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 Spodop tera littoralis precocious onset of metamorphosis in the penultimate s tadium and developmental arrest in the precocious prepupa, At oviposit ion the wasp injects, along with the parasitoid egg, venom and calyx f luid that contains polydnaviruses. By using indirect and direct approa ches we have investigated the role of polydnaviruses and venom in infl uencing host development, When parasitoid development was prevented by either X-ray irradiation of wasp females or heat-treatment of parasit ized eggs, hosts developed normally up to the prepupal stage but then became developmentally arrested, Injection of calyx fluid and venom in to eggs also led to developmental arrest in the prepupa, while injecti on of anti-polydnavirus antibodies into eggs before parasitization pre vented successful parasitoid development and rescued hosts so that the y pupated normally, These results show that polydnavirus and venom ind uce developmental arrest in the prepupa but do not induce precocious o nset of metamorphosis, Venom alone was ineffective in causing developm ental arrest, and calyx fluid alone was effective only at high doses; but together with 0.0048 wasp equivalents of venom, as little as 0.000 5 wasp equivalents of calyx fluid per egg was sufficient to induce dev elopmental arrest, SDS-gel electrophoretic analyses of purified polydn avirus and venom showed that both consist of a great number of polypep tides of various sizes, and Western blots revealed that the anti-polyd navirus antibodies crossreacted with several venom proteins. Copyright (C) 1996 Elsevier Science Ltd