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 hyph al bodies, were assayed for infectivity to 0- to 18-hr-old first-insta r larvae of Spodoptera frugiperda at 25 +/- 1 degrees C. Germinated co nidia and hyphal bodies were more aggressive than ungerminated conidia . Mortality rates in the first larval instar were 29% for larvae conta minated with inactive conidia, 43-49% for larvae treated with germinat ed 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. Moreove r, the pathogenic activity of the vegetative forms appeared higher tha n those of the initial ungerminated inoculum under unfavorable conditi ons such as reduced fungal dosage (3 x 10(3) propagules cm(-2)), premo lt larvae (35-40 hr old), and higher temperature (28 +/- 1 degrees C). (C) 1994 Academie Press, Inc.