Sprayed barriers of diflubenzuron (ULV) as a control technique against marching hopper bands of migratory locust Locusta migratoria capito (Sauss.) (Orthoptera: Acrididae) in Southern Madagascar

Abstract

Diflubenzuron was applied to vegetation using handheld Micro-Ulva spinning disc sprayers in barriers. Volume application rate was 0.8 l ha-1 in the barriers and mass application rate was 93.7 g a.i. ha-1 in the barrier, equivalent to 7.8 g a.i. ha-1 overall. A total of 8 barriers, 50 m wide, were sprayed with a 600 m barrier spacing. The approximately square plot of 1649 ha was infested with transiens phase marching hopper hands of Locusta migratoria capito (Sauss.) (Orthoptera: Acrididae). The effects on hopper bands within the plot were monitored and compared with bands from an untreated control plot. Observations of hopper density, hopper band area, age structure and band displacement were made daily. Diflubenzuron effects were observed within 3 days of spraying. All hopper bands in the treated plot and all nymphal stages were affected. In both treated and control plots population decreases were observed in all monitored bands. The decrease in hopper bands in the treated plot was mainly due to diflubenzuron effects whereas that in the control was due to dispersal and some natural mortality. Hopper bands in the treated plot showed decreased displacement rates especially when encountering diflubenzuron barriers. Quadrat studies of locust populations in the plots showed a marked reduction in locust numbers in the treated plot that was significantly different from the control