I was mooching around the garden the other day, thinking it as time to cut the hedge, when I noticed a few marks on one of the leaves of an Aquilegia. I have not idea what the names of this strain is, but it’s almost certainly a mongrel. Looking closer all the leaves were affected, and not just on this one plant but on all 10 plants in the garden. Leaf miners are a bit of a mystery to me, nothing new there the wife would say, so I had a go at trying to identifying what was the cause. It turns out that leaf mines can be caused by flies, moths or beetles. Each species creates a distinctive mine, and is usually specific to one or two plants hosts. So how difficult could it be? For once it was fairly easy this time, but this is rarely the case. My first port of call were two great websites dedicated to leaf mines in the UK: ukflymines.co.uk and leafmines.co.uk. There are only two leaf miners that use Aquilegias as a host in the UK, and both mines are very different. And the one I have is Phytomyza minuscula, a small fly.
P. minusclua creates a short linear but irregular mine in the leaf. As the larva eats its way through the internal layer of the leaf it leaves it’s frass behind in a pattern that creates black strips along the middle of the mine. It also turns out that the pattern of the frass within the leaf mine is also a diagnostic sign in determining species. In the UK P.minusclua also used Common Meadow Rue, Thalictrum flavum as a host plant as well. The mines can be found from June through to September.
The leaf mines are relatively easy to spot once you’ve got your ‘eye in’. The adult flies though are a different matter. They are small, and I am sure are a challenge to identify. For this you would need experience, a microscope and time – none of which I have. So seeing the adult cold be a challenge, and in fact because they are so small I may have seen one but dismissed as “too small to bother” (TSTB). But there are photographs available on the Encyclopaedia of Life website. I might try to raise a few through to adulthood – all I have to do is find out how.
Another fascinating fact about P.minusclua are the number of parasitoids that hunt down the larvae. UKleafmines.co.uk list 12 known parasitoids. To me that’s an impressive list to other insects hunting you down so that you can be eaten from the inside. Gruesome.
- Chrysocharis orbicularis
- Chrysocharis pentheus
- Closterocerus trifasciatus
- Hemiptarsenus unguicellus
- Diglyphus chabrias
- Diglyphus isaea
- Pnigalio soemius
- Opius minusculae
- Opius pallipes
- Phaedrotoma minusculae
- Phaedrotoma staryi
- Pitkin,B., Ellis,W., Plant,C and Edmunds,R. Phytomyza minuscula. http://www.ukflymines.co.uk/Flies/Phytomyza_minuscula.php. Accessed 2017.07.19.
- Leaf Mines UK. Phytomyza minuscula. http://www.leafmines.co.uk/html/Diptera/P.minuscula.htm. Accessed 2017.07.19.
- NBN Phytomyza minuscula. https://species.nbnatlas.org/species/NBNSYS0000029800#overview. Accessed 2017.07.19.