Virulence and in vitro Characteristics of Pathogenic Fungi Isolated from Soil by Baiting with Coptotermes formosanus (Isoptera: Rhinotermitidae)
Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) was used as “bait” to isolate pathogenic fungi from soil. Ninety soil samples were collected from woodlands and pastures in the vicinities of Baton Rouge, New Orleans, and Lake Charles, LA, from which six Metarhizium anisopliae (Metsch.) Sorokin and nine Beauveria bassiana (Balsamo) Vuillemin isolates were obtained. Numbers of fungal isolates from the three sampling locations did not differ, but more isolates were found in woodlands than in pastures. 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. Among nine Louisiana and two USDA isolates of B. bassiana, LD50s ranged from 4.95 × 103 to 4.96 × 105 conidia/termite, a difference of 100×. LD50s of six Louisiana and four USDA isolates of M. anisopliae ranged from 7.89 × 103 to 1.22 × 105 conidia/termite. Survival time also was used to compare virulence; M. anisopliae infections caused significantly shorter host survival times than B. bassiana. In vitro growth characteristics were significantly correlated with virulence against termites, suggesting that the characteristics of a fungus growing on agar might contribute to estimating the fungal virulence in vivo.
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