Miner Matters

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Ophiomyia mines:

The Agromyzidae genus Ophiomyia harbours species with widely divergent biologies. In many cases the larvae are borers, and are therefore of no immediate concern for us. A number of species mine in the bark of stout herbs, like Thalictrum Meadow-rue), Silene (Campion), Lathyrus (Pea), Lapsana (Nipplewort), Campanula (Bellflower); their mines often are quite long and narrow.

At the other extreme, a few species are full-blown leaf miners, like the one that gave the genus its name, because of its snakelike corridor mine: O. maura, a miner of Solidago virgaurea (Goldenrod)- (the Greek word ophis means snake).

 

Mines of this species (that occur also in the UK) are unmistakable by their extreme length (up to 40 cm, or so it is written), while they remain quite narrow from beginning to end, with small frass pellets set widely apart.

But there is a small group of species that more or less bridge the two extremes of borers and miners. They occur on the Compositae subfamily Liguleae, that is characterised by having milky latex and ligulate flowers. The larvae live in the hollow midribs of the leaves. During daytime the larvae can mostly be found at the extreme base of the leaf, in the midrib.

 If you do not pick the leaves carefully enough, and leave a part of the leaf base on the plant, you mostly miss the larva (and the possibility of a definite identification). With a little experience you can, keeping the leaf against the light, recognise the larva's hiding place in the base of the midrib (here in Lapsana):

 
 

 

When you cut away the sclerotised tissue that caps of the larva's living tube, a relatively slender larva becomes visible, together with a black mass of frass (practically all frass of the whole mine if concentrated here):

 

 

 

 

 

Storing mines in a refrigerator actually simulates night for the larvae. After a while in the fridge you may find that they have left their dung heap hiding place, and start feeding.

Starting somewhere along the midrib (but mostly in the distal half of the leaf), the form irregular galleries. They also often make a long gallery on top of the midrib.

 

 O.maura mine on Sonchus (Sow-thistle)

 

O.maura mine on Taraxacum (Dandelion)

 

 

 

O.maura mine on Taraxacum (Dandelion)

 

The resulting mine may remind one of Scaptomyza flava, but that species doesn't live on Compositae.

 

 

 

However, they often have an uncanny resemblance with the mine of Liriomyza strigata, which is a very common and polyphagous miner (photo opposite, on Sonchus (Sow-thistle)).

 

 

 

 

Yet it is not difficult to tell the mines apart. The branches that diverge from the midrib are free of frass in Ophiomyia; only rarely a few traces are present at the place where the larve has left the midrib for foraging.

Liriomyza strigata on the contrary produces frass while it mines, and, like in most Liriomyza species, it is in long streaks (seen in the photo opposite).

Moreover, L. strigata larvae leave the mine shortly before pupation, while Ophiomyia pupates in its usual hiding place at the basis of the midrib.

Identification at the specific level is not so easy, as it has to be done on the shape of the mandibular teeth and the anterior spiraculum of the larva.

 

 

 

Images: Willem Ellis, 2004

 

Willem N. Ellis - July 2004
Newsletter of leafmines.co.uk                                                                                                          July 2004