Nesting cavity diameter has implications for management of the alfalfa leafcutting bee (Hymenoptera: Megachilidae)

Authors: RINEHART, JOSHUA - North Dakota State University; Grula, Courtney; Rinehart, Joe; BOWSHER, JULIA - North Dakota State University

Submitted to: Physiological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2023
Publication Date: 11/16/2023
Citation: Rinehart, J., Grula, C.C., Rinehart, J.P., Bowsher, J. 2023. Nesting cavity diameter has implications for management of the alfalfa leafcutting bee (Hymenoptera: Megachilidae). Physiological Entomology. https://doi.org/10.1093/jee/toad207.
DOI: https://doi.org/10.1093/jee/toad207

Interpretive Summary: Due to its importance in the production of alfalfa seed, the alfalfa leafcutting bee is the most intensely managed cavity nesting insect in the world. While much is known about the biology of this species, bee managers are constantly looking for methods to increase bee productivity and offspring yield. This study provides an in-depth report on the effects of nesting cavity size on the body size of this critically important pollinator. While bigger bees are produced in larger nesting cavities, such as the standard 7mm cavities used in commercial operations, we found that bees that came from 5 mm cavities have improved offspring yield and may also exhibit improved productivity in the field.

Technical Abstract: Body size influences performance in many bee species and is influenced by nest size. In the alfalfa leafcutting bee (Megachile rotundata), which is a commercially-managed, solitary cavity nesting bee, body size has low heritability and is strongly influenced by the size of the larval provision, temperature, and nest size. Commercial nesting boxes have nesting cavities that are seven millimeters in diameter. Our goal was to examine the effects that nest diameter has on M. rotundata body size by manipulating the size of cavities that are available for nesting. We provided bees with nesting cavities that vary in size from four to nine millimeters in 1-millimeter increments. We measured the following in the offspring: mass, wing area, intertegular span, sex, and diapause status. We also examined the reproductive output from the different nest cavity diameters. We found that while the 8-millimeter nests reared the largest bees, the four-millimeter nests reared the smallest bees. We also found that the 5-millimeter nests are the optimal cavity size as they yield larger quantities of offspring that are predominantly female, produced bees that that have similar body size morphometrics as bigger bees, and requires less resources for nest construction.