ORIGINAL ARTICLE Host range expansion by Rhopalomyia yomogicola (Diptera: Cecidomyiidae) from a native to an alien species of Artemisia (Asteraceae) in Japan Machiko NOHARA 1 , Tomoko GANAHA 1 , Nami UECHI 3 , Shinsuke SATO 2 and Junichi YUKAWA 2 1 Entomological Laboratory, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 2 Kyushu University, Fukuoka, and 3 Okinawa Prefectural Agricultural Research Center, Itoman, Japan Abstract In 2001, subconical galls were found on the leaves of an alien Artemisia species (Asteraceae) in Ibusuki City, Kagoshima Prefecture, Japan. These galls were quite similar to those induced by Rhopalomyia yomogicola (Diptera: Cecidomyiidae) on Artemisia princeps, Artemisia montana, and Artemisia japonica in Japan. The morphological features of the pupal head and molecular sequencing data indicated that the gall midge from the alien Artemisia was identical to R. yomogicola. Usually, galling insects do not expand readily their host range to alien plants, but R. yomogicola is considered to have expanded its host range to the alien Artemisia by its multivoltine life history trait and oligophagous habit across two different botanical sections of the genus Artemisia. Adult abdominal tergites and sternites and immature stages of R. yomogicola are described for the first time and detailed biological information is presented. Key words: gall midge, leaf gall, mtDNA COI region, multivoltine, oligophagy, pupal frontal area. INTRODUCTION Several hundred species of alien plants (Angiospermae), called “recent arrivals” (Maekawa 1973), have natural- ized in Japan since the 1850s when the Japanese gov- ernment opened the country to foreign trade after a long-term isolation of about 250 years (Washitani & Morimoto 1993). Since the 1950s, various alien plants, including some congeneric with Japanese species, have been brought into Japan to spray their seeds on slopes to prevent landslip after road construction (Sasaki 2002). These plants include species of Lespedeza (Fabaceae), Sicyos (Cucurbitaceae), Artemisia, Chrysanthemum, Ambrosia (Asteraceae), and other genera of Poaceae. The spreading of alien plants has been causing serious problems in Japan in recent years (e.g. Murakami & Washitani 2002). Yukawa and Uechi (1999) pointed out that galling insects seldom expand their host range to alien plants because of the difficulty in establishing themselves on newly encountered plants due to difficulties in gall induction, a delicate event during the course of cell division, tissue differentiation, shoot extension, and other processes of plant growth. For example, Japanese gallers utilize only 0.7% of 607 alien Angiospermae species as hosts, which is distinctly lower than the 13.1% of 4162 domestic Angiospermae used (Yukawa & Uechi 1999). Nevertheless, in October 2001 we found several subconical midge galls on leaves of an alien Artemisia species on the roadside of a newly con- structed area in Ibusuki City, Kagoshima Prefecture, Japan. These galls were quite similar to those induced by a domestic gall midge, Rhopalomyia yomogicola (Mat- sumura) (Diptera: Cecidomyiidae), on native Artemisia princeps Pampanini, Artemisia montana (Nakai) Pam- panini, and Artemisia japonica Thunberg to Japan Correspondence: Junichi Yukawa, Kyushu University, Hakozaki 6-10-1, Higashi–ku, Fukuoka, 812-8581 Japan. Email: JZS02305@nifty.ne.jp Received 25 March 2007; accepted 7 May 2007. Entomological Science (2007) 10, 353–361 doi:10.1111/j.1479-8298.2007.00239.x © 2007 The Entomological Society of Japan