Open Access

Gernot Hoch, Sabrina Verucchi, Axel Schopf

• Since the late 1990s, the oak processionary moth, Thaumetopoea processionea (L.), has been occurring at high population densities in eastern Austria. Particularly, infestations in areas of human settlement have created increasing interest in this insect due to health problems caused by the urticating hairs of the larvae. New methods for biological control are desirable. Like essentially all forest Lepidoptera, T. processionea is host for entomopathogenic microsporidia. These obligatory parasitic protists have been evaluated as biocontrol agents against an other oak pest, Lymantria dispar (Weiser & Novotny, 1987; Jeffords & al., 1988). Life history traits of T. processionea make this insect an even more promising target for the use of microsporidia. The larvae are highly gregarious and stay together in nests made of larval silk for resting periods and molting. Microsporidia utilize several pathways for horizontal transmission that would be aided by these features: spores can be released after host death from cadavers as well as from living larvae via silk or feces. Additionally, many microsporidia are vertically transmitted (summarized in Maddox & al., 1998). In this project, T. processionea larvae from various regions in eastern Austria were screened for the natural occurrence of microsporidia. One isolate, Endoreticulatus sp., was further studied and mass produced in a laboratory host, L. dispar, that is easy to rear and does not pose a health hazard for people working with the insects. An inoculative release was attempted on isolated trees infested with T. processionea.
• In einem zweijährigen Screening untersuchten wir das Auftreten von Mikrosporidien bei Thaumetopoea processionea an verschiedenen Standorten in Ostösterreich. In neun von 18 Populationen wurden Mikrosporidiosen nachgewiesen, die Prävalenzen lagen zwischen 1,9 % und 15,4 %. Basierend auf lichtmikroskopischen Befunden waren die gefundenen Pathogene den Gattungen Endoreticulatus, Nosema, Cystosporogenes und Vairimorpha zuzuordnen. Endoreticulatus sp. vermochte im Labor Raupen von Lymantria dispar zu infizieren. Das erlaubte die einfache Produktion von Inokulum sowie Untersuchungen mit einem ungefährlichen Wirtsinsekt. Laborversuche mit L. dispar zeigten einen langsamen Krankheitsverlauf, der aber in signifikant erhöhter Mortalität resultierte (nur 26 % der oral inokulierten Tiere entwickelten sich zu Imagines), sowie eine effiziente horizontale Übertragung. Eine inokulative Freilassung wurde versucht: dazu wurden Endoreticulatus-Sporen in wässriger Suspension auf Blätter isoliert stehender, von T. processionea befallenen Eichen ausgebracht. Die Inokulation war erfolgreich, allerdings auf niedrigem Niveau – die maximale Infektionsrate lag bei 9,5 %.