Field Infection ofZonocerus variegatusfollowing application of an oil‐based formulation ofMetarhizium flavovirideconidia

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Abstract
Conidia of Metarhizium flavoviride grown in diphasic culture with sporulation on rice, were extracted in kerosene and formulated with peanut oil. The formulation led to high mortality when applied to field populations of Zonocerus variegatus; between 70 and 95% of insects in samples collected from the field 0, 3 or 7 days after spraying died. Sporulation of M. flavoviride was observed in 70–80% of the dead‐treated insects, which compares favourably with results obtained in laboratory bioassays. Many dead Z. variegatus, some with internal sporulation, were found in shaded niches and oviposition sites in the treated plots. No sporulation was observed in samples collected prior to application, and both sporulation and mortality differed significantly between control and treated plots. Some infections were observed in insects collected 16 and 23 days after treatment; these late infections may be a consequence of contact with spores surviving in the environment.