FIELD INFECTION OF ZONOCERUS-VARIEGATUS FOLLOWING APPLICATION OF AN OIL-BASED FORMULATION OF METARHIZIUM-FLAVOVIRIDE CONIDIA

Conidia of Metarhizium flavoviride grown in diphasic culture with spor ulation on rice, were extracted in kerosene and formulated with peanut oil. The formulation led to high mortality when applied to field popu lations of Zonocerus variegatus; between 70 and 95% of insects in samp les collected from the field 0, 3 or 7 days after spraying died. Sporu lation of M. flavoviride was observed in 70-80% of the dead-treated in sects, which compares favourably with results obtained in laboratory b ioassays. Many dead Z. variegatus, some with internal sporulation, wer e found in shaded niches and oviposition sites in the treated plots. N o sporulation was observed in samples collected prior to application, and both sporulation and mortality differed significantly between cont rol and treated plots. Some infections were observed in insects collec ted 16 and 23 days after treatment, these late infections may be a con sequence of contact with spores surviving in the environment.