Invasive host caught up with a native parasitoid: field data reveal high parasitism of Harmonia axyridis by Dinocampus coccinellae in Central Europe

Abstract

The harlequin ladybird, Harmonia axyridis, is considered to be one of the most invasive insect species worldwide. Its invasion success and extreme speed of range expansion has been partially attributed to weak control of its populations by natural enemies. Previously published data on emergence rates of the hymenopteran parasitoid Dinocampus coccinellae support the enemy release hypothesis: H. axyridis has been consistently less successfully parasitized compared to native ladybird species. In this study, we show that since 2016, i.e., 10 years after its arrival in Central Europe, several populations of H. axyridis in the Czech Republic have a very high prevalence of D. coccinellae parasitism. D. coccinellae emerged from 46% of H. axyridis individuals in the most parasitized population. Moreover, H. axyridis was more parasitized than the native Coccinella septempunctata in seven of nine investigated co-occurring populations. The meta-analytically pooled estimate of D. coccinellae emergence rate from H. axyridis across the Czech populations (this study) is thirteen times higher than the pooled estimate for invasive populations of this beetle elsewhere (historical data up to 2016). We hypothesize that some Central European populations of D. coccinellae have evolved to overcome the immune system of H. axyridis, which was previously thought to be responsible for the high larval mortality of D. coccinellae. As parasitism rates are highly variable in time and space, we encourage future research investigating the determinants of parasitoid prevalence in H. axyridis and other large ladybird species on a continental scale.