Nematophagous fungi in pasture: colonisation of sheep faeces and their potential for control of free-living stages of gastro-intestinal nematode parasites of sheep

Sheep faeces placed on a pasture in New Zealand in February and April were retrieved at intervals up to 28 days and examined for fungi that parasitise nematodes (nematophagous fungi). Monacrosporium haptotylum, Harposporium bysmatosporum, H. helicoides and a Nematoctonus sp. were present, respectively, in 37, 22, 13 and 8% of 283 samples retrieved in February and from 29, 14, 11 and 15% of 200 samples retrieved in April. Fungi entered faeces rapidly, being present in 35 and 54% of samples retrieved after 3 days in February and April, respectively. The ability of migrating soil nematodes to carry fungal propagules from soil into faeces was assessed in 2 laboratory experiments. Sheep faeces separated from soil by filters that allowed passage of both nematodes and fungi was colonised by H. helicoides more frequently than faeces on filters that excluded nematodes, indicating nematodes were vectors. However, Arthrobotrys oligospora, M. haptotylum and A. brochopaga occurred in faeces independently of filter type, indicating that these species grew into faeces. Two laboratory experiments examined the ability of nematophagous fungi, when inoculated into sheep faeces containing eggs of the gastro-intestinal nematode parasite Trichostrongylus colubriformis to reduce the number that developed to third-stage larvae. Monacrosporium gephyropagum, A. cladodes, A. conoides and A. oligospora reduced the number of third-stage larvae that emerged by 54-91% (P<0.05) in comparison to a control; however, M. haptotylum and H. bysmatosporum were ineffective. In a second experiment, several species of nematophagous fungi reduced the number of third-stage larvae that emerged by 41-96% (P<0.05) in comparison to a control, while others had no effect.