Key points
- Parasitoid wasps develop in the eggs and bodies of their insect hosts, eating them from the inside out.
- In nature, they regulate insect numbers and can be used for biocontrol.
- In fiction, they are much more alien.
Dr Ian Naumann, retired fellow and wasp expert at our Australian National Insect Collection (ANIC), is in his office looking down a microscope at a tray of tiny wasps. They are so small they look like tea leaves rescued from the bottom of a cup.
Lights, camera, alien wasp
Legend has it the alien of the movie franchise was inspired by parasitoid wasps. The scene in which an alien bursts from the body of its human host plays on repeat in the world of parasitoid wasps and their insect or spider hosts.
There are thousands of species of parasitoid wasps. These range from tiny wasps that consume the eggs of other insects, to large wasps that paralyse spiders with stings that are painful to humans.
The wasps Ian is currently studying belong to the genus Anastatus in the family Eupelmidae. They lay their eggs inside the eggs of plant-sucking bugs and preying mantids and also inside the larval cases (cocoons) of beetles.
“Female Eupelmids lay their eggs in their hosts’ eggs or cocoons. The wasp larvae hatch, eat the insides of their host, then pupate and emerge as adult wasps,” Ian says.
“Parasitoid females, including female eupelmids, are generally pretty good at laying the right number of eggs per host to ensure there is enough food in the parcel to feed her offspring. Most species are very small because the hosts they feed on are small.
“Eupelmids do most of their feeding as larvae. Adults may visit flowers for a sugar meal and females of some species bite hosts for a protein meal to help them produce eggs.
“Some Eupelmid species might be able to help with biocontrol of pest stink bugs, such as the Brown marmorated stink bug. This is why we want to find out more about what species exist in Australia.”
An alien wasp from Jupiter?
Ian’s work to discover Australia’s parasitoid wasp species has not been made easier by the work of an independent and self-styled entomologist, A. A. Girault, who was active in Australia in the early 20th century.
“Girault self-published many of his research papers without any peer review. He was obsessed with parasitoid wasps and described many species which he or his colleagues had collected, but he also described things that don’t exist from places that don’t exist,” Ian says.
One such paper is titled ‘Some Gem-like or Marvellous Inhabitants of the Woodlands Heretofore Unknown and by Most Never Seen nor Dreamt of’.
Another self-published paper describes a parasitoid wasp from ‘a naked chasm on Jupiter, August 5th, 1919’.
“Apparently this alien wasp was ‘vacant’, ‘shadowless’ and ‘visible only from certain points of view’. He seems to have based the description on an entomologist whom he didn’t like,” Ian says.
Parasitoid flies
Wasps are not alone in living a parasitic lifestyle. Seven groups of insects have parasitoid species.
Keith Bayless, a research scientist at ANIC who specialises in flies, says the parasitoid strategy has evolved multiple times among many different groups of flies.
“Flies parasitise a much broader range of hosts including flatworms and barnacles, not just insects and spiders. Bot fly larvae grow inside the flesh of mammals, including humans, and may kill small rodents" he says.
Even the endearing bee flies, which are mimics of bees, are parasitoids. Some species attack the larvae of solitary bees. Others target the larvae of other insect groups, such as, ironically, wasps.
Australian aliens abroad
Rabbits, cane toads, dandelions, mynas, rats, cabomba – there are hundreds of ‘alien’ species on our shores.
But Australia has exported alien species overseas too. This includes insects that have hitched rides on eucalypts exported overseas for timber plantation. For example, the gum tree weevil, Gonipterus scutellatus.
“Any time a species travels to a place in which it is alien, there’s a risk of it becoming a pest,” Ian says.
Ian recalls working with a South African researcher who visited Australia to search for parasitoid wasps that could be used for biocontrol of Australian insects.
"He found many different parasitoid wasp species and kept searching until I was able to tell him he was seeing the same species over again," Ian says.
"Parasitoid wasps regulate insect numbers in nature and for this reason they are useful for biocontrol.
"Accurate taxonomy is vital for the biological control of alien species. It turns out that the gum tree weevil is, in fact, a complex of very similar looking species and its biological control around the world will depend on correctly matching weevil and parasitoid species."
Finally, Ian reminds us the spirit of A.A. Girault lives on in the common names of some parasitoid wasps.
“The natural enemies of the gum tree weevil include the delightfully named fairy wasps. If you prefer more martial names for your biological control agents, the samurai wasp (a species of scelionid wasp) is definitely going to be your tiny warrior of choice to control the Brown marmorated stink bug," Ian says.