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

Abstract

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 categorized larval diet breadth based on the phylogenetic structure of utilized 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 occur exclusively in the early season. Furthermore, the adult body size is significantly smaller in species that overwinter in the pupal stage compared to those that overwinter as eggs or caterpillars. In summary, our results indicate that the ecological niche of holometabolous insect herbivores is strongly interrelated with body size at maturity.

Macroecological patterns in European butterflies unveil strong interrelations between larval diet breadth, latitudinal range size and voltinism

“…Only about a quarter of the analysed butterfly species is strictly monophagous on plant genus level. In a similar study on European geometrid moths, the fraction of monophages turned out to be distinctly higher with 40% of the species (Seifert et al 2023). Hence, the rather low fraction of monophagous butterflies might be surprising at first glance, given that this insect group is frequently taken as a prominent case of predominantly narrow food specialists.…”

“…However, non‐monophagous butterflies are on average still more restricted in their phylogenetic diet breadth than non‐monophagous geometrids (cf. Seifert et al 2023), which illustrates that butterflies are indeed overall more strongly constrained to specific plant lineages than looper moths. The slightly lower observed incidence of monophagy on plant genus level among butterflies probably also reflects the more comprehensive recording, since observations of ‘exceptional' host plant affiliations are more likely to be publicised in butterflies than for other lepidopteran groups.…”

“…In terms of diet breadth, however, lycaenid species show strong interspecific variation, ranging from monophagous to highly polyphagous taxa. Overall, it seems increasingly likely that the body size – diet breadth relationship is determined by additional characteristics of the respective herbivore group under study, such as feeding guild (Novotny and Basset 1999) or host plant growth form (Seifert et al 2023). Further comparative studies, preferably including various groups of insect herbivores, are needed to test for the validity of this assumption.…”

“…Despite the strong support that the ‘body size – diet breadth relationship' received in a number of studies (Loder et al 1998, Brändle et al 2000, Davis et al 2013), it remains questionable whether it is of as broad generality as previously thought (cf. Novotny and Basset 1999, Seifert et al 2023). However, since insect body size was found to positively relate with dispersal ability (Sekar 2012, Stevens et al 2012), understanding its relationship with diet breadth is crucial to evaluate whether generalists may have a higher capacity for range shifts than specialists.…”

“…It is further likely that body size, range size, and voltinism are to some extent linked and thus cannot evolve completely independent from another. In Lepidoptera, for instance, it was shown that body size is positively related with range size (Brändle et al 2002) and seasonality (Ribeiro and Freitas 2011, Seifert et al 2023), while the latter, in turn, might increase with range size (Brändle et al 2002). Hence, possible indirect relationships between all these characteristics must be considered when investigating their associations with diet breadth.…”