In previous years I’ve reported on the 6 mistletoe insects we have in Britain – and how we know very little about them. Indeed 2 of the 6 were only discovered here in the years since 2000 and the distribution and biology of all 6 are hardly known. But all are definitely tied to mistletoe, as they eat nothing else (except the Anthocoris bug, which eats the others).
The six are: a moth Celypha woodiana (the Mistletoe Marble Moth), a beetle Ixapion variegatum (the Mistletoe Weevil), three sap-sucking bugs Hypseloecus visci, Pinalitus viscicola and Cacopsylla visci and the predatory bug Anthocoris visci
The weevil lays its eggs inside mistletoe stems and the larva develops inside, only emerging as an adult weevil and leaving a distinctive exit hole. Affected shoots often show die-back of the terminal bud. And that’s about all that is known about it. A simple life-cycle, no complications. Or none known.
However, a recent paper by Ian Thompson and Godfrey Blunt in Field Studies journal recording studies of invertebrate communities in Shropshire orchards makes an intriguing observation. The authors made a special effort to record mistletoe insects within the orchards they visited, including collecting some mistletoe shoots with bud die-back to see if weevils emerged. Some weevils did indeed emerge from some of the samples. But from others a tiny parasitic wasp emerged instead of the weevil. It was from a genus of wasps, Triaspis, that specialises in parasitising the eggs and larvae of beetles.
The obvious inference is that this wasp was parasitising the Mistletoe Weevil larvae. The wasp proved impossible to identify to species – and so may, itself, be newly discovered and might, perhaps, be a dedicated specialist only parasitising the Mistletoe Weevil. Which only eats mistletoe, itself a parasite.
So we could have a new species and a new parasite – of an insect that eats a parasite.
But no-one, yet, knows…