A method to evaluate relative ovicidal effects of soil microfungi on thick-shelled eggs of animal-parasitic nematodes

Abstract

Thick-shelled eggs of animal-parasitic ascarid nematodes can survive and remain infective in the environment for years. The present study evaluated a simple in vitro method and evaluation scheme to assess the relative effect of two species of soil microfungi, Pochonia chlamydosporia Biotype 10 and Purpureocillium lilacinum Strain 251 (Ascomycota: Hypocreales), on the development and survival of eggs of faecal origin of three ascarid species, Ascaridia galli (chicken roundworm), Toxocara canis (canine roundworm) and Ascaris suum (pig roundworm). Ascarid eggs were embryonated on water agar with or without a fungus, and the resulting viability of the eggs was evaluated on days 7, 14, 21, 28, 35 and 42 post exposure (pe) by observing eggs in situ. On days 7-42 pe, P. chlamydosporia had reduced the viability of A. galli and T. canis eggs by 64-86% and 26-67%. Corresponding reductions for P. lilacinum Strain 251 were only 15-29% and 4-28%. In contrast, A. suum eggs were extremely resistant to both fungi (2-4% reduction). The differences in results are likely due to different morphologies and chemistry of the egg shell of the three ascarid species. The current in vitro method and evaluation criteria allow for a simple, repeatable and non-invasive evaluation of the ovicidal effects of microfungi. This study demonstrates that P. chlamydosporia Biotype 10 may be utilised as a biocontrol agent to reduce A. galli and T. canis egg contamination of the environment.

Viability and development of Ascaridia galli eggs recovered in artificial media followed by storage under different conditions

“…In the present study, antimicrobial agents were not used during incubation at 26°C and it is possible that reduction in egg viability over time may be attributed to microbial degradation. It has been shown in vitro that bacterial (Bottjer et al ., 1985; Tian et al ., 2007) and fungal (Terrill et al ., 2004; Thapa et al ., 2015b) activities can damage eggs of parasitic nematodes. Anecdotally, this was infrequently observed during microscopic observation of the samples in the current study probably due to the embryonation medium (0.1 N H 2 SO 4 ) limiting microbial growth.…”

Survival and development of chicken ascarid eggs in temperate pastures

“…(Tarbiat et al 2015) and biotic factors (e.g. microfungi) can influence the survival of chicken ascarid eggs (Thapa et al 2015 b ). Compared with the eggs buried in the spring, the recovery of eggs buried in the winter decreased more slowly, but the prolonged delay in onset of embryonation during colder months seemed to reduce the viability of eggs.…”

“…Laboratory experiments have shown a substantially higher in vitro mortality of chicken ascarid eggs in non-sterilized soil than in sterilized soil (Thapa et al 2015 c ). This may be due to soil microbiota, including egg-degrading microfungi such as Pochonia chlamydosporia and Purpureocillium lilacinum (Thapa et al 2015 b , c ). In addition, soil bacteria can degrade eggs of plant-parasitic and soil nematodes (Chen et al 2006; Padgham and Sikora, 2007).…”

Individual and Combined Application of Nematophagous Fungi as Biological Control Agents against Gastrointestinal Nematodes in Domestic Animals

“…It has been found to be able to reduce the number of nematode eggs in the feces of dogs and horses (Table 2), but the effect was not as good as that of Po. chlamydosporia [60,67]. The fungus presents a safety risk for humans and animals because it can produce neutral straight-chain peptide toxins (paecilotoxins) [81,82].…”