Herbivory by Strongylocoris leucocephalus (Hemiptera: Miridae) on a novel host plant Adenophora triphylla var. japonica in Japan

When monophagous and oligophagous insect herbivores colonize new areas, they sometimes use novel hosts. The availability of the new hosts can facilitate further expansion into regions beyond the geographic range of the original hosts, resulting in specialization on different host plant taxa in different parts of the herbivore's geographic range. Strongylocoris leucocephalus Linnaeus (Hemiptera: Miridae), which is a plant bug attacking Campanula spp., is widely distributed in the Eurasian continent, North Africa, and northern Japan. In the process of geographic range expansion, S. leucocephalus may incorporate novel host plants into their host range. I investigated the host plant species of S. leucocephalus in central Japan. Field observations revealed that the plant bug fed on the novel host plant Adenophora triphylla (Thunb.) A. DC. var. japonica (Regel) H. Hara (Campanulaceae), although feeding by S. leucocephalus was not associated with plant mortality. However, S. leucocephalus never fed on Campanula punctata Lam. var. hondoensis (Kitam.) Ohwi, the only Campanula species at the study site. The plant bug S. leucocephalus and the novel host plant A. triphylla var. japonica are not entirely distributed sympatrically, suggesting that the plant bug has expanded its geographic range by incorporating new hosts.