The parasitoid fly Exorista japonica uses visual and olfactory cues to locate herbivore-infested plants

Some parasitoid flies exploit odors derived from plants as olfactory cues for locating the food plants of host insects, but the role of visual cues associated with plants remains largely unknown. The generalist tachinid Exorista japonica Townsend (Diptera: Tachinidae) is attracted to odors derived from maize plants [Zea mays L. (Poaceae)] infested by the larvae of Mythimna separata (Walker) (Lepidoptera: Noctuidae). In this study, we examined the effects of visual parameters on the olfactory attraction of female flies to host-infested plants. A paper plant model of one of four colors (blue, green, yellow, or red) was placed in front of a host-infested plant, which was hidden behind a mesh screen in a wind tunnel. The landing rate of females was significantly higher on the green plant model than on the other three models. When an achromatic plant model of one of four gray scales (white, light gray, dark gray, or black) was tested, the response rate of females was significantly higher towards the white model and decreased as the brightness of models decreased. Few female flies responded to the green plant model without odors of the host-infested plants. When the four color plant models were placed together in a cage filled with odors of host-infested plants, females remained significantly longer on the green model than on the other three models. These results showed that E. japonica females preferred the color green when odors of the host-infested plants were present and suggest that E. japonica uses visual as well as olfactory cues to locate the host habitat.