Combining molecular and morphological approaches to differentiate the pest Costelytra zealandica (White) (Coleoptera: Scarabeidae: Melolonthinae) from the non-pest Costelytra brunneum (Broun) at the larval stage

Abstract

The frequently strong morphological similarities that exist between the larvae of congeneric scarab beetles are likely to lead to misidentification of field-collected specimens of sympatric species. This is the case for the New Zealand endemic pasture pest Costelytra zealandica (White, 1846) (Scarabaeidae: Melolonthinae) and the closely related non-pest species C. brunneum (Broun, 1880), where a taxonomic key is only available for C. zealandica and does not allow the distinction between the two species. Mistaken identification and sampling of such fundamentally different organisms during ecological and/or behavioural studies could lead to invalid interpretations and misinformed decisions in the establishment of pest control programs. Molecular-based species identification is nowadays recognised as an effective way to identify cryptic species using barcoding regions of the genome. In this paper, we coupled this genetic approach with traditional scarab taxonomy (i.e. morphology of the raster, mandibles, labrum and epipharynx) to detect the morphological characteristics that allow for a rapid and accurate differentiation between the final instar of C. zealandica and C. brunneum larvae. We found out that as few as three characters allowed an accurate identification and that the morphology of the septula of the raster itself was enough to assist with a preliminary differentiation of the two species in the field.