PATHOGENICITY OF THE ENTOMOGENOUS, HYPHOMYCETE FUNGUS, METARHIZIUM-ANISOPLIAE AGAINST THE CHRYSOMELID BEETLES PSYLLIODES-CHRYSOCEPHALA AND PHAEDON-COCHLEARIAE

Susceptibility of the mustard beetle (Phaedon cochleariae) and the cabbage stem flea beetle (Psylliodes chrysocephala) to six isolates of the entomogenous, hyphomycete fungus, Metarhizium anisopliae, was investigated. A further six isolates were assayed against P. cochleariae only. The isolates originated from hosts of various insect orders. Five of the six isolates tested against P. chrysocephala and P. cochleariae were infective for both species whereas one isolate, V107, was non-pathogenic to both. The level of virulence of different M. anisopliae isolates for these chrysomelid beetles varied considerably. Isolates V90 and V93 were highly virulent to P. chrysocephala and P. cochleariae respectively but were significantly less virulent against the alternate host species. The LT50 of isolate V90 for P. chrysocephala was 7 days at 4 x 10(7) conidia/ml and its LC50 value was 16 x 10(5) conidia/ml. The LT50 of V93 for P. cochleariae was approximately 8 days at 4 x 10(8) conidia/ml and its LC50 value was 3 x 10(7) conidia/ml. Following inoculation, germinating conidia of all isolates produced appressoria on the cuticular surface of both hosts suggesting that specificity is determined at later stages of infection.