Platypalpus ochrocera (Collin) (Diptera, Hybotidae) from exposed riverine sediments with a description of the female

Summary:\ud The female of the hybotid Platypalpus ochrocera (Collin, 1961) is described and the relevant British and European keys are modified to take account of newly recognised characters. Distributional and ecological information on P. ochrocera is presented, and an apparent association with exposed riverine sediments discussed. Platypalpus\ud velocipes Frey, 1943 is newly recorded for Slovakia.\ud \ud Introduction:\ud In 2015 I operated emergence traps set on exposed riverine sediments on the King Water (NY525635), a tributary of the River Irthing in north Cumbria. Four standard soil emergence traps with a footprint of 60cm by 60cm were each set on different substrate types. A valance around the base of each trap was buried in the substrate, ensuring that all insects emerging from the soil surface within the trap were retained. At the apex of each trap, a collecting bottle containing 50% antifreeze was used to kill and preserve emergent individuals. The traps were operated from 7 June to 19 July and serviced on a weekly basis, apart from the final sample which covered a two week period. One trap was installed on loose, vegetated sand deposited on the riverbank and in the sample from this trap for the period 3-19 July were 30 specimens of Platypalpus ochrocera (14 males and 16 females). There were also seven specimens of P. interstinctus (Collin), two of P. niger (Meigen) and a single female P. articulatoides (Frey). I also swept 10 specimens (5 males and 5 females) of P. ochrocera from vegetated sandy shingle on the Ettrick Water, Selkirkshire (NT275144) on 15.viii.2015.\ud Whilst the male specimens of P. ochrocera keyed out readily enough using Grootaert and Chvála (1992), the females were more problematic, running to P. articulatoides by dint of their darkened postpedicel, pale palpi and coxae, but lacking the distinctly annulated tarsi of that species. It is apparent that the key does not take account of the darkened postpedicel of female P. ochrocera and consequently female specimens of this species will not key out satisfactorily.\ud Collin (1961) described P. ochrocera new to science from just a single male and a later account of the species (Chvála 1989) also appears to be based on male specimens only. There are no female specimens of P. ochrocera in the Chvála Collection at the Oxford University Museum of Natural History, or in the collection of the Russian Academy of Sciences in Moscow (I. Shamshev pers. comm.). It seems worthwhile to provide here a description of the female of P. ochrocera and to adapt the relevant parts of the British and European keys to take account of this new information on the characters of female P. ochrocera