Investigations on the influence of Diflubenzuron (Dimilin) on the host‐parasite‐system Spodoptera littoralis Boisd. (Lep., Noctuidae)/Microplitis rufiventris Kok. (Hym., Braconidae)
In the host‐parasite‐system Spodoptera littoralis/Microplitis rufiventris the oral administration of Dimilin (Diflubenzuron) affects differently the larval instars of the host and the endoparasite. The results obtained reveal that the non‐parasitized Spodoptera larvae (L4/1. day) were more susceptible to Dimilin than those which had been parasitized. Additionally there was no evidence in either group of a linear relation between dose and mortality. Mortality of the treated host larvae occurred both during after the process of moulting, but regardless of the dosage used, non‐parasitized and parasitized Spodoptera died rather after the moult L4/L5. The larva of Microplitis living endoparasitically in their host were injured by Dimilin, although moulting of the larva did not appear to be affected. After ingestion of a Dimilin dose which was lethal for the host a lengthening of the larval development occurred in Microplitis. While no significant change in the endophagous larval development was observed after a single application of Dimilin (at sublethal dosage), the treated Microplitis larvae required more time (2–3 days) for completion of their internal development after a double application (latent toxicity). Dimilin affected Microplitis by the following ways: larvae did not emerge from the host (0–14,1%) or incompletely emerged (0–43,4%), the larvae left the host but failed to build a complete cocoon (2,2–13,3%) or died during the cocoon stage (0–14,4%). These anomalies included encapsulation accompanied by melanization of the cuticle of the parasite and the death of the Microplitis larva.
The peritrophic membrane and the mid gut were severely damaged. The mortality of the parasites was related to the time of Dimilin application. A high susceptibility of the second stage of Microplitis was indicated by higher rates of mortality, when treatment occurred at this stage.
Zusammenfassung
In Untersuchungen zum Einfluß von Dimilin (Diflubenzuron) auf das Wirt‐Parasit‐System Spodoptera littoralis/Microplitis rufiventris wurde geklärt, welche Auswirkungen eine orale Aufnahme des Insektizids auf den Wirt selbst und auf die endoparasitisch lebenden Larven hat.
Nach einer Dimilin‐Behandlung im L4/1. Tag sind Mortalitätsunterschiede zwischen unparasierten und parasitierten Spodoptera‐Raupen festzustellen; parasitenfreie Raupen reagieren empfindlicher als parasitierte Raupen, mit Mortalitätsdifferenzen von 18‐35 %. Die Dosis‐Mortalitätsbeziehung ergibt keine lineare Abhängigkeit, sondern es treten in beiden Raupen‐Gruppen sog. Mortalitätssprünge und Mortalitätsplateaus auf. Ein Absterben behandelter Wirte findet nicht nur ‐ wie für Dimilin charakteristisch ‐ während, sondern auch nach der Häutung statt. Unabhängig von der Dosis und dem Parasitierungszustand tritt die Mortalität eher nach als während der Häutung ein.
Die Verabreichung einer ...
