| Summary: | Coptotermes formosanus was used as bait to isolate pathogenic fungi from soil. Fifteen pathogenic fungal isolates were obtained, all either Metarhizium anisopliae (six isolates) or Beauveria bassiana (nine isolates). There were no differences in numbers of fungal isolates from the three sampling locations. However, significantly more isolates were found in woodlands (eleven) than in pastures (four). Median lethal doses (LD50s) of these fungal species to C. formosanus were interspersed, indicating that fungal isolates rather than species had the greatest effect on virulence. In vitro growth characteristics were significantly correlated with virulence against termites, suggesting that fungal virulence might be predicted in vitro rather than by bioassay. Conidial production on termite cadavers increased significantly over 11 days post-death. Effects of isolates of M. anisopliae and B. bassiana on in vivo sporulation were significant. B. bassiana isolates could be categorized into a group with high total sporulation (day 11) and low quick sporulation (on days 2 and 3), while M. anisopliae isolates fell into another group with high quick sporulation and low total sporulation. Conidial production was significantly higher in vitro than in vivo. Correlation between in vivo and in vitro conidial production was positive and significant. This may allow preliminary in vitro screening of a large number of isolates for high in vivo sporulation.
Fungal species and isolate significantly affected disease prevalence in termite populations. Sporulation of M. anisopliae played a more important role than virulence in producing epizootics in termites, but this was not the case for B. bassiana. Isolates characterized by quick sporulation (day 2 after death) did not produce better epizootics in termites than those with high total sporulation (day 11 after death) in either fungal species. An isolate of M. anisopliae ranked highly in all three categories (virulence, quick sporulation, total sporulation) produced better epizootics than an isolate that was inferior in all three characteristics. High temperature (35ºC) significantly reduced fungal germination rates, leading to significant reduction of epizootics. Thus, fungal characteristics other than virulence must be taken into account for the seasonal colonization approach to termite microbial control.
|
|---|
