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United States Department of Agriculture

Agricultural Research Service

Title: Examination of "pollen Balls" in the Nests of the Alfalfa Leafcutting Bee, Megachile Rotundata

Author
item PITTS SINGER, THERESA

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 2003
Publication Date: May 7, 2004
Citation: Pitts Singer, T. 2004. Examination of "Pollen Balls" in the nests of the alfalfa leafcutting bee, Megachile rotundata. Journal of Apicultural Research. 43(2):40-46.

Interpretive Summary: Nests of Megachile rotundata, the alfalfa leafcutting bee, were removed from alfalfa fields in the early fall. Bee cells were studied using x-rays. Many (20-50%) of the cells contained pollen balls - provisioned bee cells that lack healthy eggs or larvae. Most of the provisions were moist, with ¼ of the cells being very dry. Many pollen balls contained dead eggs or larvae, and a moderate proportion of them contained a mass provision in which no egg had been laid. Other cells contained incomplete or no provisions along with older dead larvae, beetle larvae and their feces, and saprophytic fungi (including molds). Our findings show that x-ray analysis does not always reveal the true content of pollen ball cells. These results help to direct future studies into the cause of high pollen ball production, which signifies high bee mortality. Also, the term "pollen ball" is imprecise for describing of the diverse array of contents found in these non-productive bee cells.

Technical Abstract: Nests of Megachile rotundata, the alfalfa leafcutting bee, were removed from alfalfa fields in the early fall. X-radiography was used to analyze nests and revealed that 20-50% of the cells contained pollen balls ¿ provisioned bee cells that lack healthy eggs or larvae. Dissection of pollen balls showed that most were at least somewhat moist, with 25% being very dry. Many pollen balls contained collapsed eggs or first instars, and a moderate proportion of them contained a mass provision in which no egg had been laid. Other cells contained incomplete or no provisions along with older dead larvae, beetle larvae and their feces, and saprophytic fungi (including molds). Our findings indicate that x-ray analysis is inadequate for determining the true content of pollen ball cells. These results help to direct future studies into the cause of high pollen ball production by alfalfa leafcutting bees. Also, the term "pollen ball" is imprecise for describing of the diverse array of contents found in these non-productive bee cells.

Last Modified: 9/10/2014
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