Biological control of whiteflies on protected vegetable crops in Sicily (south Italy): from illusions to reality

In Sicily about 4,000 hectares are planted with vegetables under greenhouses, being the widest Italian area for this production. Tomato is the most important crop, with an almost 200,000-ton production, followed by zucchini, with over 45,000 tons; eggplant and bell pepper, producing almost 40,000 and 27,000 tons respectively, are also important crops. Various pests threaten vegetable production in this area and whiteflies, especially Bemisia tabaci, occupy a prominent role, above all for the viruses they transmit. Biological control, although giving valid results against whiteflies, does not establish satisfactorily in this productive area. From a survey conducted within the European project "Virtigation" (https://www.virtigation.eu/), it has been noted how only about 32% of farms uses natural enemies (predators or parasitoids) to control whiteflies, regardless of the age and educational attainment of the holder (with almost 45% of the growers who adopt biological control being 40-65 years old and having a low educational level). Predators have the clear prevalence among natural enemies used in Sicily for biological control of whiteflies, especially with Nesidiocoris tenuis (used by more than 70% of the farmers adopting augmentative releases of natural enemies), followed by Macrolophus pygmaeus (almost 55%) and the phytoseiid mite Amblyseius swirskii (less than 30%). Interestingly, predatory Myrid bugs are also used by farms which do not adhere to any organic or integrated production disciplinary. The use of parasitoids is limited, with Encarsia formosa used only by little more than 25% of the farmers, and Eretmocerus eremicus used by less than 10%. On the basis of this survey, an attempt is made to analyse possible reasons for such a limited diffusion of biological control in a production area of such extent and importance, hypothesizing possible solutions for a promotion of eco-sustainable techniques for pest control in the local protected vegetable crops.