Host-use ability of a population of the herbivorous ladybird beetle Henosepilachna vigintioctomaculata depending on Solanum megacarpum in northern Honshu, Japan

Investigating the well-established relationships between insects and novel host plants will shed light on numerous aspects of evolution and ecology of phytophagous insects. However, in these systems, it is not always clear which plants were originally used as insect hosts, and how the focal insects adapted to the original host(s), before establishing the novel insect–host relationships. Henosepilachna vigintioctomaculata (Motschulsky) (Coleoptera: Coccinellidae) is a well-known pest of the potato Solanum tuberosum (Solanaceae), however its original host in Honshu, the main island of Japan, before the potato introduction is uncertain. A wild solanaceous weed, So. megacarpum, is the most likely candidate for the original host, although the use of this plant by H. vigintioctomaculata has never been recorded in Honshu. This study reports the occurrence of a H. vigintioctomaculata population depending almost solely on So. megacarpum at Yamagata, northern Honshu. Additionally, the host-use ability of this population was compared to that of a pest population under laboratory conditions. Based on the results obtained, it is discussed how the properties of beetles on So. megacarpum facilitated the use of the potato, assuming that So. megacarpum was the original host of H. vigintioctomaculata in Honshu.