Predicting insect body masses based on linear measurements: a phylogenetic case study on geometrid moths

Dry body mass (DBM) is perhaps the most biologically informative variable describing body size in invertebrates. Unfortunately, obtaining species-specific indices of DBM is problematic because body mass inevitably changes during the course of the life of an individual. Here, we present a phylogenetically informed analysis of allometric relationships between body size and various linear measurements in the moth family Geometridae, which relies on DBM recorded at a fixed time point of adult life. We demonstrate that all measurements of wing size predict DBM with reasonable accuracy, with the distance between the most distal ends of the two forewings in traditionally mounted moths showing the best performance. Abdomen width provides independent morphometric information and can be used as a proxy of body plan, i.e. a measurement of shape that is not dependent on size. Incorporating abdomen width into the regression models considerably increases their predictive ability. We also show that the allometric relationships are reasonably consistent between the two sexes, between monophyletic clades of Geometridae and between the two geographical regions involved in the study (northern Europe and equatorial Africa). The derived equations thus appear to be general enough to be applied in various studies, from comparative phylogenetic analyses to applied projects monitoring insect biomass.