• stored foodstuff
• meat
• insect pest
• hydrolate
• essential oil
• chitosan
• botanicals
• vegetable oil

It is estimated that, in the whole world, are present 10 quintillion living insect specimens at any time. Among the almost one million species of insects already described, only 1 to 3% is considered a pest by humans because harmful to themselves or their animals, plants, and buildings. With the advent of synthetic insecticides around the 1940s, the control of insect pests became highly effective, with a substantial reduction of infectious diseases for humans and animals and crop yields almost doubled. However, the abuse of such chemical products with massive and continuous applications over time has led to catastrophic drawbacks: toxicity on mammals, deleterious effects on the environment, soil, groundwater, and air pollution, development of resistance in the treated species, adverse effects on non-targets, presence of residues on food, bioaccumulation, and biomagnification in food chains. In Europe, the urgent need for eco-friendly insecticidal agents has been first stimulated by Directive 2009/128/EC on the sustainable use of pesticides and later by the Horizon 2020 research and innovation funding programme and the current 2030 Agenda. Botanicals, meaning all the bioactive compounds, extracts, and mixtures of vegetal origin that serve as insecticides, repellents, nematicides, bactericides, fungicides, and herbicides, seem to be promising candidates.
Essential oils (EOs) are complex and heterogeneous mixtures of secondary metabolites extracted from the so-called aromatic plants. From the vast body of literature, EOs appear to have low (or no) toxicity on vertebrates and non-target species, multiple modes of action that prevent the development of resistance, low impact on the environment, and fast decomposability. On the other hand, EOs have some limits that are slowing down their expected application in practice. The EOs’ composition is highly variable due to extrinsic and intrinsic factors, and they have distinctive odours that need to be characterised from a sensorial perspective before suggesting a specific application, are highly volatile and easily degradable, so they should be included in matrices that enhance and prolong their bioactivity, and their extraction through hydro- and steam distillation generate a significant amount of water that condenses in the decanter at the end of the processes (called hydrolate) and the solid residue of the spent vegetal material as unexploited by-products. This thesis addresses certain limits of botanicals and proposes some possible solutions through the analyses of data obtained from several entomological trials.
1. Chemotypes are subspecies of plants that are morphologically equal but produce different quantities and types of secondary metabolites, therefore of EOs. Three EOs extracted from different chemotypes of Origanum vulgare L. (Lamiaceae), namely carvacrol, thymol/p-cymene, and thymol/γ-terpinene, are tested on the blue blowfly Calliphora vomitoria (L.) (Diptera: Calliphoridae) by contact on adults and eggs and as repellents on gravid females of the same species. The results are dose or concentration-dependent but also deeply related to the chemotype, with an overall better performance by the thymol/γ-terpinene chemotype. The chemotypes phenomenon, more common in Lamiaceae aromatic plants, should be always considered when working with EOs.
2. The odour of each EO is distinctive and can be perceived by mammals and insects through different organs and with different reactions (attractiveness vs repellence). Two EOs extracted from Ecuadorian plants traditionally appreciated for their pleasant smells, namely Aloysia citrodora Palau (Verbenaceae) and Bursera graveolens (Kunth) Triana & Planch. (Burseraceae), are characterised by expert sensorial analysts and tested on C. vomitoria adults (by contact, fumigation, ingestion, and behaviourally) and eggs (by contact). The results are, as expected, dose or concentration-dependent and change according to the EO. Remarkably, A. citrodora EO is a valid insecticide by contact and repellent towards the blowfly and has a favourable olfactory profile for humans (sweet and lemony scents) that makes it a good candidate for the formulation of a repellent and toxic indoor and outdoor environmental spray.
3. A promising matrix for EOs formulation is chitosan (CH), a renewable and biodegradable aminopolysaccharide chemically obtained from chitin of various origins. Two EOs extracted from aromatic plants traditionally used to season meat dishes, namely Laurus nobilis L. (Lauraceae) and Piper nigrum L. (Piperaceae), are selected among others by trained panellists and used, formulated with CH, to protect minced beef meat against the oviposition by C. vomitoria. The significant repellence exerted by the proposed treatments is associated with meat organoleptic qualities preservation and prolonged shelf-life, too (evaluation of meat colour, dehydration, and lipid peroxidation during 7 days of cold storage).
4. The hydro-distillation of flowers and stems of Lavandula × intermedia Emeric ex Loisel. (Lamiaceae) gives a minor fraction of EO and a conspicuous amount of hydrolate and spent straws. Based on the composition of the hydrolates, rich in linalool, 1,8-cineole, and camphor, known as insect repellents and germination inhibitors, we test them as repellents towards the flour beetle Tribolium confusum J. du Val (Coleoptera: Tenebrionidae) and against the germination of Raphanus sativus L. (Brassicaceae) seeds. The results show that the flowers hydrolate has both the expected effects, so it should not be considered only a mere waste of the EO extraction process but one of its main products.
5. Another remarkable group of botanicals is represented by vegetable oils from various seeds and fruits, like peanut Arachis hypogaea L. (Fabaceae) oil, used as sustainable protectors of stored grains. We test the toxicity of a crude peanut oil (not refined) and four rectified peanut oils (one through the chemical, traditional method and three with degumming enzymes with hydrolytic activity on fatty acids) on the maize weevil Sitophilus zeamais Motsch. (Coleoptera: Curculionidae). All the proposed peanut oils are effective, and the enzymatic degumming is a greener procedure, as it requires lower amounts of chemical solvents to work, gives an increase in oil yield, and a decrease in the weight and volume of the remaining gums (phospholipids) that are easier and cheaper to dispose of.
In conclusion, research about the application of botanicals to control harmful insects, under laboratory conditions and in the field, is still much needed even after more than 40 years from the beginning of the interest in vegetal substances as possible pesticides. To achieve the expected diffusion of botanicals are certainly needed stable formulations, standardised compositions, and the involvement of entomologists, chemists, sensorial analysts, food technologists, and many other professionals in a multidisciplinary and shared effort.