Cell position during larval development affects postdiapause development in Megachile rotundata (Hymenoptera: Megachilidae)

Authors: Yocum, George; Rinehart, Joseph - Joe; Kemp, William - Bill

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2014
Publication Date: 8/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59552
Citation: Yocum, G.D., Rinehart, J.P., Kemp, W.P. 2014. Cell position during larval development affects postdiapause development in Megachile rotundata (Hymenoptera: Megachilidae). Environmental Entomology. 43(4):1045-1052.

Interpretive Summary: The alfalfa leafcutting bee Megachile rotundata is the primary pollinator of alfalfa in the northwestern United States and western Canada and provides pollination services for onion, carrot, hybrid canola, various legumes and other specialty crops. Female M. rotundata nest in cavities either naturally occurring or artificial nesting blocks, where they construct a linear series of brood cells. A female can construct and provision 1 to 2 brood cells a day, so the age difference between the first and last larvae may be 4 to 11 days. Because of the physical layout of the nest and the age differences of the larvae within the nest, larvae will experience differences in temperature and oxygen concentrations during development. These two interacting factors, along with other maternal inputs, could affect the resulting physiological characteristics of the nest mates and thereby affect the bees ability to reproduce and pollinate crops. To further our understanding of nest physiology, key physiological traits were examined in relationship to cell position within the nest. Eighty two percent of the females were located within the first three cells, those furthest from the nest entrance. For those individuals developing in cells located in the deepest half of the nest, the sex of the previous bee had a significant effect on the gender of the following nest mate. Removing the prepupae from the nest and rearing them under identical conditions demonstrated that position within the nest during larval development had a significant effect on pupal to adult developmental rates, with males whose larval development occurred deeper in the nest developing more slowly than those toward the entrance. No positional effect on pupal to adult developmental rates was noted for the females. The quantity and quality of M. rotundata under a managed system is the sum total of many interacting environmental and maternal factors. Developing a more thorough understanding of these interactions is essential for the development of sustainable management practices for M. rotundata.

Technical Abstract: Megachile rotundata (F.) (Hymenoptera: Megachilidae) is the primary pollinator of alfalfa in the northwestern United States and western Canada and provides pollination services for onion, carrot, hybrid canola, various legumes and other specialty crops. Female M. rotundata are gregarious, nest in cavities either naturally occurring or artificial nesting blocks, where they construct a linear series of brood cells. Because of the physical layout of the nest, the age of the larvae within the nest and the microenvironment the individual larvae will experience will vary. These two interacting factors along with other maternal inputs affect the resulting phenotypes of the nest mates. To further our understanding of nest physiology, key physiological traits were examined in relationship to cell position within the nest. Eighty two percent of the females were located within the first three cells, those furthest from the nest entrance. For those individuals developing in cells located in the deepest half of the nest, the sex of the previous bee had a significant effect on the gender of the following nest mate. Removing the prepupae from the nest and rearing them under identical conditions demonstrated that position within the nest during larval development had a significant effect on the post-diapause developmental rates, with males whose larval development occurred deeper in the nest developing more slowly than those toward the entrance. No positional effect on post-diapause developmental rates was noted for the females. The quantity and quality of M. rotundata under a managed system is the sum total of many interacting factors. Understanding the range of M. rotundata phenotypic plasticity is therefore essential for sustainable management practices.