Selecting the right parasitoid for the environment in classical biological control programmes: the case of Diadegma semiclausum (Hymenoptera: Ichneumonidae) and Plutella xylostella (Lepidoptera: Plutellidae) in the Kofele highland of Ethiopia

The careful selection of parasitoids with a track record of success in similar environmental conditions may increase the likelihood of effective biocontrol. Diamondback moth (DBM) population and level of parasitism were assessed for three years prior to the release of Diadegma semiclausum (Hellen) in June 2008. Thereafter, the DBM population and severity of crop damage and the occurrence of D. semiclausum and indigenous DBM parasitoids were monitored by monthly surveys during the main production season of June to December for three years. Before release, DBM numbers fluctuated between 4.2 and 11.2 per plant and parasitism ranged between 6.5 and 24.7%. DBM density declined to 2.8, 0.9 and 0.7 per plant whilst parasitism levels increased successively to 21, 39 and 38% in 2008, 2009 and 2010, respectively. A significant shift in parasitoid guild was observed after D. semiclausum release: it comprised 18.6, 80.3 and 88.6% of total parasitism in the first, second and third year, respectively. The decline of DBM density following the release of the introduced parasitoid and its establishment will ensure production of Brassica spp. without pesticide use against DBM in the affected area.