Studies on the possible role of cattle nuisance flies, especially Hydrotaea irritans, in the transmission of summer mastitis in Denmark

The summer mastitis pathogens Actinomyces pyogenes, Peptococcus indolicus, Bacteroides melaninogenicus ss. levii, Fusobacterium necrophorum and Streptococcus dysgalactiae were isolated from the polyphagous symbovine dipterans Hydrotaea irritans (Fallén) and Morellia sp. caught around dairy heifers on pasture, but not from the haematophagous species Haematobia irritans (L.), Haematobosca stimulans (Meigen), Culicoides sp. and Simulium sp. Secretions from clinical cases of summer mastitis proved to be sources of summer mastitis bacteria for more than 3 weeks despite antibiotic treatment and teat amputation. Taking into account the seasonal activity pattern of Hydrotaea irritans and its topographical distribution on grazing cattle, it appears evident that this fly may play a central role in the establishment and maintenance of the bacterial contamination with summer mastitis pathogens on the teats of healthy cattle. In the present study the survival of A.pyogenes and P.indolicus for 7 days in experimentally infected Hydrotaea irritans, as demonstrated by the recovery of these microorganisms from agar plates exposed to live infected flies, is described. However, experimental transmission of summer mastitis from sick to healthy heifers by Hydrotaea irritans proved unsuccessful.     

A novel brood‐site pollination mutualism?: the root holoparasite Thonningia sanguinea (Balanophoraceae) and an inflorescence‐feeding fly in the tropical rainforests of West Africa

The Balanophoraceae is a unique angiosperm family that fully parasitizes the roots of trees. Although the pollination systems of several genera in this family have been reported, little is known of their diversity. In the present study, we investigated the pollination biology of Thonningia sanguinea (Balanophoraceae) in the tropical rainforests of Guinea, West Africa. Female flies of the families Muscidae and Calliphoridae as well as Technomyrmex ants frequently visited flowers to consume nectar secreted from inflorescences. While feeding, their bodies attached to anthers or pollen grains. The most abundant flower‐visiting fly, Morellia sp. (Muscidae), was observed laying eggs on T. sanguinea, and the larvae fed only on the vegetative tissue of decaying male inflorescences. Our findings provide a new candidate of pollination mutualism involving plants that provide brood sites for their pollinators.     

Variation in density of cattle-visiting muscid flies between Danish inland pastures

Abstract. The density of cattle-visiting flies (Muscidae) and the load of black-flies (Simulium spp.) were estimated in twelve and eighteen inland pastures in Denmark in 1984 and 1985 respectively. No differences in the geographical distribution pattern of the predominant cattle-visiting Muscidae were recorded, whilst the relative abundance and density of the species and the total fly-load varied considerably between pastures. In most cases the mean loads of Haema-tobia irritans (L.) and Hydrotaea irritans (Fall.) on heifers varied significantly in relation to site topography and shelter. These crude site variables explained 65–98% of the variation in densities of horn flies and sheep head flies observed between pastures. Highest densities of Hydrotaea irritans were primarily associated with permanent, low-lying, fairly sheltered grassland sites, whereas the density was low in temporary, dry, wind-exposed pastures. A comparable relationship was found for Haematobia irritans. With Haematobosca stimulans (Mg.) and Morellia spp. no relation between grassland environment and fly density was detected.