Sunday, 1 December 2013

Late November 2013

Although the weather has been getting colder there are still some flies about. In particular beating dead leaves on trees and shrubs can often dislodge overwintering Tephritid flies. These flies form galls on various plants but particularly members of the Asteraceae, daisy family. Each fly species is associated with particular plant species and the galls are firmed in particular parts of the plant. One of the commonest species is Urophora cardui, which forms a distinctive gall in the stems of creeping thistle Cirsium arvense. Several of these were present near Yardley Chase on 21st November.

Swollen stem of creeping thistle caused by the Tephritid fly Urophora cardui. The fly itself is very distinctive, having black wing markings of two inverted U shapes that are joined on the trailing edge of the wing. If the two U shapes are not joined, this is another species.

Urophora cardui

Apart from the above gall, adults of other Tephritid flies have been noted over the past couple of weeks: Tephritis formosa, T. neesii and T. hyoscami all in the Yardley Chase area. All of these flies have distinctively patterned wings and are frequently referred to as "picture wing flies". The term covers members of several families, not just the Tephritids. 

It is possible to find the galls of these flies in the heads of various thistles in winter. If you squeeze the dead flower head you can sometimes feel a hard capsule inside, which is the gall. It is possible to raise the adult fly from the gall to confirm which species has made it.

Other signs of the larvae of flies in winter can be leaf mines. Here is blotch mine in the leaf of hedge woundwort Stachys sylvatica. This is caused by the Agromyzid fly Amauromyza labiatarum. It was found at Yardley Chase.

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