A comparison of the virulence, stability and cell-wall-surface characteristics of three spore types produced by the entomopathogenic fungus Beauveria bassiana

Abstract

Beauveria bassiana can produce three spore types; aerial conidia, submerged conidia and blastospores. We have examined the spore surface characteristics (hydrophobicity and cell-wall surface lectins), thermal inactivation and the virulence towards the migratory grasshopper, Melanoplus sanguinipes, of each of the three spore types. The hydrophobicities of the aerial and submerged conidia were quite similar. Blastospores were less hydrophobic than either of the two types of conidia. Hydrophobic interactions are thought to play a significant role in attachment of the spore to the host organism. However, the less hydrophobic blastospores were slightly more virulent (LT50 of 6.50 days) when compared to the aerial and submerged conidia (7.12 and 7.24 days), respectively. The lectin-binding characteristics of the aerial and submerged conidia were very similar but differed from that of blastospores. Growth of blastospores on a variety of carbohydrates did not affect their lectin-binding characteristics. Spore viability measurements showed that aerial and submerged conidia retained their viability for a longer period than blastospores. The similarity in hydrophobicity, stability, virulence and lectin-binding of aerial and submerged conidia make the latter an ideal candidate for mycoinsecticide production since they can be recovered after growth on inexpensive substrates.