Host frass as arrestant chemicals in locating host Mythimna separata by the tachinid fly Exorista japonica

We investigated the response of the tachinid fly, Exorista japonica (Townse nd), to host frass or its extracts in order to clarify the host location me chanisms of female flies in a potential host habitat. Host searching time i n a patch and the number of patch visits were analyzed by using a frass-con taining patch which was excreted by host larvae, Mythimna separata (Walker) (Lepidoptera: Noctuidae), and patches to which host frass extracts were ap plied. E. japonica females were arrested in response to the host-frass-cont aining patch after contacting the frass with their front tarsi, thereby spe nding most of the time to search the patch and to revisit the host-frass pa tch. While host-searching time in the patch by the females was longest at t heir first visit of a patch with host frass, searching time decreased with successive visits. The female flies also exhibited area-restricted searchin g with methanol extracts of the host frass. Area-restricted searching activ ity increased with the concentration of host-frass extract, i.e., total sea rching time in the patch and the number of patch visits varied in a dose-de pendent manner. E. japonica females likely employ chemicals in host frass a s arrestants in host location.