Non-target host acceptance and parasitism by Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) in the laboratory

Abstract

Abstract As part of a risk assessment study, we exposed eggs of 23 non-target lepidopteran species including nine butterflies endangered in Switzerland to individual Trichogramma brassicae Bezdenko females under no-choice conditions in the laboratory. We could show that Papilio machaon L. (Papilionidae), Artogeia (= Pieris ) napi L. (Pieridae), Argynnis adippe Denis & Schiffermuller, Clossiana titania Esper, (Nymphalidae), Aphantopus hyperanthus L., Maniola jurtina L., Coenonympha pamphilus L., Melanargia galathea L., Erebia ligea L., Hipparchia alcyone Denis & Schiffermuller (Satyridae), Polyommatus icarus Rottemburg and Plebejus idas L. (Lycaenidae) were well accepted and not parasitized significantly different (range 73–94%) than the target, Ostinia nubilalis Hubner (81%). Virtually all eggs of Vanessa atalanta L., Argynnis niobe L., Clossiana selene L. (Nymphalidae), and Cyaniris semiargus Rottemburg (Lycaenidae) were accepted for oviposition resulting in significantly higher parasitism rates of 94–97% compared with the target. Melitaea parthenoides Keferstein, M. diamina Lang, and nearly 50% of Mellicta athalia Rottemburg (Nymphalidae) eggs were rejected early in the host selection process. Ovipositional success on eggs of Zygaena filipendula L. (Zygaenidae), Hesperia comma L. (Hesperidae), Sphinx ligustri L., and Deilephila elpenor L. (Sphingidae) was less than 30%. The number of times a female left a host egg before acceptance as well as the time from first host egg contact to acceptance was not related to parasitism rate on the tested non-targets. Offspring emerging from non-target hosts was of similar or even larger size compared to offspring emerging from the target, and in all cases larger compared to individuals emerging from the factitious host, Ephestia kuehniella Zeller. We found that large T. brassicae individuals had significantly higher success in penetrating the chorion and parasitizing eggs of S. ligustri than smaller adults. The results show that T. brassicae parasitizes a number of non-target lepidopteran eggs belonging to different families. Host range and impact under field conditions have yet to be determined.