The work has demonstrated that one of the more important areas of Scotland where Dicrocoelium dendriticum is endemic carried infected colonies of Helicella itala which live in association with the ant Formica fusca. Workers of the ant were shown to acquire typical metacercarial cysts after the ingestion of slime balls, and the cysts gave rise to mature lancet flukes in sheep and hamsters, eggs appearing in the faeces after 56 and 48 days respectively. Higher egg counts were obtained from hamsters to which more cysts were administered. This is the first occasion on which an ant intermediate host has been demonstrated for Dicrocoelium in Britain.
Three species of blood-feeding flies (Stomoxys calcitrans, Haematopota pluvialis and Hydrotaea irritans) were fed for five minutes on a bullock persistently infected with bovine virus diarrhoea virus (BVDV) containing 10(4.5)TCID50 non-cytopathic BVDV/ml serum, then subsequently fed on BVDV-free seronegative animals maintained in isolation. Virus was isolated from recipient animals between days 5 and 10 using H pluvialis, and up to 72 hours after transmission with S calcitrans; virus isolation was negative using H irritans. Positive seroconversion results obtained with H pluvialis gave a steadily increasing antibody titre. BVDV was recovered from flies 96 hours (four days) after an infective feed for H pluvialis and S calcitrans, but for two hours only for H irritans.
The biology and population fluctuations of the non-biting Muscid Hydrotaea irritans (Fall.) were studied in two contrasting areas of Surrey using a standardised catching technique at selected sites, by analysing catches and by dissecting the collected flies. Following the first appearance of adults in early June, catches reached a maximum in late July, the males having fallen to a small proportion by early July. During August catches gradually fell, remaining at a relatively low level for the rest of the summer. The complete life-cycle, starting with eggs from caged fly colonies, took 295 days under sheltered outdoor conditions. The fly is univoltine, with three larval instars; larvae leave the egg in the second instar which is a brief, saprophagous stage, while the third, principal stage is predatory on other insect larvae. Overwintering normally occurs as a late-stage larva. Flies collected from sheep-grazing areas in Northumberland were shown, using serological methods, to have fed predominantly on cattle blood protein.
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