Cutting the sap: First molecular phylogeny of twig‐girdler longhorn beetles (Coleoptera: Cerambycidae: Lamiinae: Onciderini) suggests shifts in host plant attack behaviours contributed to morphological evolution

Abstract Understanding how novel adaptive traits arise, evolve and impact other aspects of an organism's phenotype is a foundational question in evolutionary biology. We explore this by focusing on Onciderini (Coleoptera: Cerambycidae: Lamiinae), a tribe of longhorn beetles commonly referred to as twig girdlers because the females of some species girdle live trees to deposit their eggs. We reconstructed the first time‐calibrated phylogeny of the Onciderini, based on three genetic markers (cytochrome c oxidase subunit 1 ‘ cox1’ , Wingless ‘ Wg ’ and carbamoyl‐phosphate synthase domain of the CAD locus ‘ CPS’ ), and used morphometric data, employing multiple models of trait evolution and phylogenetic regressions, to assess whether girdling behaviour predicts head size or head size sexual dimorphism. Our results indicate that onciderines originated c. 49 million years ago ‘Ma’ (95% highest posterior densities ‘HPD’: 44.1–54.57 Ma) and consist of two major lineages, which we formalize as subtribes Hypsiomatina and Onciderina. Additionally, our analyses revealed several taxonomic inconsistencies within the tribe, which we rectify by proposing new synonymies, including Jamesia Jekel as a synonym of Hypselomus Perty, Cipriscola Dillon & Dillon of Hypsioma Audinet‐Serville and Psyllotoxus Thomson and Taricanus Thomson as a synonym of Oncideres Lacordaire, and a new combination for Periergates kenjii Nearns & Swift as Oncideres kenjii (Nearns & Swift) comb. nov . Using this new phylogenetic framework, we identified five independent unidirectional origins of girdling behaviour within the tribe. Overall, our results suggest that girdling influences head size evolution in Onciderini, as it is associated with an increase in both male and female head size of girdler species. Despite this, girdling and non‐girdling lineages do not consistently differ in head size sexual dimorphism. This study refines the classification of Onciderini and marks a significant step in understanding the evolutionary dynamics shaping the diversity of twig‐girdler beetles, a group with notable ecological and economic importance.