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 wa s used to apply Metarhizium flavoviride isolate IMI 330189 to brown lo cust (Locustana pardalina) populations (mostly Vth instar nymphs) in t he 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 setti ng 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.Sample s consisted of insects kept in cages under field conditions and sectio ns of hopper bands maintained in open-topped field enclosures. All tre ated bands showed significantly greater mortality than the controls, w ith up to 98% mortality in samples maintained in enclosures after 3 we eks. Mortality in caged samples was often faster than with hoppers mai ntained in field enclosures. The relative efficacy of the various meth ods 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 impacti on, affected primarily by the wind-speed at the time of spraying. (C) 1997 Elsevier Science Ltd.