Natural Enemies and Pest Control

A number of invertebrates, mainly Nematods, Mites and Insects, affect directly or indirectly the human economy. Some of these may damage, according to ecological conditions and their evolutive adaptations, the human health and that of domestic and wild animals; other offend our sense of aesthetics or cause severe economic damage to cultivated plants. A spectrum of types of damage, sometimes very different between them, involves the latter to the point of hindering the formulation of a general concept of harmfulness, and forcing to examine the phenomenon from an anthropocentric point of view. Phytophagous species living on cultivated plants and/or their products are commonly referred as pests; their damage induces a deleterious effect on the physiology of the host plant and/or on the quality and quantity of their products, and the resulting loss can be defined as the amount of measurable economic impact negative in terms of utility or production of plant species attacked. The relationship between pests and cultivated plants can be approached from various points, e.g. taxonomic, morphological, bio-ecological, economic, etc.Usually, the breaks of pest populations are associated with the modifications of the ecological stability of ecosystems, due to action of ecological perturbations able to influence different factors, among which the populations of natural enemies of pests. To all this is added the introduction of pests from other areas of origin, that are able to spread rapidly with serious consequences for the cultivated plants and for biodiversity. In some cases the pest is considered low-pest density as the species vectors of diseases of plants, animals and humans. The knowledge of the ecological factors that govern the ecosystems helps then to rationalize the pest control, highlighting the most suitable means and strategies, including the priority action of natural enemies, indigenous and/or introduced.The use of these natural resources allows to realize the biological control of pests, a strategy historically known from centuries in different countries (e.g. the China, the Ancient Egypt, etc.), but technically established itself during the latter century when started the scientific assessment of its economic and eco-toxicological benefits. The relationship between the pests and their natural enemies (and their possible application in the field) involves various ecological factors. Of these, the flows of matter and energy within the ecosystems, their stability and the perturbations that may occur within them play a key role. Understand these factors make then possible to examine the role of natural enemies in the ecosystems and their possible use in the field. Unfortunately, the purpose of the book, and the lack of space does not allow to operate any reminder of these concepts and suggests the interested reader to consult specific texts of applied Ecology to production systems. Here we simply treat the natural enemies of pests and their implications, including their contribution in the organic farming.