The germination of oil-formulated conidia of the insect pathogen, Metarhizium anisopliae

Conidia of Metarhizium anisopliae need water activity (A(w)) > 0.98 for ger mination irrespective of whether they are formulated in an aqueous or oil c arrier. The presence of nutrients in the carriers or culture medium acceler ated germination but did not increase the range of A(w) (or humidities) ove r which conidia could germinate. Insect extract stimulated more conidia to germinate than yeast extract. Oils appeared to extract fungistatic and stim ulatory compounds from the insect cuticle. The ratio of these compounds dep ends on both the insect species and the carrier. Conidia of M. anisopliae f ormulated in oils were observed with SEM to flow over the surface of insect and plant cuticles. The conidia were probably deposited at sites which are conducive for germination and infection and consequently increased the ove rall mortality of insects. In contrast, aqueous formulations of conidia rem ain as drops on the leaf surface immediately after application with a pipet teman or sprayer.