To push, pull or push-pull? A behavioural strategy for protecting small tomato plots from tephritid fruit flies.
The protective effects of protein bait spays and oil emulsion sprays against fruit flies (Bactrocera tryoni (Froggatt)) were compared in an experiment with a simple split plot design using tomatoes (Solanum lycopersicum L.) of two varieties. The sprays were then used in a second experimental design based on the 'push-pull' technique that would be relevant to home gardens and village horticulture. Each replicate of each treatment in each of two experiments was represented by a small group of fruiting tomato plants (that represented a small crop in a real garden to be protected by the technique). These were surrounded by other tomato plants (that were stripped of fruit) or by weeds (that represented other food plants or weeds in a real garden). Each category of plant was given either no treatment or imparted with a 'push' or a 'pull' stimulus with a bait spray or an oil spray to act on foraging fruit flies. A simultaneous comparison of all nine possible combinations of these treatments revealed that oil spray applied only to the central plants or to both the central and surrounding plants were two of the three most effective treatments for preventing fruit damage by fruit flies. Bait spray on its own was not always effective and, when paired with oil spray, was no more successful than no treatment paired with oil spray. Another experiment, restricted to combinations of oil spray and no spray, confirmed that plants were best protected by direct application of oil spray and that spraying surrounding plants as well was no better and that spraying surrounding plants alone was worse. These results were related to the small size of each 'crop' and known aspects of fruit fly behaviour.