Biological control of the nematode parasites of sheep and cattle by a nematode-trapping fungus

Chapters one to three review literature relevant to the thesis. The first chapter deals with the nature of nematode parasitic disease in livestock, the factors affecting its distribution and frequency of occurrence in Australia, and the production losses caused by these parasites. The second chapter deals with the effects of parasitism on the host animal including changes to metabolism and physiology caused by parasitic disease. The epidemiology of nematode-parasitic disease is examined and control methods discussed, particularly with regard to the past reliance on anthelmintics and the emergence of anthelmintic-resistant parasitic nematodes. Alternatives to the use of anthelmintics, including breeding for parasite resistance in livestock, vaccination and biological control, are discussed. Chapter three contains a review of the literature pertaining to nematophagous fungi and their potential as biological control agents against animal-parasitic nematodes. Chapter four introduces the experimental program conducted during the project and the following five chapters contain procedures used and the results of these experiments. Results are discussed in chapter ten. A survey of soil samples taken from Tasmanian sheep-grazing properties examined the frequency of occurrence of nematode-trapping fungi in sheep pastures, and the fungi isolated were compared for their ability to grow and trap nematodes on laboratory media. The predaceous fungus, Arthrobotrys oligospora, was chosen for use in further experiments. The effects of fungal inoculum density and prey population size on fungal predacity were examined in chapter six. Chapter seven reports on investigations into fungal spore formulations including attempts to encapsulate fungus for protection within the ruminant stomach and methods for collecting fungal spores from mature grain cultures. Chapter eight reports on in vitro and in vivo experiments on the ability of fungal spores to survive passage through the digestive tract of sheep and cattle. Chapter nine reports on glasshouse trials in which various fungal treatments were applied to faeces from a parasitised sheep on pasture swards. Yields of infective larvae on pasture herbage were compared. Soil inoculation had little effect on pasture infectivity but when faeces were sprayed with a suspension of spores, reductions of up to 90% were obtained. The timing of the spray in relation to deposition of faeces had a significant effect on the ability of the fungus to reduce the numbers of infective larvae reaching the herbage.