Residual attractiveness of various bait spray solutions to Bactrocera oleae

- Protein mixed with alpha-cypermethrin exhibited the highest attractiveness.
- pH values of bait spray solutions over time were associated with fly catches.
- The residual attractiveness of bait spraying solutions on foliage is limited.

Effective insecticidal bait formulations ought to induce high levels of attraction and stimulate flies to ingest a lethal dose of the toxicant upon feeding or contact. The key to the effectiveness of such baits is the amount of time that the bait remains attractive to adult flies after spray application. Solutions of trophical attractants of Bactrocera oleae (two formulations of hydrolysed proteins at 55% and 75% w/w) mixed with various insecticides (alpha-cypermethrin, lambda-cyhalothrin and dimethoate) and a spinosad solution, applied either in McPhail traps or sprayed in olive foliage (except lambda-cyhalothrin), were tested for their attractiveness over time during two periods in successive summers. The results indicated that among all bait spraying solutions tested against B. oleae, the highest catches were recorded with both protein solutions of alpha-cypermethrin; its capture rate ranged from 7.6 to 10.5 olive fruit flies/trap/solution age (seven measurements were made when the trap solution was changed at 3, 7, 10, 14, 17, 20 and 24 days after its preparation). A three-day-old solution of any protein mixed with alpha-cypermethrin was significantly more attractive to olive fruit flies (at least three times) compared with the solutions at other ages, as indicated by the capture of flies in the McPhail traps. No differences were observed among solution ages for dimethoate solutions or spinosad solutions (less than 6 olive fruit flies/trap/week). When olive foliage was sprayed with the solutions under field conditions, they attracted approximately 0.3-1.5 adults per day for a 10-day period. The highest number of flies was recorded on both proteins combined with or without alpha-cypermethrin solution, as indicated by the catches on sticky transparent panels. Finally, changes in the pH values of the aforementioned solutions over time were associated with increased fly catches.