An evaluation of common methods for comparing the scaling of vertical force production in flying insects

Maximum vertical force production (F_vert) is an integral measure of flight performance that generally scales with size. Numerous methods of measuring F_vert and body size are accessible to entomologists, but we do not know whether method selection affects inter- and intraspecific comparisons of F_vert-size scaling. We compared two common techniques for measuring F_vert in bumblebees (Bombus impatiens) and mason bees (Osmia lignaria), and examined F_vert scaling using five size metrics. F_vert 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 coefficients that differed by up to 18%. Furthermore, F_vert showed isometry with body lengths and fed and starved masses, but negative allometry with dry mass. We conclude that F_vert can be measured using either incremental or asymptotic loading but choosing a size metric for scaling studies requires careful consideration.