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

Abstract

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 × 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 °. 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.