EFFECTS OF SOIL FUNGISTASIS ON BEAUVERIA-BASSIANA AND ITS RELATIONSHIP TO DISEASE INCIDENCE IN THE COLORADO POTATO BEETLE, LEPTINOTARSA-DECEMLINEATA, IN MICHIGAN AND RHODE-ISLAND SOILS

The fungistatic effects on Beauveria bassiana were measured in soils collected from two potato fields each in Rhode Island and Michigan for 2 years. Both Michigan soils were more fungistatic than Rhode Island soils in 1986, and in 1987 one Michigan soil was significantly more fungistatic than the Rhode Island soils, but fungistasis levels varied between years. Fungistasis levels were found to increase exponentially with increases in soil pH. Pupae of the Colorado potato beetle, Leptinotarsa decemlineata (CPB), were inoculated with B. bassiana conidia and immediately incubated in the Michigan and Rhode Island soils to determine if a relationship exists between fungistasis and disease incidence. There was no significant soil effect on CPB mortality, but log-probit regressions of dose-mortality against fungistasis levels revealed a significant trend of increasing LD50 values with increasing fungistasis. There was significantly more sporulation of B. bassiana on inoculated CPB pupae incubated in Rhode Island soils than in Michigan soils. © 1991.