Parasitoid Venom Research Articles

Polydnavirus and venom of the egg-larval parasitoid Chelonus inanitus (Braconidae) induce developmental arrest in the prepupa of its host Spodoptera littoralis (Noctuidae)

The egg-larval parasitoid Chelonus inanitus induces in its host Spodoptera littoralis precocious onset of metamorphosis in the penultimate stadium and developmental arrest in the precocious prepupa. At oviposition the wasp injects, along with the parasitoid egg, venom and calyx fluid that contains polydnaviruses. By using indirect and direct approaches we have investigated the role of polydnaviruses and venom in influencing host development. When parasitoid development was prevented by either X-ray irradiation of wasp females or heat-treatment of parasitized eggs, hosts developed normally up to the prepupal stage but then became developmentally arrested. Injection of calyx fluid and venom into eggs also led to developmental arrest in the prepupa, while injection of anti-polydnavirus antibodies into eggs before parasitization prevented successful parasitoid development and rescued hosts so that they pupated normally. These results show that polydnavirus and venom induce developmental arrest in the prepupa but do not induce precocious onset of metamorphosis. Venom alone was ineffective in causing developmental arrest, and calyx fluid alone was effective only at high doses; but together with 0.0048 wasp equivalents of venom, as little as 0.0005 wasp equivalents of calyx fluid per egg was sufficient to induce developmental arrest. SDS-gel electrophoretic analyses of purified polydnavirus and venom showed that both consist of a great number of polypeptides of various sizes, and Western blots revealed that the anti-polydnavirus antibodies crossreacted with several venom proteins.

Effect of the venom of the gregarious parasitoid Apanteles glomeratus on its hemocytic encapsulation by the host, Pieris

When eggs from the lateral oviduct of the gregarious parasitoid Apanteles glomeratus were injected with calyx fluid and venom apparatus material into host larvae, Pieris rapae crucivora, most of the eggs were not encapsulated. Apanteles eggs deposited by the parasitoid from which the venom apparatus was removed were usually encapsulated by the host. These results indicate that the parasitoid venom apparatus material is an important factor in suppressing the encapsulation of 1- or 2-day-old eggs in the host. In order to clearly demonstrate that the venom suppresses egg encapsulation but not the encapsulation of other foreign objects, DEAE-Sephadex A-50 ion-exchange particles stained with 0.001% (w/v) Congo Red solution were injected into hosts together with venom apparatus material. The Sephadex particles were encapsulated by host hemocytes. The results suggest that the venom does not inhibit the encapsulation ability of the host.