How do host-plant use and seasonal life cycle relate to insect body size: A case study on European geometrid moths (Lepidoptera: Geometridae)

We used European geometrid moths (> 630 species) as a model group to investigate how life history traits linked to larval host plant use (i.e., diet breadth and host-plant growth form) and seasonal life cycle (i.e., voltinism, overwintering stage, and caterpillar phenology) are related to adult body size in holometabolous insect herbivores. To do so, we applied phylogenetic comparative methods to account for shared evolutionary history among herbivore species. We further categorised larval diet breadth based on the phylogenetic structure of utilised host plant genera. Our results indicate that species associated with woody plants are, on average, larger than herb feeders and increase in size with increasing diet breadth. Obligatorily univoltine species are larger than multivoltine species, and attain larger sizes when their larvae are restricted to the early season. Furthermore, adult body size is significantly smaller in species that overwinter in the pupal stage compared to those that overwinter as egg or caterpillar. In summary, our results indicate that the ecological niche of an holometabolous insect herbivore is strongly interrelated with its size at maturity.

Methods
We compiled information on overwintering stage (546 species) and caterpillar phenology (138 species) for European geometrid moths (Lepidoptera: Geometridae). Information was compiled based on available literature and reliable online sources.