Investigating a replacement for malathion in bait sprays for fruit fly control in South African citrus orchards

Abstract

The use of the organophosphate malathion (mercaptothion) in protein bait sprays for fruit fly (Diptera: Tephritidae) control in South African citrus orchards will slowly phase out due to lower tolerances of residues of this insecticide on fruit destined for export markets. As such, a replacement for malathion is being sought. In this study, efficacy of six insecticides: abamectin, alpha-cypermethrin, fipronil, imidacloprid, spinosad and tartar emetic, in combination with HymLure (a protein based attractant), was determined in laboratory assays on female Mediterranean fruit flies, Ceratitis capitata Wiedemann. Three concentrations of HymLure (0.8%, 2% and 10%) were tested with five concentrations of each insecticide. Thereafter the efficacy of the most promising attractant–insecticide combination was determined and compared in the laboratory and in a citrus orchard to standard HymLure–malathion (mixture of 0.8% HymLure and malathion at 875 ppm, diluted in water) and GF-120 (5%, diluted in water) treatments for C. capitata and Ceratitis rosa Karsch (Natal fly). Among the insecticides tested, spinosad was found to induce the highest fly mortality in a shorter time over the whole range of concentrations tested, with mortality reaching above 80% after 24 h when combined with a solution of either 2% HymLure or 10% HymLure. Fipronil, tartar emetic and imidacloprid did not act as fast but were also effective, especially when combined with higher concentrations of HymLure. A mixture of 2% HymLure and spinosad at 48 ppm was found to be effective against both C. capitata and C. rosa in both laboratory and field tests and could therefore be recommended as a replacement for malathion-based bait sprays.