1Bio-oriented Technology Research Advancement Institution, Tokyo 105- 0001, Japan.
2Laboratory of Ecological Information, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
We investigated the inter-habitat migration by Oligota kashmirica benefica, an insect predator of spider mites, from weed communities infested by Tetranychus spider mites to a mulberry community infested by Eotetranychus spider mites. When we started field investigations, several hundred Oligota beetles were found in the weed communities, whereas no beetles were in both the mulberry community and other places within a radius of ca. 20 m from the latter community. In the mulberry community, a total of 412 Oligota beetles was captured during ca. 2-month investigation period, especially after the destruction of the weed communities by mowing. The results of mark-release-recapture experiment and of flight-behavior observation of the predators demonstrated their long-range inter-habitat migration (ca. 5-20 m) from the weed communities to the mulberry community by flight during the daytime. The results of the flight-behavior observation and of olfactometer bioassays in a laboratory indicated the involvement of the volatile cues from mulberry plants infested by Eotetranychus mites in the long-range flight migration. No fertilized females of the predators collected from the mulberry community started ovipositing when offered Eotetranychus mites on the mulberry leaves in a laboratory for 5 days, whereas 91.7% of them oviposited during the same period when offered Tetranychus mites on the weeds. These results indicated that the inter-habitat flight migration by O. kashmirica benefica to the mulberry comminity, less suitable habitat, was caused by the destruction of the suitable habitat, i.e. the weed communities.