The adult fly punctures holes in leaves, making them unsalable, and lays eggs. The subsequent larvae "mine" the leaves, damaging them further. Bennison is leading a Horticultural Development Company project FV 408 to identify viable controls.
"Broad-spectrum pyrethroids don't kill the adult flies, and nor do other pesticides, but they may kill its natural enemies," she said.
But while none of the pesticides so far tested caused any significant reduction in puncturing, a surprising finding was that around untreated leaves the larvae had played host to two species of parasitoid wasps.
"It doesn't look as if pesticides are going to be the answer, but we did identify natural parasitoids, of which there seem to be plenty," said Bennison.
"Use of selective pesticides will hopefully not affect them and it would be a lot less expensive to use what's already out there."
In the absence of a clear chemical or biological control though, fleecing crops at periods of highest risk "may give the best control", Bennison suggested.