Parasitoid wasps are essential to our well-being and indeed to our long-term survival on a planet with rapidly dwindling resources. They provide numerous essential ecosystem services from insect population control (including those of pest species) to pollination. Just about every species of insect and arachnid in the world is attacked by a parasitoid wasp and in most cases by many more than one wasp species.
While some parasitoid species attack more than a single host species the vast majority are highly host-specific. This means that the order Hymenoptera (wasps, bees and ants) is by far the most diverse order of insects, given that there are on average 2-3 species of parasitoid wasps associated with every other insect species in the world (Forbes et al. 2008).
There are about 20 000 described species of African Hymenoptera, but I estimate that there are anything between 100 000 to half a million species of wasps still to describe from the region (van Noort, 2021). Effectively we know very little about our incredibly rich species diversity, and even less about their ecological interactions and the critical role they play in the functioning of our ecosystems upon which we are reliant for our own well-being.
Through their lifestyle strategy parasitoid wasps control other insect populations, without which we would experience massive population explosions of insects in plague proportions that would decimate our environment, including our agricultural and forestry industries. They are essential contributors to food security and to maintaining our environmental life support systems in a healthy state. As hyperparasitoids they also control population levels of other parasitoid wasps. In any given host insect food web scenario there can be numerous trophic levels, with a number of parasitoid species attacking the primary host as well as each other, with some species attacking parasitoid wasps that are attacking other parasitoid wasps developing on the same host insect!
They attack every developmental stage of the host from eggs to adults, with different species specialising on the various stages. The smallest insects in the world are parasitoid wasps in the family Mymaridae (commonly called Fairyfly wasps because of their feathery wings). At 0.15mm females of the fairyfly wasp Kikiki huna represent the smallest winged insect species (Huber & Beardsley, 2000), but wingless males of another fairyfly wasp Dicopomorpha echmepterygis are even smaller at 0.13mm (Mockford, 1997). The size of these minute, fully developed adult wasps is dictated and constrained by the limited food resources available for their larvae that develop inside tiny host insect eggs, eventually killing the host.
Through biocontrol programs, parasitoid wasps are deliberately and effectively used to control pest species of insects attacking our agroecosystems, or to control alien invasive insects and plants. Using parasitoids to control pests of crops reduces the need for insecticide use and mitigates the resultant knock-on effect on health of the broader environment. Invasive species have a major negative impact on our indigenous ecosystems, many of which are kept under control by parasitoid wasps (van Noort et al submitted). Exotic invasive waterweeds are a major issue clogging our water systems and impacting on their efficient functioning, and are often controlled by introduced plant feeding insects, but parasitoid wasps also attack biocontrol agents, and hence may have a potential negative impact (Kraus et al. 2019; van Noort et al, 2021). Other parasitoid wasps are invasive pests themselves, or may potentially impact on conservation of critically endangered host species (Armstrong et al 2020), so it is very important to understand the specific role these parasitoids are playing in any given host interaction.
Although most feeding occurs in the larval stage, adult parasitoid wasps also need to imbibe nutrients, which they often obtain from body fluids exuding from puncture wounds on the host insect during the process of egg laying, but they also feed on nectar for their energy requirements, and in the process perform critical pollination services. Some of these pollinator/plant interactions are highly specialised. The most well-known is the classic example of an obligate mutualism that exists between fig wasps and their host fig trees, neither of which can survive without the other. Fig trees are completely reliant on tiny fig wasps for pollination, and in turn the wasps can breed nowhere else except inside figs. Fig trees are keystone species in tropical ecosystems with many other animals relying on the food resources provided by Ficus species for their own survival.
Loss of the pollinating wasps would have catastrophic cascading effects on ecosystem functioning, and impact of habitat transformation on gene flow within populations of this mutualism may have ramifications for conservation of our ecosystems (Deng et al. 2020). With rapidly increasing rates of human induced environmental destruction, and habitat transformation due to climate change, implementation of ongoing initiatives to survey our diverse ecosystems is a matter of priority. The vast majority of African vegetation types are under-sampled and every inventory survey produces hundreds to thousands of undescribed species of wasps. The resulting samples, safe-guarded in South African museum collections, are necessary to provide essential baseline data for assessing rates of spatial and temporal change in our invertebrate species richness and abundance. Rigorous, quantified, continuous invertebrate inventory surveys conducted over the last 30 years by Simon van Noort have resulted in an estimated 10 million specimens that are housed in the Iziko South African Museum entomology collection.
Given that we currently have very limited baseline data on South Africa’s invertebrate species richness available to assess the local extent of the insect Armageddon the globe is experiencing, this resource is a goldmine of biodiversity data that when mobilised will inform rates of decline in our insect populations. There is no doubt that in South Africa we are also rapidly losing much of our biodiversity heritage, but we have no idea of the rate that this is happening at. With leverage of appropriate resources to mobilise data conserved in our natural history collections, and via research conducted by world specialists on South Africa’s rich fauna, we will be in a better position to make these critical assessments. We are losing species to extinction faster than we can discover and describe them. It is now more important than it has ever been to mobilise taxonomic resources and leverage appropriate funding to focus our effort on discovery, description and documentation of our wealth of unknown species. In the process mobilising the associated specimen metadata and escalating it up through the value chain for the benefit of science and society.
Extremely sobering to realise that the vast majority of unknown insect species are in fact parasitoid wasps! Explore the National Science Collections Facility Webinar Series showcasing the value of museum collections for further information and details of why parasitoid wasps are so important.