Development of the Parasitoid Microplitis rufiventris Reared in Hosts Treated with Lefenuron, a Chitin Synthesis Inhibitor

Abstract

Eggs and larvae of Microplitis rufiventris Kok. (Braconidae: Hymenoptera) were exposed to two sublethal concentrations (0.2 and 0.4 ppm) of the chitin synthesis inhibitor lefenuron, by feeding treated artificial diet to their hosts, Spodoptera Uttoralis (Boisd.) (Noctuidae: Lepidoptera) larvae. Each concentration was initiated during the egg stage or different instars of the parasitoid larvae. Between 4.3 and 33.8% of parasitoid larvae in lefenuron-treated hosts showed morphological and developmental abnormalities. The effect of the compound on the developmental rate and sensitivity of the parasitoid larvae varied according to the parasitoids' age at treatment; the egg stage and older parasitoid larvae were more tolerant to the compound than the first instars. In all treated hosts the developmental rate of the parasitoid was lower than that of controls. The lower lefenuron concentration (0.2 ppm) was more effective at disrupting the development of young parasitoid larvae than the higher one. Delayed or latent effects of the compound were evident in non-emergence of parasitoid adults that were exposed to the compound as first instars. Reduced sensitivity of old parasitoid larvae could be compatible with survival of the parasitoid in integrated control programme of S. Uttoralis. Resume-Les oeufs et larves de Microplitis rufiventrisKok. (Hymenoptera: Braconidae) etaient exposes a deux concentrations sub-letales (0,2 et 0,4 ppm) de lefenuron, un inhibiteur de synthese de la chitin, par alimentation sur milieu artificiel des chenilles de Spodoptera Uttoralis (Boisd.) (Lepidoptera: Noctuidae) qui sont des notes du braconide. Chaque dose etait administree au stade oeuf ou a des differents stades larvaires du parasitoide. Les chenilles nourries au lefenuron ont revele entre 4,3 et 33,8% de larves mal developpees du parasitoi'de et possedant des anomalies morphologiques. L'effet du lefenuron sur le taux de croissance et de developpement ainsi que sur la sensibilite des larves variaient avec l'age du parasitoide, au moment du traitement. Les oeufs et larves agees du parasitoide etaient plus tolerants vis-a-vis du produit plus que les jeunes stades. La basses concentration du lefenuron pertubait le developpement des jeunes larves plus que les concentrations elevees. L'arriere-effet et la latence du produit etaient manifestes et ils etaient refletes par la non-emergence des adultes chez les larves exposees au produit a leur premier stade de developpement. Dans un programme de lutte integree contre S. Uttoralis, une sensibilite reduite des larves agees du parasitoide pourrait presager une survie du parasitoide.