Water stress and harmful insects in agri-forest ecosystems

Present knowledge on ecological services supplied by insects to natural terrestrial ecosystems, allow us to identify many homeostatic mechanisms regulating biological balance as well as life perpetuation of the said ecosystems; at the same time, that knowledge represents a sound referring point to understanding how those mechanisms do work so as to manage them in the anthropized ecosystems (i.e., agriculture and forests), and especially in order to identify in the latter the natural meaning of the so called insect outbreaks, so as to forecast and possibly prevent them; as well as, when needed, to conceive and formulate efficient control strategies having minimal environmental impact. Water factor is crucial with genesis, configuration and conservation of a terrestrial ecosystem (both natural or anthropized) as a whole or in its individual components, but especially concerning plant life as well as plant interactions with phytophagous invertebrates, mainly insects. Insect-plant trophic interactions are principally influenced by the water conditions in the ecosystem, and the impact of phytophagous insects on crops is markedly affected. Extremely severe water stress, especially if prolonged, prevent insect life just like plant’s life but a moderate and not so prolonged water stress, while depressing plant vigour, paradoxically can improve development and multiplication of phytophagous arthropods, with severe consequences on woody plants especially, and forest trees markedly.