EVOLUTIONARY ROLE AND FATE OF THE INSECT PRIMARY OVIPOSITOR
The development of a piercing-sawing ovipositor for introducing eggs into the living plant tissues has made its owners independent of the soil characteristics and increased egg protection. This turned out to be the most important stimulus for the appearance of wings and flight, providing the winged insects with the tremendous opportunities for finding the new niches and unprecedented breadth of adaptive radiation. The ovipositor has passed through several stages of improvements and differentiation. The four principal types of the pterygote primary ovipositor are viewed: the Odonata, Diaphanopteroidea (only extinct forms), Cicadina (including Paraneoptera and Hymenoptera), and the Orthoptera types. A new hypothesis on the gonangulum homologies is put forward considering it a half of the IX sternite lateral of the midline plus the paratergite of the same segment. The constructions of the valvae and different homologies of the third valvae in the Polyneoptera and Eumetabola are discussed. The primary ovipositor has been repeatedly (i. e., in many lineages) reduced in the evolution of the Pterygota. The main circumstances of these reductions are: 1) subterranean (fossorial) habitation and life in narrow cavities of substrate; 2) aquatic life of the larvae, mostly linked with submerged oviposition; and 3) development and perfection of the flight to which heavy and protruding ovipositor is a hindrance. All holometabolous insects except Hymenoptera have no primary ovipositor.