Temporal and spatial variations in the parasitoid complex of the horse chestnut leafminer during its invasion of Europe

The enemy release hypothesis posits that the initial success of invasive species depends on the scarcity and poor adaptation of native natural enemies such as predators and parasitoids. As for parasitoids, invading hosts are first attacked at low rates by a species-poor complex of mainly generalist species. Over the years, however, parasitoid richness may increase either because the invading host continuously encounters new parasitoid species during its spread (geographic spread-hypothesis) or because local parasitoids need different periods of time to adapt to the novel host (adjustment-hypothesis). Both scenarios should result in a continuous increase of parasitoid richness over time. In this study, we reconstructed the development of the hymenopteran parasitoid complex of the invasive leafminer Cameraria ohridella (Lepidoptera, Gracillariidae). Our results show that the overall parasitism rate increases as a function of host residence time as well as geographic and climatic factors, altogether reflecting the historic spread of C. ohridella. The same variables also explain the individual parasitism rates of several species in the parasitoid complex, but fail to explain the abundance of others. Evidence supporting the “geographic spread-hypothesis” was found in the parasitism pattern of Cirrospilus talitzkii (Hymenoptera, Eulophidae), while that of Pediobius saulius, another eulophid, indicated an increase of parasitism rates by behavioral, phenological or biological adjustments. Compared to fully integrated host-parasitoid associations, however, parasitism rates of C. ohridella are still very low. In addition, the parasitoid complex lacks specialists, provided that the species determined are valid and not complexes of cryptic (and presumably more specialized) species. Probably, the adjustment of specialist parasitoids requires more than a few decades, particularly to invaders which establish in ecological niches free of native hosts, thus eliminating any possibility of recruitment of pre-adapted parasitoids

Morphological and Molecular Identification Protocols for Bactrocera dorsalis: A Joint Validation Study

Bactrocera dorsalis is considered among the most destructive and economically important invasive fruit flies worldwide. Native to Southeast Asia, in just a few years, it has spread almost throughout all of sub-Saharan Africa, causing fruit loss in several commercially grown crops. In Europe, it is frequently intercepted as larva on imported fruits during phytosanitary inspections. In recent years, adult specimens have been caught in traps in Austria, Italy, and France, increasing the level of attention to this species. Rapid and unambiguous identification by European plant health laboratories is important to effectively prevent its introduction and establishment in Europe. The harmonized use of validated diagnostic protocols is essential. However, in entomology, unlike other disciplines, diagnostic protocols often lack validation data to support their suitability as adequate identification tools. In this study, tests from two international diagnostic protocols for the identification of B. dorsalis underwent a thorough validation process to assess their performance characteristics (analytical and diagnostic sensitivity, specificity, accuracy, repeatability, and reproducibility). A novel process of a joint validation of morphological and molecular identification protocols is reported. The novelty of this approach arises from the fact that morphological and molecular tests are validated in the same study, based on the same panel of samples, also allowing a two-way control on the assigned values of samples. Potential critical issues that could represent weaknesses of the protocols are also discussed in detail. [Graphic: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license