Pre-emptive augmentative biological control of Spodoptera frugiperda in Europe using Trichogramma spp.

Abstract Background Fall armyworm, Spodoptera frugiperda , is a highly invasive pest of maize and other crops worldwide. It has recently been detected in Europe, and it is urgent to test and develop new sustainable control methods adapted to the European context and market. Trichogramma spp. are egg parasitoids that are sometimes used as biological control agent against S. frugiperda in other continents. However, a major issue using Trichogramma spp. against this pest is that females cannot reach all eggs in an egg mass, which is usually composed of one to three layers of eggs, often covered with scales and hair. Three European Trichogramma species were tested for their ability to parasitize egg masses with one to three layers and with or without hair and scale cover. Methods Trichogramma brassicae , T. dendrolimi and T. cacoeciae were offered five types of S. frugiperda egg masses: one-layer without hair; one-layer with hair; two-layers without hair; two-layers with hair; three-layers with hair. For each treatment, an egg mass laid on paper was placed in a small vial saturated with females, to be sure that all reachable eggs would be parasitized. For each egg mass, the number of eggs in each layer was counted. Fifteen replicates were made per treatment, as well as 10 control vials without Trichogramma sp. Parasitism rates were calculated for each egg mass. Results There were significant differences in the ability of parasitoid species to oviposit through hair and scales and to reach the lower egg layers. Trichogramma dendrolimi was the most efficient species and T. cacoeciae the least. Depending on the number of egg layers and hair and scales, parasitism rates by T. brassicae , T. dendrolimi and T. cacoeciae varied between 99 and 41%, 100 and 43% and 100 and 28%, respectively. Conclusions The assays confirmed that Trichogramma females cannot easily oviposit through thick layers of hair and scales but overall parasitism rates were higher than found previously. Important variations between species were found, and more Trichogramma sp. and other local natural enemies should be tested pre-emptively before S. frugiperda has invaded Europe.