Abstract

We observed the seasonal occurrence of diamondback moth (DBM) larvae, Plutella xylostella (Lepidoptera: Plutellidae), and their native parasitoid wasps, Cotesia vestalis (Hymenoptera: Braconidae), on mizuna plants, Brassica rapa var. laciniifolia (Brassicales: Brassicaceae), in three commercial greenhouses and on wild cruciferous weeds, Rorippa indica (Brassicales: Brassicaceae), in the surrounding area in the Miyama countryside in Kyoto, Japan. The occurrences of DBM larvae in greenhouses followed their occurrence in the surrounding area: however, some occurrences of DBM in greenhouses took place when the DBM population in the surrounding was rather low. This suggests that the occurrence of DBM in greenhouses cannot always be explained by its seasonal occurrence in the surrounding areas. The occurrence of C. vestalis followed that of DBM larvae in mizuna greenhouses and in the surrounding areas. No C. vestalis were recorded in greenhouses when DBM was not present. Cotesia vestalis females preferred volatiles emitted from DBM-infested mizuna plants to those from uninfested conspecifics under laboratory conditions. Natural HIPVs (herbivory-induced plant volatiles) emitted from DBM-infested mizuna plants in greenhouses probably attracted C. vestalis from the surrounding area to cause their co-occurrence.