Body size allometry impacts flight-related morphology and metabolic rates in the solitary bee Megachile rotundata

Authors: GRULA, COURTNEY - North Dakota State University; Rinehart, Joe; GREENLEE, KENDRA - North Dakota State University; BOWSHER, JULIA - North Dakota State University

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2021
Publication Date: 7/2/2021
Citation: Grula, C.C., Rinehart, J.P., Greenlee, K.J., Bowsher, J.H. 2021. Body size allometry impacts flight-related morphology and metabolic rates in the solitary bee Megachile rotundata. Journal of Insect Physiology. 133. Article 104275. https://doi.org/10.1016/j.jinsphys.2021.104275.
DOI: https://doi.org/10.1016/j.jinsphys.2021.104275

Interpretive Summary: The body size of an adult bee affects many aspects of its life, including how far they can forage and how efficiently they can pollinate. The goal of this study was to determine how body size impacts flight performance in the alfalfa leafcutting bee, a solitary bee used as an alternative pollinator. By restricting or providing excess food during the larval stages, we produced adults with a range of body sizes. This allowed us to study how body size affected metabolic rate during flight (by measuring carbon dioxide emissions) and various mechanical aspects of flight, including wing beat frequency, how heavily the wings were loaded, and how much extra power was available to carry loads. We found that when measured per insect, larger bees used more energy during flight, but when measured per gram of insect, there were no metabolic differences between large and small bees. Also, while wing beat frequency was not affected by body size, larger bees showed increased wing loading and a decrease in excess power. Taken together, these observations suggest that in this species, a smaller body size is advantageous during flight because they have more power available during flight with no apparent metabolic cost.

Technical Abstract: Body size is related to many aspects of a bee’s life history, including foraging distance and pollination efficiency. In solitary bees, adult body size is determined during the larval stage. Previous work has shown that manipulating the amount of larval diet produces intraspecific differences in adult body size. The goal of this study was to determine how body size impacts flight performance. By restricting or providing excess food, we produced a range of body sizes, which allowed us to test the impact of body size on the power required for flight and amount of energy produced, as measured indirectly through CO2 emission. The power required during flight was predicted via the flight biomechanical formulas wing loading and excess power index. We found larger bees had higher absolute metabolic rates at rest and during flight, but smaller bees had higher mass-specific metabolic rates at rest. During flight, bees did not have size-related differences in mass-specific metabolic rate. Smaller bees had more power available during flight as demonstrated by flight biomechanical formulas. Smaller body size was advantageous because of a reduced power requirement for flight at no metabolic cost.