The thin, flexible, and mobile ovipositor of some female insects, perfected over thousands of years of evolution, can carry substances and drill into various substrates. Although its structure is well studied, many of its functions remain a mystery.
Researchers from Saratov State University and Moscow State University spotted interesting, unusual oviposition behaviour in the parasitoid wasp Eupelmus messene: it used its ovipositor to drill through the wall of a polystyrene Petri dish and lay an egg outside the dish.
This is the first time such behaviour has been observed and recorded.
E.messene is a parasitoid of the gall wasp Aulacidea hieracii, which forms a gall on the stems of the hawkweed Hieracium×robustum. The female of E.messene then drills the walls of the gall with its ovipositor in search of a gall wasp larva and, upon finding it, lays an egg next to it.
The researchers reared 56 females from galls of H.×robustum collected near Saratov, Russia. Of them, they placed 18 in Petri dishes without host galls, and later observed five of those wasps drilling into the walls of the Petri dishes.
The team followed the behaviour of one wasp: drilling each perforation in the polystyrene wall took more than two hours, during which the insect often paused to eat, drink water, or wash. In the end, it managed to completely pierce the plastic wall and lay an egg on the outside of the Petri dish. It drilled multiple holes, even after being transferred to a different Petri dish.
“We distinguished four steps of drilling: pushing movements, rotational movements, ejection movements, as well as the cementing step. However, in natural gall, we never observed ejection movements. We suppose that such a type of movement is required to rake out plastic particles, which is unnecessary for more elastic plant gall substrate,” write the authors in their study, which was published in the Journal of Hymenoptera Research.
After laying the egg, the female carefully cemented the drilled perforation with an unknown biological substance, likely to keep it safe from the impacts of changing temperatures, water, and microorganisms.
Unlike galls, which usually have an opaque and dense structure, the transparent Petri dish provided a clear view of the whole drilling and oviposition process, allowing the researchers to study it closely.
It is still unknown why the wasp behaved this way, but the scientists believe we can learn a lot from this observation: “Studying in detail the drilling behavior of parasitic mycrohymenopterans can be useful in medicine for the creation of minimally invasive guided probes in neurosurgery, the development of orthopedic surgical instruments, needle biopsies using functionally graded tools,” they write in their paper.
Research article:
Nikelshparg MI, Nikelshparg EI, Anikin VV, Polilov AA (2023) Extraordinary drilling capabilities of the tiny parasitoid Eupelmus messene Walker (Hymenoptera, Eupelmidae). Journal of Hymenoptera Research 96: 715-722. https://doi.org/10.3897/jhr.96.107786
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