Biochar-Derived Smoke Waters Affect Bactrocera oleae Behavior and Control the Olive Fruit Fly under Field Conditions

Bactrocera oleae is the key pest of olive production. Several attempts have been carried out over time to control it using biological solutions but with results rarely comparable to those obtained with chemical applications. The purpose of this work was to identify and test new compounds from samples of various Smoke Waters (SWs) for their effect on the fly, and given their low impact on the environment. SWs obtained from different feedstocks were used in in vitro and open field applications. SWs were shown to alter B. oleae fitness, acting on its microbiome, particularly on the presence and activity of the primary endosymbiont "Ca. Erwinia dacicola", and also to affect the behavior of the adult flies, altering the attractiveness of the drupes susceptible to attack. The effects recorded were concentration-dependent and varied among repulsion, up to 87% towards females, indecision, up to 70% towards males, and attraction, comparable to fresh green olives, based on the starting materials. These responses were confirmed in electroantennography trials and during two-years of field trials carried out in South and Central Italy. Gas Chromatography-Mass Spectrometry highlighted the presence of compounds such as guaiacol and hydroquinone as potentially important for the observed activity. Principal Component Analyses confirmed the proximity among SWs obtained from similar feedstocks. In controlled conditions, females appear to be more sensitive to the SW treatments. Field trials have shown how the effects of SWs can lead depression of infestation levels obtainable with other well-known compounds, such as kaolin clay and isopropyl-myristate (repulsive), or pheromones (attractive).