Releases of parasitoids (Ceranisus spp.) as biological control agents of western flower thrips (Frankliniella occidentalis) in experimental glasshouses

Experimental releases were performed to investigate the potential of thrips parasitoids as biological control agents of western flower thrips, Frankliniella occidentalis (Pergande). Strains of two larval parasitoid species (Hymenoptera: Eulophidae), Ceranisus menes (Walker) (a strain from France and from Brazil) and Ceranisus americensis (Girault) (Arizona strain), were released in different commercial greenhouse crops. In all crops only traces of parasitism were recorded. In an experimental rose crop (cv. 'Frisco'), releases were made of two parasitoid species, C. menes (a French strain) and C. americensis (Arizona strain) in two separate greenhouse compartments. An account is given on the release, dispersal, establishment, population dynamics and control capacity of both parasitoid species. Parasitoids spread readily and established themselves throughout the crops, but releases did not result in reduction of thrips during a five month period. Rates of parasitism stayed lower than 10% throughout the season, resulting in severe damage of the rose crop. The potential of parasitoids as biological control agents of thrips pests in ornamental crops is discussed.