The efficacy of two isolates of the nematode-trapping fungus Duddingtonia flagrans against Dictyocaulus viviparus larvae in faeces

A series of experiments was carried out to examine the effects of two diffe rent isolates of the nematode-trapping fungus Duddingtonia flagrans to redu ce the number of free-living larvae of the bovine lungworm, Dictyocaulus vi viparus. A laboratory dose-titration assay showed that isolates CI3 and Tro ll A of D. flagrans significantly reduced (P < 0.05 to P < 0.001) the numbe r of infective D. viviparus larvae in cultures at dose-levels of 6250 and 1 2,500 chlamydospores/g of faeces. The larval reduction capacity was signifi cantly higher for Troll A compared to CI3 when lungworm larvae were mixed i n faecal cultures with eggs of Cooperia oncophora or Ostertagia ostertagi a nd treated with 6250 chlamydospores/g of faeces. Both fungal isolates showe d a stronger effect on gastrointestinal larvae than on lungworm larvae. Two plot trials conducted in 1996 and 1997 involved deposition of artificial f aecal pats containing free-living stages of D. viviparus and C. oncophora o n grass plots. Herbage around the pars was collected at regular intervals a nd infective larvae recovered, counted and identified. These experiments sh owed that both D. flagrans isolates reduced the number of gastrointestinal as well as lungworm larvae in faecal pats. During both plot trials, the tra nsmission of C. oncophora larvae, but not D. viviparus, from faecal pats to the surrounding herbage was clearly affected by climatic conditions. After collection of faecal pats from the grass plots one month after deposition, the wet and dry weight of pats as well as organic matter content were dete rmined. No differences were found between the fungus-treated and nan-treate d control pats. This indicated that the rate of degradation of faeces was n ot affected by the addition of the fungus. (C) 1999 Elsevier Science B.V. A ll rights reserved.