INFECTIVITY OF PROPAGULES OF PAECILOMYCES-FUMOSOROSEUS DURING IN-VITRO DEVELOPMENT TO SPODOPTERA-FRUGIPERDA

Ungerminated aerial conidia and four different stages of the growth of Paecilomyces fumosoroseus in submerged culture consisting of swollen conidia, germinated conidia with either one or two germ tubes and hyphal bodies, were assayed for infectivity to 0- to 18-hr-old first-instar larvae of Spodoptera frugiperda at 25 +/- 1 degrees C. Germinated conidia and hyphal bodies were more aggressive than ungerminated conidia. Mortality rates in the first larval instar were 29% for larvae contaminated with inactive conidia, 43-49% for larvae treated with germinated conidia, and 61% for larvae treated with hyphal bodies at a dosage of 3 x 10(4) propagules cm(-2). The infective process varied with the type of propagules, with LT(50)s ranging from 4.0 to 3.1 days. Moreover, the pathogenic activity of the vegetative forms appeared higher than those of the initial ungerminated inoculum under unfavorable conditions such as reduced fungal dosage (3 x 10(3) propagules cm(-2)), premolt larvae (35-40 hr old), and higher temperature (28 +/- 1 degrees C). (C) 1994 Academie Press, Inc.