Interactions between Large-Scale Inundative Releases of Trichogramma minutum (Hymenoptera: Trichogrammatidae) and Naturally Occurring Spruce Budworm (Lepidoptera: Tortricidae) Parasitoids

Abstract

A total of 480 million females of the egg parasitoid Trichogramma minutum Riley was aerially released on 30 ha of boreal forest infested by the spruce budworm, Choristoneura fumiferana (Clemens) in Ontario, Canada. T. minutum were released in parasitized eggs of the factitious host the Mediterranean flour moth, Ephestia kuehniella Zeller. Emergence of released T. minutum peaked at 80%, 5 d after the parasitoid releases. T. minutum were active attacking sentinal egg massess in the release plots up to 15 d after the 1st parasitoid release. The mean rate of parasitism of budworm egg masses by T. minutum was 68% in 3 treatment plots versus <2% in the matching control plots. The reduction in budworm density in the treatment plots from egg parasitism by T. minutum was maintained in the overwintering 2nd-instar budworms (October 1993) and for the 6th-instar budworms sampled in June 1994. Additional foliage protected in the treatment plots was between 37 and 51%. The rate of parasitism by the early-instar parasitoid Apanteles fumiferanae Viereck declined after the reduction of budworm populations in the treatment plots. In contrast, parasitism by the late larval tachinid complex, consisting primarily of Winthemia fumiferanae Tothill and Lypha setafacies (West), increased in the treatment plots. Aerial inundative releases with T. minutum can provide effective short-term population suppression of spruce budworm and significant foliage protection. The releases also complement the late larval parasitoids that have been suggested to be important in initiating a budworm population collapse.