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 AU 7000 atomisers was used to apply Metarhizium flavoviride isolate IMI 330189 to Locustana pardalina populations (mostly 5th-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 × 1012 conidia per hectare with volume application rates of 1.0 and 2.5 litres/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 10 hopper bands was treated on 3 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. A volume rate of 2.5 litres/ha appeared to give more consistent results than 1 litre/ha applications. Mortality was probably related to droplet impaction, affected primarily by the wind-speed at the time of spraying.