ARS | Publication request: EMERGENCE SUCCESS AND SEX RATIO OF COMMERCIAL ALFALFA LEAFCUTTING BEES, FROM THE UNITED STATES AND CANADA

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2005
Publication Date: December 8, 2005
Citation: Pitts Singer, T., James, R.R. 2005. Emergence success and sex ratio of commercial alfalfa leafcutting bees, from the United States and Canada. Journal of Economic Entomology. 98(6):1785-1790.

Interpretive Summary: Samples of overwintering alfalfa leafcutting bee cells were collected from seven northwestern states and from Canada. Cells were x-rayed and scored as healthy, dead, or parasitized. Cells containing healthy prepupae were incubated in the laboratory, and the daily emergence of adults was recorded by the number of males and number of females. Cells from which no adult emerged were dissected to determine when the bee died (as a prepupa, pupa or adult) and the sex of any dead pupae or adults. Bee populations that had been incubated in commercial settings and released in alfalfa fields also were evaluated to determine adult emergence success. Results showed that the proportion of live bees in nest boards from the United States was far less than the proportion of live bees in nest boards from Canada, and nest boards from both countries contained fewer live bees than bee populations stored as loose cells. For loose cells reared in the laboratory, more adults survived in the Canadian samples than those from the U.S., and there were more males in the Canadian bee samples than in the U.S. samples. The timing of emergence was not different between the two counties. Fewer bees survived in the commercial setting than in controlled conditions of the laboratory, and more bees survived the incubation process if they were from a Canadian source. Most bees that did not survive during incubation were still prepupae. If bees died as adults, males were not more likely than females to have died. This study supports the common-held belief that alfalfa leafcutting bees raised in Canada and then sold to the U.S. are healthier than those raised in the U.S.

Technical Abstract: Samples of overwintering alfalfa leafcutting bee cells were collected from seven northwestern states and from Canada. Cells were x-radiographed and scored as healthy, dead, or parasitized. Cells containing healthy prepupae were incubated in the laboratory, and the subsequent daily emergence of adults was recorded by sex. Cells from which no adult emerged were dissected to determine the stage bee mortality and the sex of dead pupae or adults. Bee populations that had been incubated in commercial settings and released in alfalfa fields also were evaluated to determine adult emergence success. Results showed that the proportion of live bees in nest boards from the United States was far less than the proportion of live bees in nest boards from Canada, and nest boards from both countries contained fewer live bees than bee populations stored as loose cells. For loose cells reared in the laboratory, there were statistical differences between the U. S. and Canada bee cell samples in adult survival and sex ratios, but not in emergence onset and duration. It was also found that fewer bees survived in the commercial setting than in controlled conditions of the laboratory. Significantly more bees survived the incubation process if they were from a Canadian source, and if they were incubated under laboratory conditions. There was no difference in the likelihood of bee survival during incubation according to sex, but prepupal mortality was higher than pupal or adult mortality. This study supports the common-held belief that alfalfa leafcutting bees raised in Canada and then sold to the U.S. are healthier than those raised in the U.S.