Lost in the dark: why we still don't understand parasitoid decline and extinction

Abstract

Insect decline is a matter of serious concern to global biodiversity, yet most research is focused on a few well-studied groups. A significant portion of flying insects consists of the understudied parasitoid wasps, which are extremely high in species diversity and provide crucial ecosystem services, most notably regulation of host insect populations. For reasons that include small body size and scant diagnostic resources, these wasps are difficult to study at even the most basic level and are often referred to as “dark taxa.” In addition to the taxonomic impediment, the lack of accurate and comprehensive knowledge of host-parasitoid associations, the “ecological impediment,” is a critical barrier to monitoring parasitoid decline or extinction. In Germany, where flying insect biomass has decreased by more than 75% since the 1980s, the apparent disappearance of the giant platygastrid wasp, Isocybus grandis, exemplifies the manifold challenges of parasitoid conservation. The complexities of assessing the status of this species are aired as a case study. The taxonomic impediment, the ecological impediment, and their interrelationships are discussed in the context of lost species and dark extinctions.