers, or only a normal variation over a larger cycle.
“This study is important because it is one of the first to assess trends in wild bee abundance in an agricultural system, where bees are providing an economically important ecosystem service,” said lead author Andrew Aldercotte, a doctoral candidate in Ecology and Evolution at Rutgers University. “Despite widespread recognition of the need for long-term monitoring of pollinator abundances and pollination service provision, such studies are exceedingly rare.”
“We saw two things come out,” Aldercotte added. “One was that the rate of visitation by bees was really low for the last two years of the study. But we also saw that the numbers bounced around a lot from year to year.”
The scientists analyzed data collected at 19 commercial farms in central New Jersey and eastern Pennsylvania during peak bloom periods from 2005 to 2012, focusing on pollination visits by 73 species of bees (including wild bees, bumblebees, and honey bees) to the flowers of watermelon plants. The analysis reveled that pollination of watermelon flowers by wild bees and bumblebees declined by more than half during that period, while the population of honey bees – which are not native to those regions and are managed in hives by farmers – remained largely stable.
“Data collectors watched flowers for periods of 45 seconds and wrote down every bee visit they observed and then moved on and observed another flower for a period of 45 seconds,” Aldercotte said. “And they kept doing that throughout the day.”
While in New Jersey the bee populations were still sufficient to pollinate crops, studies of other crops in different parts of the country show that insufficient pollination often reduce crop production. Further longitudinal studies are needed to clarify whether the population of bees overall is declining or if these drop in numbers reflect a natural variation over time.
The study is published in the journal Insect Conservation and Diversity.