A critique of common methods for comparing the scaling of vertical force production in flying insects

Abstract

Maximum vertical force production (Fvert) is an integral measure of flight performance that generally scales with size. Numerous methods of measuring Fvert and body size exist, but few studies have compared how these methods affect the conclusions of scaling analyses. We compared two common techniques for measuring Fvert in bumblebees (Bombus impatiens) and mason bees (Osmia lignaria), and examined Fvert scaling using five size metrics. Fvert results were similar with incremental or asymptotic load-lifting, but scaling analyses were sensitive to the size metric used. Analyses based on some size metrics indicated similar scaling exponents and coefficients between species, whereas other metrics indicated different coefficients. Furthermore, Fvert showed isometry with body lengths and fed and starved masses, but negative allometry with dry mass. We conclude that Fvert can be measured using either incremental or asymptotic loading but choosing a size metric for scaling studies requires careful consideration.