Integrative taxonomy based on morphometric and molecular data supports recognition of the three cryptic species within the Encyrtus sasakii complex (Hymenoptera, Encyrtidae)

Abstract

Morphometrics has established itself as one of the most powerful tools for species delimitation, particularly for morphologically-conserved groups of insects. An interesting example is the parasitoid Encyrtus sasakii Ishii (Hymenoptera: Chalcidoidea: Encyrtidae), which was recently subdivided into three cryptic species that are seemingly well-delimited with the available DNA data but nearly indistinguishable morphologically. Here, we performed linear morphometric analyses of the antenna as well as shape analyses of the ovipositor and hypopygium (the last two are key structures associated with host location and selection) to shed further light on the taxonomic status of the E. sasakii complex. Principal component analyses were carried out to visualize the amount and direction of shape variation in the ovipositor and hypopygium. Complementarily, we constructed phylogenetic trees using a Bayesian approach based on two markers (28S and COI). We found statistically-significant differences in the relative size of the funicle and of the two proximal claval antennomeres among the three species. Our analyses also indicated that the outer plates of the ovipositor show remarkable allometric changes and that both the stylus and shield of the ovipositor are relatively well conserved among species. We nonetheless found consistent interspecific differences in the shape of the 2nd outer plate of the ovipositor and hypopygium. Also, both our COI and combined trees recovered three strongly-supported major clades, each corresponding to one of the three cryptic species. We discuss that changes in the shape of the ovipositor may have played an important role in host shift and speciation within the E. sasakii complex. Even though the recent descriptions of both E. eulecaniumiae Wang & Zhang, 2016 and E. rhodococcusiae Wang & Zhang, 2016 appear not to fully satisfy the International Code of Zoological Nomenclature, a simple resolution for the sake of taxonomic stability is proposed herein.