BR. J. ENT. NAT. HIST., 6: 1993 159 



A REVIEW OF THE BRITISH OPOMYXIDAE (DIPTERA) 



C. M. Drake 

 22 Park Road, Deeping St James, Peterborough PE6 HND. 



The acalyptrate family Opomyzidae has about 50 species in four genera worldwide, 

 found mostly in the Holarctic. They are small, yellow to dark-brown flies with at 

 least the apex of the wing clouded in most species and often with other wing spots. 

 Vockeroth (1987) provides a full family description. The larvae feed within the stems 

 of Gramineae and a few species are pests of cereals and rye-grass ley in Britain and 

 other parts of Europe and in Russia (Balachowsky & Mesnil, 1935; Nye, 1958). 



The Palaearctic catalogue (Soos, 1984) lists nine Opomyza, eighteen Geomyza and 

 the single species in a third genus, Anomalochaeta guttipennis (Zett.). Since then, 

 another nine Geomyza and one Opomyza have been described (Nartshuk 1984, 1992, 

 1993; Drake, 1992; Carles-Tolra, 1993). Most of these species were described or re- 

 described by Czerny (1928) who also provided a nearly comprehensive key to the 

 Palaearctic fauna. Collin (1945) provided a key to thirteen then known from Britain, 

 and to these Andrewes (1964) added G. angustipennis Zett. and Drake (1992) described 

 G. subnigra. Vockeroth (1961) pointed out the presence of two species under 

 "combinata" of Collin (1945) and these are now known to be balachowskyi Mesnil 

 and hackmani Nartshuk. Sixteen species are therefore included in the present paper. 



Several papers have catalogued the opomyzids found in individual countries in 

 Europe or Russia, sometimes including keys (e.g. Hackman, 1958; Trojan, 1962; 

 Stackelberg, 1970; Martinek, 1978a; Greve, 1981; Nartshuk, 1993). These authors 

 illustrated the genitalia of some species but a number remain unfigured. The chaetotaxy 

 of both genera is remarkably uniform so that keys place strong emphasis on wing 

 pattern and coloration but relatively little on morphology. However, the genitalia, 

 especially those of Geomyza, are often distinctive, and their examination is sometimes 

 essential for identification. 



Existing keys, especially that of Collin (1945), have provided the main characters 

 used in the following key which has been arranged so that, as far as possible, common 

 species are placed towards the beginning within each genus. This paper uses the names 

 as currently understood and does not constitute a taxonomic revision. Only a few 

 type specimens have been seen and all the figures except one are of British specimens. 

 McAlpine (1981) has been followed for morphological terminology; refer to Fig. 4d. 

 Unpublished records on distribution and dates of capture have been collected by the 

 author. Dimensions are given in Table 1. 



Key to the British species 



1 Wing with well developed alula and small anal vein; basal and apical setae of the 

 scutellum approximately equal in size; arista pubescent. Predominantly yellow or 

 greyish yellow, medium to large (for the family) flies Opomyza, 2 



— Wing without alula or anal vein; apical setae of the scutellum long, the basal 

 pair very short; arista short plumose (in British species). Mostly small to medium- 

 sized flies with moderately shiny black abdomens and black, reddish or yellow 

 thoraxes Geomyza, 7 



2 Costal margin darkened beyond vein R,. Pleura with brown marks. Middle femora 

 of males with dense posteroventral bristles {germinationis group) 3 



— Costal margin clear except for apical spot. Pleura entirely yellow. Middle femora 

 of males simple. (Jlorum group) 4 



