Invasive moth pest spreads across western Japan causing tree mortality — Kyushu University conducts survey

In recent years, serious damage to agriculture, forestry, and urban greenery trees caused by invasive insects has been documented across Japan. The invasive lepidopteran pest Thecobathra lambda, first confirmed in Kyushu in 2017, is known to cause extensive damage to the leaves of American sweetgum (Liquidambar styraciflua), which is widely planted in streets and parks. However, its establishment status, invasion routes, and natural enemies had not been sufficiently investigated since its arrival.

A research team consisting of Assistant Professor Sadahisa Yagi from the Faculty of Agriculture at Kyushu University, Dr. Kota Sakagami from the Museum of Nature and Human Activities, Hyogo, Curator Shunsuke Tomura from the Tokushima Prefectural Museum, and Dr. So Shimizu from the National Agriculture and Food Research Organization conducted surveys of occurrence patterns and specimen investigations of Thecobathra lambda at 17 sites in western Japan. The results confirmed larval occurrence and feeding damage at 13 sites across Honshu, Shikoku, and Kyushu, with mass outbreaks also confirmed at four sites across four prefectures: Hyogo, Kagawa, Tokushima, and Ehime.

In Tokushima Prefecture, feeding damage to L. formosana, a tree species closely related to American sweetgum, was confirmed for the first time in Japan. Specimen surveys confirmed specimens collected in April and May at two sites in Fukuoka Prefecture, suggesting the possibility of overwintering. Additionally, genetic structure analysis based on the COI barcode region identified seven haplotypes, with unique haplotypes detected in several populations. The analysis results suggest that either multiple invasion events or a single large-scale invasion of a population with diverse genetic backgrounds occurring over a short period might have occurred.

Furthermore, five species of parasitoid wasps were confirmed as natural enemy insects of T. lambda. In particular, Diadegma armillatum, newly recorded in Japan, was found through parasitism rate surveys in Hyogo Prefecture to parasitize nearly half of the T. lambda larvae, demonstrating it to be the most promising natural enemy.

However, no correlation was observed between the larval density of T. lambda and the parasitism rate of natural enemy parasitoid wasps, with consistent parasitism confirmed even at low densities. Additionally, genetic structure analysis based on the COI barcode region of D. armillatum, the most promising natural enemy, revealed a common haplotype between Europe and Japan. The analysis results indicate anthropogenic distribution expansion over the long distance across the Eurasian continent that would not occur naturally.

This study revealed that T. lambda has expanded its distribution in western Japan beyond the initial confirmation of invasion. However, based on planting information for Liquidambar species, T. lambda has likely expanded its distribution over an even wider area, necessitating occurrence surveys across the entire archipelago. Although the potential use of D. armillatum as a biological control agent was suggested, it is a polyphagous natural enemy that also parasitizes species other than T. lambda. Careful evaluation is needed before using it as a biological control agent, including clarifying impacts on native ecosystems such as other moth species. Continued and wide-ranging research will be needed in the future regarding the elucidation of invasion origins and distribution expansion routes.

Yagi commented: "Thecobathra lambda is a small, white, cute-looking moth, but it is a serious pest that causes extensive damage, covering entire trees with white threads and, in the worst cases, causing tree mortality. In our surveys in western Japan, we discovered many interesting findings beyond our expectations, including the emergence of numerous parasitoid wasps and the confirmation of many haplotypes despite this being a recently confirmed invasive species. We anticipate that the distribution will continue to expand, and damage will be confirmed in wider areas in the future. Please take a look up at the Liquidambar trees near you."

Journal Information
Publication: Applied Entomology and Zoology
Title: Distribution range, genetic structure, and natural enemies of an invasive pest moth Thecobathra lambda (Lepidoptera: Yponomeutidae) damaging Liquidambar trees in Japan
DOI: 10.1007/s13355-025-00932-w