Evolutionary history suggests nymphal origin of antennal expansions in adult leaf‐footed bugs

Abstract Insect antennae morphology is highly conserved in many insect families, yet in some clades, elaborations of antennae form are more common. Leaf‐footed bugs (Hemiptera: Coreidae) are one case where there is considerable variation in antennal morphology. Antennae can be rectilinear, with cylindrical antennomeres, or have laterally flattened expansions that differ in which antennomeres they occur. Strikingly, such variation is also found across development, where nymphs and adults can also display different antennal shapes. Thus, Coreidae presents a unique opportunity to study how much shared ancestry and development influence antennal variation. We characterized the antennal expansion across a recent Coreidae phylogeny using research‐grade iNaturalist photos and primary taxonomic descriptions of adults (species) and nymphs (genus). We then performed ancestral reconstructions to estimate how many transitions between antennal states occurred across the phylogeny and compared these patterns between adults and nymphs. We found that adult antennal expansions are rare and restricted to Coreinae. The reconstructed history is consistent with repeated transitions to expanded adult antennae across Coreinae, with expansion most commonly confined to the third antennomere and concentrated in a few genera. In contrast, nymphal data reveal that antennal expansions are more widespread and often occur in genera whose adults lack expansions, suggesting that conspicuous antennal morphologies can be developmentally transient and frequently lost before adulthood. Together, our results indicate that adult antennal expansion is associated with nymphal expansion in the sampled genera and may reflect repeated retention or prolongation of a morphology expressed during development. Additionally, we provide a comparative framework for future work on the functional and developmental bases of exaggerated antennal forms.