Friday, 7 November 2014

Fruit fly pest found in Northants

When the moth traps at Pitsford Water Reserve are checked, the non-moth by-catch is collected and distributed to various people to record what other species have occurred. This is quite valuable as a number of species turn up in the traps that are not, or not often, found by sampling in other ways. On 13th October a small yellowish fly with red eyes and a distinctive spot on the wing was taken in the woodland moth trap. I fairly quickly determined it as a fruit fly, Drosophilidae, but as I do not have a key to this family I nearly disposed of it. However I decided to try to find a match on the internet as the wing spot was so distinctive and I knew most fruit flies do not have marked wings. A quick search revealed the likely candidate was the spot-winged fruit fly Drosophila suzukii. This species comes from Japan and is widespread in South-east Asia. It has also spread widely in Europe and the USA, where it is a serious pest of soft fruit. Unlike other fruit flies, which lay their eggs in damaged fruit, the female of this species has a serrated ovipositor which she uses to cut a hole in the skin of soft fruit and then lay her eggs for the maggots to feed on the fruit flesh. It had been forcast that this fly was likely to turn up in the UK sooner or later and sure enough it did. The first record was in August 2012 at the East Malling horticultural research station in Kent, when it was caught in a trap in the soft fruit fields. A number of other records occurred in Southern England after that. It was found this year at Winterton in Norfolk, the furthest North record so far and the Pitsford record is the first for the Midlands as far as it is known. Apart from its penchant for soft fruit crops, it will also use wild soft fruit such as blackberries, so horticultural spraying will not eliminate this species from Britain. Once more global trade  has spread an alien species into our environment with unknown economic consequences.

I have attached a fairly poor picture of the fly but it shows the wing spot (only on the male). The other diagnostic  features are the male's small black combs of bristles on the first two segments of the fore tarsi. You can just see these as small black dots on the front legs in the photo. The female is identified by the serrations on the outside edge of the ovipositor. Full descriptions, good photos and details of UK records will appear in the next ecition of Dipterists Digest, due out at the beginning of December. To confirm my identification, I sent the photo and description to Peter Chandler, who did confirm it. Two more photos added showing a bit more detail.