Placenta-Like Structure of the Aphid Endoparasitic Wasp Aphidius ervi: A Strategy of Optimal Resources Acquisition

Abstract

Aphidius ervi (Hymenoptera: Braconidae) is an entomophagous parasitoid known to be an effective parasitoid of several aphid species of economic importance. A reduction of its production cost during mass rearing for inundative release is needed to improve its use in biological control of pests. In these contexts, a careful analysis of its entire development phases within its host is needed. This paper shows that this parasitoid has some characteristics in its embryological development rather complex and different from most other reported insects, which can be phylogenetically very close. First, its yolkless egg allows a high fecundity of the female but force them to hatch from the egg shell rapidly to the host hemocoel. An early cellularisation allowing a rapid differentiation of a serosa membrane seems to confirm this hypothesis. The serosa wraps the developing embryo until the first instar larva stage and invades the host tissues by microvilli projections and form a placenta like structure able to divert host resources and allowing nutrition and respiration of embryo. Such interspecific invasion, at the cellular level, recalls mammal's trophoblasts that anchors maternal uterine wall and underlines the high adaptation of A. ervi to develop in the host body.

The effect of different dietary sugars and honey on longevity and fecundity in two hyperparasitoid wasps

“…The chorion of hydropic eggs in most endoparasitoids is comprised of two separate layers, the serosa and the amnion, in which the developing wasp embryo is enclosed (Beckage and de Buron, 1994;Le Ralec, 1995). This 'porous' layer in the egg chorion enables nutrients in the host blood to be absorbed by the developing wasp embryo; the embryo is thus able to obtain the vast majority of essential nutrients from this solution for the completion of successful embryogenesis (Sabri et al, 2011). This adaptation is lacking in parasitoids that produce yolky, anhydropic eggs, such as G. agilis, where maternal protein investment is crucial.…”

Teratocytes and their functions in parasitoids

“…After being enveloped by the extraembryonic membrane, the embryo then ruptures out of the chorion and completes development inside the host [11 ,12 ,15,23,26]. Extraembryonic membranes play important roles in several aspects of endoparasitoid development including uptake of nutrients from the host, defense against the host immune system, and proliferation of embryos in taxa where polyembryony has evolved [23,26,[29][30][31]. Dissociation of the extraembryonic membrane after emergence of the wasp larva is also the source of the teratocytes produced by aphidiine braconids and members of the Scelioninae, Telenominae, and Teleasinae [11 ,12 ,15,17,29] (Figure 1b).…”

Aphid parasitoids in biological control

“…According to van Lenteren (2008), fewer than 20 species of natural enemies are presently reared on artificial media on a large scale. Rearing aphid parasitoids on a completely artificial medium is a further challenge, as they are koinobionts and thus have an intricate relationship with their host (Grenier and De Clerq 2003;Sabri et al 2011). Parasitoid eggs hatch after 24 h, producing first a morula and then a blastocoel structure consisting in a serosa enveloping the embryo (Bensadia et al 2006;Sabri et al 2011).…”

“…Rearing aphid parasitoids on a completely artificial medium is a further challenge, as they are koinobionts and thus have an intricate relationship with their host (Grenier and De Clerq 2003;Sabri et al 2011). Parasitoid eggs hatch after 24 h, producing first a morula and then a blastocoel structure consisting in a serosa enveloping the embryo (Bensadia et al 2006;Sabri et al 2011). This serosa behaves as a placenta-like structure, whose cells send microvillae inside the fat tissues of the host (Sabri et al 2011).…”

“…Parasitoid eggs hatch after 24 h, producing first a morula and then a blastocoel structure consisting in a serosa enveloping the embryo (Bensadia et al 2006;Sabri et al 2011). This serosa behaves as a placenta-like structure, whose cells send microvillae inside the fat tissues of the host (Sabri et al 2011). A second pseudo-hatching then occurs releasing the first instar larva in the host hemolymph.…”