The geographic scope of host use by the ladybeetle parasitoid Dinocampus coccinellae

Dinocampus coccinellae (Hymenoptera: Braconidae) can parasitize over 50 species of ladybeetles (Coleoptera: Coccinellidae), including the invasive Harmonia axyridis. The biological invasion success of H. axyridis has been in part attributed to weak control by natural enemies (Enemy Release Hypothesis). The main aim of this study was to examine (i) the intraspecific variation in field parasitism of D. coccinellae attacking H. axyridis populations in its native (Asia) and invasive ranges (North and South America and Europe), and (ii) the interspecific variation in field parasitism of D. coccinellae attacking the invasive H. axyridis and native hosts in the US (Coleomegilla maculata), Chile (Eriopis chilensis), and Italy (Coccinella septempunctata). We also characterized the genetic differentiation of D. coccinellae populations (from different host species and geographical areas) to infer its putative origin. Parasitism of D. coccinellae on invasive H. axyridis and native hosts were remarkably similar at 4-7%, suggesting a low level of resistance, not supporting the enemy release hypothesis. However, parasitism of H. axyridis was much lower in its native than in the invaded areas studied, indicating that under certain field conditions, it may contribute to the control of invasive populations of H. axyridis. Genetic relationships showed widespread D. coccinellae haplotypes with no host-associated genetic structure, consistent with a generalist parasitoid. Genetic relationships of the haplotypes also suggest a complex introduction scenario, with multiple introductions into America and an inferred European origin for D. coccinellae.

Automated summary

This study examined the variation in parasitism of D. coccinellae on H. axyridis populations in different regions and hosts, and inferred its putative origin. The results showed that parasitism rates of D. coccinellae on invasive H. axyridis and native hosts were remarkably similar, not supporting the enemy release hypothesis. However, parasitism rates of H. axyridis were much lower in its native range, indicating a potential contribution to the control of invasive populations. Genetic relationships analysis revealed widespread haplotypes of D. coccinellae with no host-associated genetic structure.