Occurrence of diamondback moths Plutella xylostella and their parasitoid wasps Cotesia vestalis in mizuna greenhouses and their surrounding areas

Pest insects invade commercial greenhouses from the surrounding areas. We aimed to clarify whether (1) the seasonal population dynamics of local pest insects affects their greenhouse invasions and (2) carnivorous natural enemies of the pests mirror this invasion. We compared the occurrence of diamondback moth [DBM: Plutella xylostella (Lepidoptera: Plutellidae)] larvae and their native parasitoid wasps Cotesia vestalis (Hymenoptera: Braconidae) on mizuna plants [Brassica rapa var. laciniifolia (Brassicales: Brassicaceae)] in commercial greenhouses, with their population dynamics on a wild cruciferous weed Rorippa indica (Brassicales: Brassicaceae) in satoyama in Kyoto, Japan. C. vestalis followed the occurrence of DBM larvae on both mizuna and R. indica; no C. vestalis were recorded in greenhouses free from DBM larvae. C. vestalis females were more attracted to volatiles emitted from DBM-infested than from uninfested mizuna. However, the presence of DBM in greenhouses could not always be explained by its seasonal population dynamics in the surroundings.