INFLUENCE OF TEMPERATURE ON INVITRO GROWTH OF ENTOMOPATHOGENIC HYPHOMYCETES

Thirty-one isolates of 6 entomopathogenic hyphomycetes, Beauveria bassiana (Balsamo) Vuillemin, B brongniartii (= tenella) (Saccardo) Petch, Metarhizium anisopliae (Metschnikoff) Sorokin, M flavoviride Gams et Rozsypal, Nomuraea rileyi (Farlow) Samsom and Paecilomyces fumosoroseus (Wize) Brown et Smith, were grown in vitro to determine growth rates and ranges of growth at 10 temperatures from 8 to 37-degrees-C in the dark. Radial growth of surface colonies on semisynthetic nutrient agar was recorded by daily measurement of 2 cardinal diameters. Because radial measurements (from day 3 to 12) of surface colonies for each temperature fit a linear model (y = vt+b), growth rates (v in mm x day-1) were used as the main growth parameter to evaluate the influence of temperature. The fungal isolates under study exhibited a wide diversity of responses to temperature according to their provenance. Isolates originating from tropical areas showed a remarkable growth at 35-degrees-C (eg, M anisopliae isolates). By contrast, isolates originating from soil-inhabiting insects of temperate areas (eg B brongniartii isolates) exhibited high growth rates at 8-degrees-C. However, the optimal growth was found at 25-degrees-C for 26 isolates. Upper temperature limits of growth varied from 28-37-degrees-C according to both fungal species and isolates. M anisopliae isolates exhibited an almost ideal combination of high growth rates and in particular a wide temperature range (8-11-degrees to 35-37-degrees-C); only one B bassiana isolate showed similar responses to temperature stimuli. Although the optimal temperature for fungal growth is not necessarily the same as that for fungal infection in insects, temperature ranges established according to in vitro growth data might be used for selecting fungal candidates for microbial control.