ABSTRACT
Parasitoids are important regulators of insect populations, and they stand out as the main group of natural enemies in agricultural systems. Insect parasitoids are spread over a number of insect orders, but the adaptations to the parasitic way of life are more diverse and abundant in the Hymenoptera (Askew 1973, Vinson and Iwantsch 1980a, Pennacchio and Strand 2006). The efficiency of parasitic Hymenoptera in host exploitation is due to their long evolutionary process for overcoming the diverse restrictions imposed by the host and its habitat. The origin of parasitism in the Hymenoptera is still under debate, with some data indicating parasitism appeared as a way of life as early as the beginning of the Jurassic, around 200-205 million years ago (Grimaldi and Engel 2005), or only more recently, nearly 160 million years ago (Rasnitsyn 1988, Whitfield 1993). The adaptations of the Hymenoptera to parasitism, which have made this group one of the best-adapted insects to host exploitation, involve the integration of three processes: (i) the use of limited nutritional resources by the immature stage, since the latter should finish its development in just one host; (ii) the allocation of part of these resources to the adult stage; and (iii) the acquisition and use of nutrients during the adult stage. The use of limited resources by the immature stage involves a series of morphofunctional adaptations and the development of diverse strategies for handling the host, which can involve the regulation of several of the host’s physiological processes aimed at optimizing nutrient acquisition and utilization (Vinson et al. 2001, Pennacchio and Strand 2006).
