Aldehyde-containing clays and zeolites: a sustainable approach in the control of olive fruit fly, Bactrocera oleae

The implementation of innovative and environment-friendly control methods against the olive fruit fly, Bactrocera oleae, has attracted an ever-growing attention, especially after 2014, 2016 and 2019 when the Italian olive oil production suffered from qualitative and quantitative losses. In this aim, two series of solids were prepared: 1) copper(II)-exchanged clinoptilolite zeolites and 2) organically modified montmorillonite clays, over which aliphatic aldehydes, [E]-hex-2-enal; [E]-hept-2-enal, n-hexanal; n-heptanal, have been deposited. The final goal is to set up a composite oxidic material capable to host a bioactive compound able to effectively disrupt the host-plant selection process of B. oleae adults featuring a targeted and constant release for a long-term treatment of the olive fruits. A maximum aldehyde loading of 4.7 wt.% and 13.5 wt.% was obtained for aldehyde/bentonite (C6-Ben, C7-Ben) and aldehyde/zeolite (C6-Zeo, C7-Zeo), respectively. The solids were fully characterized by physico-chemical analysis and a specific adsorption of the aldehyde into the interlayer space of the clay was evidenced (Figure 1 a). Tests for the evaluation of the release capability showed a smooth aldehyde desorption up to 40 days, under ambient conditions. Large kilogram-scale batches of the aldehyde/bentonite material were tested under real conditions, in an open-field trial on an olive tree orchard in Southern Tuscany (Figure 1 b). Extremely promising results were obtained with Cu-zeolite and with both aldehyde-containing bentonite-like montmorillonite clays, in terms of reduction of both fly infestation (up to 98 % reduction) and damages on the olive fruit. These materials proved to be easily prepared, cost effective, environment-friendly, stable to rainwater leaching and led to a remarkable diminution in the use of bioactive species (and copper-containing ingredients) for on-field applications.