Growth and sporulation of entomopathogenic Beauveria bassiana, Metarhizium anisopliae, Isaria farinosa and Isaria fumosorosea strains in relation to water activity and temperature interactions

Abstract

This study examined six strains of Beauveria bassiana s.l. and Isaria farinosa, one strain of Isaria fumosorosea and five strains of Metarhizium anisopliae s.l. to identify the ability for (1) growth and (2) sporulation under interacting environmental factors of water activity (aw) and temperature stress. Growth on Sabouraud Dextrose Agar (SDA; water activity, aw = 0.995) or SDA modified with glycerol to 0.98, 0.96 and 0.94 aw was measured at four different temperatures (25, 30, 35 and 37°C). All M. anisopliae strains grew at 25–35°C and 0.995 aw while only two strains tolerated extreme water stress at 0.94 aw.Three strains of B. bassiana were able to grow at 25–37°C and 0.995 aw. Only one strain of I. farinosa was able to grow at 25–37°C and 0.995 aw. Aw and temperature interactions resulted in different strain-dependent responses, in terms of growth and sporulation. Only one strain of I. farinosa and three of M. anisopliae grew at 0.94 aw and none of the B. bassiana strains tolerated such water stress. At 0.96 and 0.94 aw and 35–37°C, sporulation by all the strains of the three species were significantly affected. Under elevated temperatures and drought stress, very few of these strains of entomopathogenic fungi are able to grow and sporulate. Indeed, the B. bassiana strains were unable to tolerate the extreme conditions examined. Resilience to such abiotic interactions is critical for selecting strains for formulations. Tolerance to water and temperature stress could be good criteria for selection of strains with secondary spread potential for use as part of an integrated pest management system where secondary cycling may be important, especially in sub-tropical and tropical environments.