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.