The effects of duration of development and drying regime on the longevity of conidia of Metarhizium flavoviride

Conidia of the entomopathogenic Metarhizium flavoviride were harvested 8, 10, 12 or 15 d after inoculation at 25 °C and then (as conidiated rice) dried rapidly (10-12% r.h. and 17-20°for 17 h to about 15-22% moisture content) or slowly (50-60% r.h. and 27°for 5 d to about 27-32% moisture content initially). The subsequent survival of these conidia in air-dry storage at 50°with 8·1% moisture content was then assessed. Conidia longevity (assessed by the duration of storage until conidia viability was reduced to 50%, p₅₀) was maximal when conidia were harvested 10 d after inoculation, and was much greater following slow rather than rapid drying. The substantial beneficial effect of slow desiccation to subsequent conidia survival is consistent with that detected in other propagules in anhydrous biology, and is also of considerable practical utility for the biological control of insects by entomopathogenic fungi.