Female butterflies that eat alien plants may become less attractive to males

A research group including Graduate Student Karen Hisai, Associate Professor Shouhei Ueda, Research Fellow Tsuyoshi Takeuchi, Research Fellow Masahiro Suzuki, and Professor Norio Hirai of the Graduate School of Agriculture at Osaka Metropolitan University, along with Lecturer Masaya Yago of the University Museum at the University of Tokyo, has shown that when females of the near-threatened butterfly Tongeia fischeri grow up eating an alien plant during their larval stage, the reflection spectrum of their wings as adults changes, and wild males become less likely to choose them as mates. The findings provide evidence that alien plants may not directly harm butterfly survival but can indirectly hurt reproduction by changing visual signals. The results were published online in Basic and Applied Ecology.

In recent years, there has been global concern about the impact of alien plant species invasion on native ecosystems. The near-threatened butterfly T. fischeri in Japan mainly uses the native plant Orostachys japonica as its host plant, but in recent years it has been observed using alien plants such as Sedum sarmentosum.

It had been suggested that the wing color of adult butterflies changes depending on the type of host plant eaten during the larval stage, but no experimental study had confirmed this. It is also known that wing color plays an important role as a visual signal in butterfly mating behavior. The research group thought that alien plants eaten during the larval stage might affect wing color in adults, and in turn affect mating behavior.

First, larvae of T. fischeri were raised on either the native plant O. japonica or the alien plant S. sarmentosum, and their life history traits were compared. The results showed that female adults laid eggs on both native and alien plants and showed no clear preference for either. No significant differences were found between the two plants in traits such as larval development period or pupal weight, showing that the butterflies can develop normally on the alien plant as well.

Next, visible light and ultraviolet photographs of the adult wing undersides were taken and reflectance spectra were measured for comparison and validation. In visible-light photographs, individuals raised on the native plant looked yellowish, while those raised on the alien plant looked grayish. In ultraviolet photographs, individuals raised on the native plant absorbed more ultraviolet light, appearing as a darker gray. The reflection spectrum measurements showed the same trends.

When wild male T. fischeri were observed to see which females they preferred, males made significantly more contact with and showed stronger mating behavior toward individuals raised on the native plant than those raised on the alien plant. This trend was also confirmed in experiments with specimens that were less affected by odors (pheromones).

This study is a very valuable case in Japan showing that alien plants can indirectly affect reproduction through a morphological mutation, i.e., wing color change, in adult butterflies.

The number of alien species is increasing year by year, and similar cases may occur in butterfly and insect species other than T. fischeri in the future. The findings obtained in this study will serve as a model case to highlight the indirect threats posed by alien plants to plant-eating insects and are expected to contribute to the conservation of other endangered insect species and to solving the problem of alien species.

Hisai commented: "We found that butterflies raised on alien plants, despite developing normally, become less likely to be chosen as mates by wild males. It was very interesting to discover that a near-threatened butterfly may be losing mating opportunities in the ultraviolet world, a world invisible to human eyes. I hope this research can offer a new perspective not only for butterfly conservation, but also for future insect conservation efforts more broadly."

Journal Information
Publication: Basic and Applied Ecology
Title: Effects of alien host plant on wing coloration and mating behavior of an endangered butterfly
DOI: 10.1016/j.baae.2026.02.003