Effect of different times of administration of the nematophagous fungus Duddingtonia flagrans on the transmission of ovine parasitic nematodes on pasture - a plot study.

Investigations were made into the timing of administration of Duddingtonia flagrans as a biological control agent against ovine parasitic nematodes in cluding stongylid and Nematodirus spp. Faeces from 3-4 months old male lamb s were deposited onto pasture plots that had never been grazed by sheep. Th e trial was conducted over two consecutive years (1998 and 1999), For both years, the following three plot types were involved: Sim plots had faeces c ontaining nematode eggs and Duddingtonia flagrans spores deposited simultan eously; Post plots had faeces containing nematode eggs followed 2 weeks lat er by faeces containing D. flagrans spores alone; Control plots had faeces containing only nematode eggs; Prior plots (included in 1999) had faeces co ntaining D. flagrans spores alone followed 2 weeks later by faeces containi ng nematode eggs. In each year, two deposition periods were involved: July and August in 1998 and June and July in 1999. During the first year pasture samples were collected at 2, 4, 6, 8 and 12 weeks after initial deposition . In 1999, additional samples were collected at 10, 16 and 20 weeks. Larvae were extracted from the pasture samples and counts performed to estimate t he number and species of infective third-stage (L-3, larvae) present. The n umber of third-stage strongylid larvae on pasture was significantly lower o n Sim plots compared to the remaining plot types for both years at all depo sition times (P < 0.001). This was also the case for the number of Nematodi rus infective larvae in August deposition plots in 1998 (P < 0.02). There w as no significant difference between treatments in both deposition times in 1999 and July deposition plots in 1998 for the Nematodirus data. These res ults suggest that D. flagrans, if deposited at the same time as parasite eg gs prevents transmission of third-stage larvae from the faecal deposit onto pasture, including occasionally Nematodirus species, but does not have an effect on third-stage parasitic nematode larvae in the surrounding soil. (C ) 2000 Elsevier Science B.V. All rights reserved.