Chemical and behavioral study on the phytomimetic giant geometer Biston robustum Butler (Lepidoptera: Geometridae)

Abstract

Polyphagous twig-like caterpillars of the giant geometer Biston robustum resemble the host plants not only in the morphological appearance, but also the surface chemicals as they change their cuticular chemicals after switching host plants. The object of this study is to investigate whether the caterpillars adjust the cuticular chemicals through direct body contact to the twigs or the ingestion of leaves after changing their host plants. The caterpillars successfully adjusted their cuticular chemicals to the new host plant when they fed on the plant's leaves, regardless of the plant species. The caterpillars' behavior was continuously under scrutiny, but direct body rubbing on the twigs was not observed. Thus, the caterpillars adjusted the cuticular chemicals through ingesting the leaves of the new host plant. Continuous behavioral observation revealed leaf clipping and body bending-and-stretching behaviors in the late instar caterpillars. Although the ethological meanings of the body bending-and-stretching behavior is uncertain, the leaf clipping, as well as morphological and chemical phytomimesis, would be adaptive as a countermeasure to predators.