Metarhizium spp. isolates from madagascar: Morphology and effect of high temperature on growth and infectivity to the migratory locust,Locusta migratoria

Five strains ofMetarhizium anisopliae (Metsch.) Sorokin and one strain ofMetarhizium flavoviride Gams &; Rozsypal originally isolated in Madagascar were studied. Measurements of conidia and, for the first time, also of blastospores produced in a liquid medium were used for species and variety determination. Blastospores ofM. flavoviride were more homogenous in their size than those ofM. anisopliae. Growth at high temperatures between 25° and 40°C showed that 4 isolates ofM. anisopliae grew at 36°C andM. flavoviride grew at 38°C. Using alternating day/night temperatures (8/16 h) the three strains tested could also tolerate 40°/25°C. In bioassays, fiveMetarhizium spp. isolates were tested against third and fourth instar larvae ofLocusta migratoria (L.) at two alternating day/night temperatures of 30°/25°C and 36°/25°C. In the cooler regime, all strains caused a mortality of 50% within 5.9 to 8.5 days (median lethal time), while in the 36°/25°C treatment only the thermophilicM. flavoviride and oneM. anisopliae strain isolated from a soil sample gave comparable results with median lethal times of 6.8 and 7.3 days, respectively.