Notes on incidence and biology of the predominant parasitoids attacking the cottonwood leaf beetle in Minnesota

Abstract

Populations of the cottonwood leaf beetle, Chrysomela scripta Fabricius (Coleoptera: Chrysomelidae), in Minnesota were examined for the presence of parasitoids over a period of two years. Field samples of larvae and pre-pupae yielded two parasitoids: a tachinid fly, Cleonice setosa (Reinhard), and a pteromalid wasp, Schizonotus sieboldi (Ratzeburg). Incidence of parasitism by the tachinid was substantially higher than in previous reports, with 32.9% of third instar larvae and 81.4% of pre-pupae being parasitized. The pteromalid was present in 7.0% of pre-pupae. Both parasitoids were reared to adulthood in the laboratory, with the pteromalid exhibiting continued generations, but the tachinid completing development only after a cold treatment to break diapause.