Population establishment of the leafroller Eudemis gyrotis (Lepidoptera: Tortricidae) at a new plantation of bayberry Myrica rubra (Myricaceae)

Abstract

To clarify the immigration process of a phytophagous insect to a new habitat, I examined seasonal changes in the abundance and parasitism of larvae and pupae of a leafroller, Eudemis gyrotis (Meyrick) (Lepidoptera: Tortricidae), at both a new and an old plantation of the bayberry Myrica rubra Sieb. et Zucc. (Myricaceae) on Mt. Tanakami, Shiga Prefecture, central Japan, in 1999. E. gyrotis adults singly lay eggs on only young leaves of M. rubra, and their larvae feed on the leaves. Therefore, the young leaves of M. rubra are necessary for the occurrence of E. gyrotis larvae. The number of E. gyrotis larvae per tree was correlated with the amount of young leaves per tree. At the old plantation where E. gyrotis had already been found in 1998, the larval occurrence of E. gyrotis began in late May. At the new plantation, which was at a distance of ca. 600 m from the old plantation, E. gyrotis larvae had not occurred by late July, although there was an abundance of young leaves of M. rubra in late May. These findings suggest that E. gyrotis adults that had emerged from the old plantation in July immigrated to the new plantation and laid eggs on the plants there. The parasitoids that attacked E. gyrotis at the new plantation just after immigration were polyphagous. This suggests that those parasitoids switched hosts from other herbivore species to E. gyrotis. In spite of the attack by polyphagous parasitoids, the E. gyrotis population successfully established itself at the new plantation.