Determining the host range of Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae), a candidate biological control agent for diamondback moth Plutella xylostella linnaeus (Lepidoptera: Plutellidae) in Canada

Abstract

Before a non-native agent is introduced for the classical biological control of a pest, its host specificity must be determined. We assessed the host specificity of Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae), a solitary pupal endoparasitoid being considered for biological control of the diamondback moth Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) in Canada. In black-box no-choice tests on nine non-target species, D. collaris successfully parasitized other species in the genus Plutella (the introduced Plutella porrectella Linnaeus and the native Plutella armoraciae Busck) as well as another introduced agricultural pest, the leek moth Acrolepiopsis assectella (Zeller) (Lepidoptera: Glyphipterigidae). This suggests that the fundamental host range of D. collaris includes other species in the Plutellidae, as well as Glyphipterigidae that are ecologically and morphologically similar to diamondback moth. Field tests in Switzerland comparing parasitism by D. collaris on sentinel diamondback moth pupae and leek moth pupae in both canola and leek fields revealed no parasitism of leek moth in leek fields, indicating that the ecological host range of D. collaris is in fact more restricted. Because of this, it would be premature to discount D. collaris as a potential biological control agent for diamondback moth in Canada.