Engineering pollinator phenotypes: Consequences of induced size variation on adult morphology and flight performance metrics in the solitary bee, Osmia lignaria

Body size is an important trait because it strongly correlates with morphology, performance, and fitness. In insects, the body size model argues that adult size is determined during the larval stage by the mechanisms regulating growth rate and the duration of growth. Though explicit links have been drawn between larval growth and adult size variation, few studies have examined how changes in size affect adult morphology and performance. In this study, we asked how altering larval growth impacts adult morphology and performance in the solitary bee pollinator, Osmia lignaria. We manipulated the duration of larval growth by the altering food provisions during larval development. This induced twice the variation in body size as is observed in natural populations with more than a 10-fold difference between smallest and largest adult bees. The impact of altered larval development on adult morphology was evaluated by examining allometric relationships between body size and head, thorax, and abdominal masses. We also examined how flight morphometrics varied with body size by evaluating wing loading and a flight power index. O. lignaria thoraces increased hypermetrically with body mass, but head and abdomens increased isometrically. Wing loading decreased with increasing adult mass, suggesting that flight was more energetically demanding in larger bees; however, the flight power index remained similar across different body sizes, indicating that increased thoracic investment offset challenges in flight for larger bees. These scaling relationships are consistent with the ecology of O. lignaria because reproductive performance is limited provisioning of nests rather than egg production.