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United States Department of Agriculture

Agricultural Research Service

Title: Do weather conditions correlate with findings in failed, provision-filled nest cells of Megachile rotundata (Hymenoptera:Megachilidae) in western North America?

Authors
item PITTS SINGER, THERESA
item JAMES, ROSALIND

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2008
Publication Date: June 20, 2008
Citation: Pitts Singer, T., James, R.R. 2008. Do weather conditions correlate with findings in failed, provision-filled nest cells of Megachile rotundata (Hymenoptera:Megachilidae) in western North America?. Journal of Economic Entomology. 101(3): 674-685

Interpretive Summary: Alfalfa leafcutting bees are excellent pollinators of alfalfa for seed production. Alfalfa leafcutting bees nest in pre-existing cavities, where female bees lays eggs on pollen-nectar provisions. In alfalfa seed production systems, nests are constructed in manufactured bee boards placed in field domiciles. For this study, nests containing bee offspring were collected from commercial boards in late summer from several northwestern U.S. states and from Manitoba, Canada. X-rays were used to identify “pollen balls” (i.e., cells in which the pollen-nectar provision remains but the egg or larva, if present, is not detectable on an x-ray). Most U.S. samples had higher proportions of pollen ball cells than Manitoba samples. Pollen ball cells were dissected to determine the moisture condition of the mass provision and true contents of the cell. Most pollen ball cells from Manitoba samples were overgrown with fungal hyphae. The frequency of fungus-filled cells in individual samples was positively correlated with cool, wet weather. In the U.S., most pollen ball cells had moist provisions, but many of them lacked young brood. Correlation analysis revealed that pollen ball cells occurred in greater proportions in fields with more hot days (above 27°C). Broodless pollen ball cells occurred in greater proportions under cool conditions, but pollen ball cells with dead eggs or small larvae occurred in greater proportions under hot conditions.

Technical Abstract: Alfalfa leafcutting bees, Megachile rotundata Fabricius, are excellent pollinators of alfalfa for seed production. Alfalfa leafcutting bee nests consist of a series of cells in a cavity. The female bee lays a single egg in each cell on a pollen-nectar provision. In alfalfa seed production systems, nests are constructed in manufactured bee boards placed in field domiciles. For this study, nests containing bee progeny were collected from commercial boards in late summer from several northwestern U.S. states and from Manitoba, Canada. X-radiography was used to identify “pollen balls” (i.e., cells in which the pollen-nectar provision remains but the egg or larva, if present, is not detectable on an x-radiograph). Most U.S. samples had higher proportions of pollen ball cells than Manitoba samples. Pollen ball cells were dissected to determine the moisture condition of the mass provision and true contents of the cell. Most pollen ball cells from Manitoba samples were overgrown with fungal hyphae. The frequency of fungus-filled cells in individual samples was positively correlated with cool, wet weather. In the U.S., most pollen ball cells had moist provisions, but many of them lacked young brood. Correlation analysis revealed that pollen ball cells occurred in greater proportions in fields with more hot days (above 27°C). Broodless pollen ball cells occurred in greater proportions under cool conditions, but pollen ball cells with dead eggs or small larvae occurred in greater proportions under hot conditions.

Last Modified: 9/29/2014
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