Studies on the Ox Warble Flies,Hypoderma lineatumandHypoderma bovis

Abstract

A historical account of the Ox Warble Flies, Hypoderma lineatum and H. bovis, is given and the economic importance of the two species is discussed. Certain aspects of their biology and control have been studied over a period of several years in South Wales culminating in intensive investigations in the years 1945 and 1946.The adults of H. lineatum emerge from their puparia in early May and those of H. bovis a month later. The adults of both species in their persistent endeavours to oviposit, worry cattle, whenever the weather is sunny and calm, from the end of May to early September but they tend to avoid the vicinity of water and shade.The degree of incidence is high in Britain, at least in South Wales, judging by the larval populations present in the backs of cattle. Over 80 per cent. of the cattle included in the surveys conducted in 1945 and 1946 harboured infestations of varying intensity; in one case 152 larvae were recorded on a Shorthorn heifer.The larvae spend, on an average basis, 42·5 days in the subcutaneous tissues of the backs of their hosts. They begin to depart in order to pupate much earlier than is normally assumed to be the case in Britain, more particularly in Worcestershire, where the proportion of larvae pupating prior to March 28th was as low as 1·4 per cent. compared with over 20 per cent. in the present studies.The marked variations commonly observed in the seasonal incidence of the larvae in their final instars on cattle are correlated with the relative prevalence of the two species in different districts.The incidence of both species, judging by the intensity of infestations, is associated with the topographical conditions of the locality. For instance, herds on upland pastures are generally less liable to severe attacks than those on lowland farms.Cattle under three years old normally carry much heavier infestations of the larvae of both species than those exceeding this age when kept under identical conditions during the oviposition period.Diphenyl-dichloro-trichlorethane and benzene hexachloride preparations are ineffective for destroying the larvae, at least in their final instars, but emulsions of the former insecticide when applied in the form of a spray to the legs and flanks of cattle during the period of oviposition proved highly promising and warrant further investigations.