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

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.

► Efficacy of 6 insecticides in combination with a protein hydrolysate was evaluated.
► Spinosad induced the highest fly mortality in combination with the protein bait.
► A mixture of HymLure and spinosad was found to be effective.