Polyembryonic Insects by Kikuo Iwabuchi

Author:Kikuo Iwabuchi
Language: eng
Format: epub
ISBN: 9789811509582
Publisher: Springer Singapore

3.1.4 Host Entry by Tissue-Compatible Invasion in the Polyembryonic Encyrtid Copidosoma floridanum

3.1.4.1 Host Invasion by Motile Morulae

Copidosoma floridanum is an egg–larval parasitoid. During egg parasitization , the parasitoid eggs that are laid inside the host eggs can almost evade host immunity because insect eggs, particularly newly laid eggs, lack a functional immune system (Salt 1968). In the case of idiobiont egg parasitoids, embryogenesis of the host ceases shortly after parasitization, following which the host embryo is lysed and consumed by the parasitoid embryos that exist inside or outside the host embryo. However, for koinobiont endoparasitoids that lay their eggs inside the host egg and complete their development in later host stages, host entry is essential for the completion of development. These parasitoids enter the host body by laying eggs directly inside the mature embryo or in the yolk of the host egg, following which the newly hatched larvae bore into the host embryo (Quicke 1997). Species in the genus Chelonus (Braconidae) use several strategies to enter the host body depending on the stage of the host embryo at the time of parasitism, including passive infiltration through the dorsal opening, larval boring into the host body, and oviposition directly into the mature host embryo (Rosenberg 1934; Wishart and van Steenburgh 1934; Clausen 1972; Hawlitzky 1972, 1979; Rechav and Orion 1975; Kaeslin et al. 2005). Entry into the host embryo by the newly hatched larva is also known in Ascogaster spp. (Clausen 1972). Thus, in many egg–larval parasitoids, the action of the motile larvae as well as direct oviposition into the host egg is important for entering the host embryo. However, this is not the case in C. floridanum, which has a prolonged embryonic stage.

In vitro studies have shown that the morula -stage embryo of C. floridanum is motile (Fig. 3.2) and enters the host embryo by changing its shape. In this case, the morula actively invades the host embryo without damaging the host cells (Fig. 3.3). This ability allows C. floridanum to lay its eggs in the yolk (i.e., outside the embryo) of early-stage host eggs and subsequently enter the host embryo after development to the morula stage (Nakaguchi et al. 2006). Such parasitization by moving embryos is a novel parasitization method among insect parasitoids. The ability of the morula to invade the host embryo decreases with host embryonic development. Thus, in older host eggs, parasitoid entry into the host embryos is accomplished by direct oviposition into the host embryo, though in some instances the morula-stage embryo can also enter the later-stage host embryo through the navel opening on the dorsal thorax of the host (Nakaguchi et al. 2006).

Fig. 3.2Movement of a C. floridanum morula (26 h after oviposition) in vitro. (a) Track of a morula migration on the surface of a culture well during 7 h, (b–d) movement of a morula. (Nakaguchi et al. 2006)

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.