Body and wing allometries reveal flight-fecundity tradeoff in response to larval provisioning in the blue orchard bee, Osmia lignaria

Authors: HELM, BRYAN - North Dakota State University; BALDWIN, MAXWELL - North Dakota State University; Rinehart, Joe; Yocum, George; GREENLEE, KENDRA - North Dakota State University; BOWSHER, JULIA - North Dakota State University

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: The size of an insect can greatly affect its performance, especially during the adult stage. Although this has been studied in many species, it has received less attention in pollinating insects. In this study, we investigated the effects of body size in an important alternative pollinator called the blue orchard bee by varying the amount of food that was available to them in their earlier life stages. Limiting the amount of food produced small bees, while adding more food resulted in bees that were over 10 times larger. First, we measured the size of the head, thorax, and abdomen of each bee, and found that the larger bees had smaller abdomens relative to the other body segments. Secondly, we measured wing sizes and discovered that small bees have larger wings with respect to their body size, and therefore have the potential to produce more lift for carrying loads. Hence, these results suggest that differences in body size may affect adult activity and ultimately pollinator performance.

Technical Abstract: Body size covaries with morphology, functional performance, and fitness. For insects, variation in adult size and morphology are determined by developmental variation during larval growth and metamorphosis. In this study, we asked how provision-dependent variation in adult size changes morphology in adult blue orchard bees, Osmia lignaria—with special attention given to traits that are critical for pollinator performance. O. lignaria larvae typically consume a finite quantity of food during the larval period, and adult size can be experimentally manipulated by limiting or augmenting larval provisions. This induces twice the variation in body size that is observed in natural populations with >10-fold difference between largest and smallest adult bees. We then examined the consequences of developmental variation on adult morphology in two ways. First, allometric relationships between major body regions (head, thorax, abdomen) and total body mass were measured to determine how relative growth of these structures changes under different provisioning conditions as larvae. Second, morphometrics that are critical for flight performance (wing area, wing loading, and extra flight power index) were quantified in the same individuals. Head and thorax mass had an hyperallometric relationship with size, indicating these parts become disproportionately large in adults when larvae are given copious provisions. However, abdominal mass and wing area increased hypoallometrically with body size. Thus, large adults had disproportionately lighter abdomens and smaller wing areas than smaller adults. Though both males and females followed these general patterns, allometric patterns were affected by sex. For flight metrics, small adults had reduced wing loading and an increased extra flight power index. These results suggest that developmental variation alters morphometric trait relationships in adult O. lignaria that may lead to functional differences in performance that play a critical role in pollinator performance.