Cuticular microsculpturing: multispecies morphology of stridulatory structures in bark beetles of the genus Ips (Coleoptera: Curculionidae: Scolytinae).

Abstract

Stridulation is the only recognized mechanism for sound emission in Scolytinae, and at least half of its tribes manifest it. However, its morphology has been studied in almost 125 species, describing the location of the stridulatory apparatus. In a few groups, its morphological variation has been evaluated, mostly in characters of the striated surface of the pars stridens. Females of Ips DeGeer exhibit a stridulatory apparatus located on the pronotal apex and the vertex, which has been extensively documented in 18 of 37 species. However, the patterns of interspecific and intraspecific variation in pars stridens (on the vertex) and plectrum (on the pronotum) have not been thoroughly evaluated to test their taxonomic utility. Therefore, in this study, we proposed a set of 29 attributes for the pars stridens and plectrum to comprehensively quantify their morphological variation and evaluate their discriminatory power among eight species of Ips. These traits enable detailed characterization of the stridulatory apparatus, supporting their use as important diagnostic features. We also introduced a regionalization scheme for each structure to standardize comparisons across studies. Our results show that both structures covary, indicating phenotypic integration, and that the pars stridens offers stronger species-level discrimination than the plectrum.