GENÉTICA DA ASSOCIAÇÃO DE INSETOS COM PLANTAS HOSPEDEIRAS

We present here the theoretical principles and main genetic methodologies for the study of speciation in insect herbivores. The presence of genetic polymorphism in herbivore populations may be associated to ecological factors, like the chemical variability in host plants. In this sense, we study the genetic-ecological relations like oviposition preference and larval performance, use of life tables of herbivore placed over different host plants, and mainly the geographic variation of characters associated to host plant exploitation. The use of the concept of host-race, or, herbivore populations that present specializations to a certain host plants, adds, to the study of crypyic species. We search the existence of these species when we find, in the same locus, different alleles fixed in different sympatric species host-races. We believe that host shifts were the prevalent events in the sympatric differentiation of herbivores, and that these would be associated to shifts in the polymorph characters associated to host exploitation. It is suggested that host shifts are associated to ecological and genetic restrictions. It is accepted that the great diversity of plant secondary chemicals evolved as a response to the attack of insect herbivores and that some insects evolved in response to the changes in their host plants, so, resulting from a diffuse coevolution between plants and herbivores. A similar process seeks to explain the patterns of herbivore and plant diversification, namely, “escape and radiation coevolution”. Finally, the analysis of phylogenies may provide evidence, based on the patterns of diversification of herbivores and their host plants, for the functions played by genetics, physiology, ecology, and geography in the evolution of these groups.