Centuries of botanicals in arthropod pest control, but something is still missing

Botanical pesticides, derived from plant tissues variously extracted or distilled, are certainly not a recent discovery. Indeed, for centuries they have been part of the arsenal available to humans to defend themselves and their animals and crops against insect and mite pests. Their use began to decline around the 1940s, when they were replaced by synthetic pesticides, which are undoubtedly effective but, concurrently, more toxic to the non-target species, pollutant for the soil, groundwater, and air, and cause of the development of resistance when misused. What we are now experiencing is a renewed interest in botanicals as a possible greener, ecofriendly, and sustainable alternative to most of the pesticides of chemical origin. Currently, azadirachtin, pyrethrum (both of which are broadspectrum insecticides and repellents), and some plant primary metabolites (such as formic and oxalic acids used as miticides in beekeeping) account for the largest share of the botanical pesticide market. An outstanding potential in arthropod pest management has also been shown by the essential oils, although their applications in the field and under operational conditions are currently limited. Essential oils are heterogeneous mixtures of secondary metabolites obtained from aromatic plants and are valued for their low toxicity to vertebrates, high biodegradability, and multiple modes of action that likely avoid the development of resistance. However, what is still missing are proper chemical characterizations (some plant species show chemotypes with different compositions), sensory evaluations (essential oils have specific odours and flavours that should be matched with the intended applications like as environmental sprays, skin treatments, or food protectants), and formulations within stabilising matrices (e.g., chitosan, cellulose, exopolysaccharides) or through microand nano-technologies (e.g., encapsulation, sonication). To cope with such shortcomings, a joint effort by entomologists, chemists, producers, sensory analysts, food technologists, engineers, and many other professionals is needed as soon as possible.