Refreshing bait spots in an olive orchard for the control of Bactrocera oleae (Diptera: Tephritidae)

Key to the success of the ground bait spray application method ('attract and kill') against Bactrocera oleae (Gmelin) is the long-term maintenance of the attractiveness of the trophic attractant as well as the toxicity of the active ingredient included in a bait spot. Large-scale field trials were conducted in olive orchards on Crete to estimate the quantity of alpha-cypermethrin applied as a bait spot on olive leaves as well as lab experiments to evaluate its residual effectiveness against the fly over time. Alpha-cypermethrin remained effective in olive tree canopies for at least 2 months (residues of alpha-cypermethrin on olive leaves were detected 7 days after the first and second bait spray applications and ranged from 5 to 7 and 16 to 19 mg/kg, respectively, as indicated by GC-MS/MS analysis, while the recorded adult mortality was >55% for at least 20 weeks following spray application). Moreover, additional protein-only sprays to specific parts of the olive canopy that had been previously sprayed with a bait spraying solution (alpha-cypermethrin plus hydrolysed protein at 75% w/w) significantly reduced olive fruit fly captures in treated plots compared to the captures recorded in plots with the classical bait spray. The percentages of live infestation of B. oleae were very low (<2%) and did not differ significantly between the two tested practices. The benefits of the reduced use of pesticides in the management of this pest are discussed.