Laboratory of Biology, Okaya, Nagano, Japan

Iguchi Lab - Research

Iguchi explores forests for beetles.

Yutaka Iguchi, Director, Laboratory of Biology

Yutaka Iguchi
Director, Laboratory of Biology

My major research focuses on the ecology, behavior and morphology of coleopteran species. I have been particularly engaged in field and laboratory studies on “Kabutomushi” (Japanese horned beetle, Trypoxylus dichotomus), “Kuwagatamushi” (stag beetles such as Dorcus rectus and D. binervis ) and “hotaru” (fireflies) in Nagano and its surrounding prefectures.

These coleopteran species are very familiar to Japanese people, but their interesting morphological and behavioral characteristics such as horn or mandible polymorphism and alternative tactics have not yet been fully explored.

For example, it is well-known that male T. dichotomus exhibits horn dimorphism. I found that this horn dimorphism is affected by larval nutrition (Iguchi, 1998). Another example is that I found mandible trimorphism of male D. rectus, which had been considered to exhibit mandible dimorphism (Iguchi, 2013).

I also found for the first time that both males and females of T. dichotomus exhibit same-sex sexual behavior (Iguchi, 1996). I clarified for the first time that female-female sexual behavior in this beetle species may function as a tactic for reducing intrasexual fighting between small and large females (Iguchi, 2010).

I have also researched geographic variation in the flash pattern and DNA of “Genji botaru” (Japanese firefly, Luciola cruciata) in cooperation with Professor Hideo Kusaoke, Fukui University of Technology. Such geographic variation has already been reported by Dr. Nobuyoshi Ohaba, but its temperature-dependence is not yet fully clear. I have found temperature-dependent geographic variation in flashes of L. cruciata, which is in agreement with molecular biological results by Professor Kusaoke. My recent studies have suggested that this geographic variation is closely related to geological events caused by plate tectonics (see, Geographical variation in the firefly Luciola cruciata in relation to geological events).

I have also studied the morphology of fireflies. One of my studies showed that neither Luciola cruciata nor L. lateralis is likely to conform to Rensch's rule (Iguchi, 2007).

I have been also engaged in the conservation of native fireflies in corporation with Dr. Teruya Mitsuishi, President of Nagano Association for Fireflies Research, because fireflies have been often intentionally introduced into new areas in order to attract many tourists. Such introduced fireflies are considered to threaten biodiversity in the new areas. For example, the intentional introduction of non-native firelies made native fireflies go extinct in Matsuo-kyo, Tatsuno Town, one of the most famous firefly habitats (see Non-native fireflies in Tatsuno for more detailed information). Therefore, we have appealed to the public not to transport and release fireflies without careful consideration.

I have been also interested in exploring psychological traits of human behavior. For example, my collaborative research discovered the effects of goal-setting and self-graphing on math fluency (Onoue, Iguchi and Maruno, 2017).

See Publications for more information on my studies.