Aerial spray trials against brown locust (Locustana pardalina, Walker) nymphs in South Africa using oil-based formulations of Metarhizium flavoviride

A large micro-light aircraft fitted with Micronair AU7000 atomisers was used to apply Metarhizium flavoviride isolate IMI 330189 to brown locust (Locustana pardalina) populations (mostly Vth instar nymphs) in the Richmond District of the Karoo in South Africa. Dry conidial powder was formulated in a paraffinic oil mixture to apply approximately 2.0 x 10(12) conidia per hectare with volume application rates of 1.0 and 2.5 l/ha. Three different droplet size spectra were produced by setting the pitch of the atomiser turbine blades to 25, 35 and 45 degrees. A total of ten hopper bands were treated on three separate days. Samples consisted of insects kept in cages under field conditions and sections of hopper bands maintained in open-topped field enclosures. All treated bands showed significantly greater mortality than the controls, with up to 98% mortality in samples maintained in enclosures after 3 weeks. Mortality in caged samples was often faster than with hoppers maintained in field enclosures. The relative efficacy of the various methods of aerial application will need confirmation in further trials; a volume rate of 2.5 l/ha appeared to give more consistent results than 1 l/ha applications. Mortality was probably related to droplet impaction, affected primarily by the wind-speed at the time of spraying. (C) 1997 Elsevier Science Ltd.