By David Honsberger and Mark Wright
Mymarommatoidea is a group of miniscule but very beautiful wasps, around 0.5 mm in length – which to our eyes look like specks of dust.
They’ve been elusive to entomologists, and were the last major group of parasitoid wasps about which nearly nothing was known regarding their biology. We have scant records of what they do in the world and none of what they develop on. In fact, living individuals in their natural environment have never been recorded in the scientific literature.
We discovered a species of Mymarommatoidea emerging, somewhat consistently, from branches of a banyan tree on the UH Mānoa campus. It turned out this wasp was also an undescribed species. We named it Mymaromma menehune, the species name “menehune” because like the menehune, they are small and elusive, rarely seen.
We took this opportunity to try and see what it was doing. We collected branches, scanned them under the microscope for any eggs laid on them, on and under the bark, and isolated the eggs in gel caps to see what would come out. A few of the mymarommatids came out. We reared some of the same eggs and found they belonged to bark lice. In this way, the parasitoid-host association was confirmed. This species of mymarommatid parasitizes bark lice eggs. This is the first confirmation of the host species for these wasps, a mystery since their first discovery 100 years ago!
These wasps have some very unique body structures. For example, the back of their head can expand like a bellows, their mandibles push outward instead of cut, they have beautiful fore wings with long setae around their edges, and hind wings consisting of just a stalk that forks at its end.
Because of their tiny size and short ovipositors, it was previously proposed they are likely parasitoids of arthropod eggs. Given their unique anatomy and patterns in collection records, it was suggested they might parasitize eggs of bark lice. Maybe most interestingly, this was suggested in part because the wasps may use their expandable head and reversed mandibles to break out through the flexible shell of bark lice eggs, and the mandibles to open a tunnel to pass through the silk that some species of bark lice produce around their eggs. This work confirms these long-standing hypotheses.
Although our discovery is not immediately applicable to agriculture, its implications are of a more fundamental sense: what is out in the world? And what do those things do? For tiny creatures like these, which often go unnoticed by us big, clumsy creatures, there is still much that is unknown. Such creatures may also be important because we have a very nice radiation of endemic bark lice in Hawaiʻi, though we have no idea yet if it has any association with them.
This type of work does have indirect implications in for applied ecology and agriculture, in that it contributes to a deeper understanding of biodiversity. The more we know about parasitoids, no matter how obscure, the more efficiently we can develop biological controls for invasive species in the future.
And, they are beautiful creatures.
Read the full article here in the Journal of Hymenoptera Research.