Assistant professor SAGA Tatsuya of the Graduate School of Human Development and Environment, who is captivated by hornets and is advancing the understanding of their ecology, has an unusual career path, having taught at public high schools for 10 years. After completing a master’s program, he became a high school teacher, took a leave of absence to pursue a doctoral program, and returned to high school teaching after completing his doctorate. During this time, he continued his research independently, and in his mid-30s, he made a fresh start by joining Kobe University to devote himself to research. It has been over two years since he relocated his research base to Kobe. We asked him about the research on hornet ecology he has conducted, the outcomes of this research, and the insights derived on fostering a better relationship between “humans” and “nature.”
Why do queen bees and worker bees exist?
You specialize in the evolution and ecology of hornets, specifically the yellow hornet (Vespa simillima) and the Asian giant hornet (Vespa mandarinia). What kind of research have you been doing recently?
Saga:
I am the type of researcher who works on multiple themes at the same time. One of them is the question of “How are prey species distributed among the queen, males, and (female) worker bees of the yellow hornet?” In the case of honeybees, larvae that are continuously fed royal jelly for a week become queens, while those that are weaned off after three days become worker bees. It is known that whether an individual becomes a worker bee or a queen is determined not by their genes, but by the type of food they are given.
However, in hornets like the yellow hornet, it is still unclear what factors differentiate queens and workers. Is there a difference in the type and amount of food provided? My research aims to apply the insights gained from honeybees regarding food to hornets, to determine if similar mechanisms are at play.
Carnivorous hornets consume many insects. By examining the DNA taken from the contents of the intestines of larvae in exterminated nests, we can determine what types of prey were fed to these individuals. We are testing the hypothesis that there might be a difference in the quality of food given to larvae that become workers and those that become queens. By identifying the types of prey, we can also investigate the biodiversity of insects in the area.
Let me explain the research to some more detail. Workers of social Hymenoptera insects, such as hornets and ants, end their lives by working solely for their nest without leaving any offspring of their own. Despite this, it has been a mystery since Darwin’s time how these traits are inherited through genetics. This phenomenon is explained by the evolutionary mechanism of kin selection, whereby an individual helps its relatives, who share its genes, allowing its own genes to be passed on to future generations through these relatives, without directly leaving offspring of its own. Hymenoptera insects have a peculiar sex determination system where fertilized eggs become females and unfertilized eggs become males. Theoretically, this means that workers share a higher percentage of their genes with the queen than with males, predicting that they would provide more support to the queen. Workers, which do not leave their own offspring, recognize the higher value of queen larvae, with whom they share a closer genetic relationship, and are hypothesized to preferentially give them higher quality food.
It is also known that queens of the wasp known in Japan as “kurosuzumebachi” (Vespula flaviceps) mate with multiple males (2 to 7) in fall. The more times the queen mates, the less closely related the worker bees are to the next queen, leading us to hypothesize that the quality of food given to the larvae may decrease. We are investigating how the types of food differ. We believe that the value of the queen itself varies from nest to nest.
A new method for monitoring biodiversity
What are the research projects you are conducting in parallel?
Saga:
Another project focuses on the theme of “Establishing a biological survey method through the analysis of the diet of hornet species.” Hornet and paper wasp nests are actively exterminated and discarded throughout the country. However, by examining the food consumed by the larvae in the collected nests, we realized that it is possible to monitor the biodiversity of the area and determine how many different species are present.
There is a nationally certified sustainably managed natural site, certified by the Ministry of the Environment, in the Kita Ward, Kobe City, where biodiversity monitoring of flora and fauna is required. Since the hornet nests around this area are also being exterminated, we believe that by analyzing these nests we can investigate the number of species in this region, which is already recognized for its high biodiversity, although this method has the bias of reflecting what the hornets consume. In the 2023 survey, the DNA of the invasive carpenter bee Xylocopa tranquebarorum was detected in the intestines of hornet larvae. This species was first reported in Hyogo Prefecture in 2016. I believe this monitoring method is also effective for confirming the existence of non-native species.
I have already completed the preliminary research and established the method. I am currently conducting research to implement a method of understanding regional biodiversity from the diet of hornets as a practical application.
The need for biodiversity monitoring is increasing in Amami Oshima, Tokunoshima, the northern part of Okinawa Island, and Iriomote Island, which have been registered as World Natural Heritage sites in 2021. In these areas, information about the introduction of invasive species is very important. Also, even though they are registered as World Natural Heritage sites, we do not fully understand which areas have high biodiversity and where endangered species reside. By using hornets as surveyors, we plan to establish a method to investigate the variety of species in the area, including invasive species, through regular observation of the region.
Japan’s DNA database is quite advanced by international standards. Approximately 150 types of DNA have been detected from the intestines of the larvae of yellow hornets in Kobe City. Around 100 types of DNA have also been found in the yellow-vented hornet (Vespa analis). Another study conducted on the southern and northern slopes of Mount Rokko, which divides Kobe City, revealed that, from the perspective of the hornets, the southern side has about half the number of prey species compared to the northern side.
In 2008, the “Basic act on biodiversity” was enacted.
Saga:
With the enactment of the “Basic act on biodiversity,” the conservation of biodiversity has become a responsibility that national, prefectural and municipal governments must undertake. Private companies and individuals are also required to make conservation efforts. However, the methods for actually investigating biodiversity are still insufficient.
Professor MINAMOTO Toshifumi of the Graduate School of Human Development and Environment at Kobe University has established a detection method that identifies the types of organisms present by examining DNA in rivers, ponds and seawater. He is a pioneer in this field.
However, methods for monitoring terrestrial biodiversity are still far from being established. Surveying the presence of various organisms in jungles like those on Iriomote Island requires considerable effort, and attempting to conduct such monitoring would require highly impractical budgets. We are currently exploring ways to address these challenges. If the current hornet-based biodiversity monitoring proves to be effective to some extent, I would like to explore how it can contribute. The significance of the contribution will be revealed through this research.
It also depends on how much cooperation we can get from the municipalities that subsidize extermination. If we can establish a process for extermination, collection and analysis, this could form a method for biodiversity monitoring. Implementing this on a societal level will require the cooperation of municipalities and society as a whole.
Touching on the culture of eating hornets
Why did you start researching the ecology of hornets?
Saga:
I am a first-generation student of the Faculty of Applied Biological Sciences at Gifu University. During my third year, I had the opportunity to participate in a 13-night, 14-day camp in the mountains, where I collected Asian giant hornets. Seeing the hornets at that time, I thought, “They look so cool,” and chose them as the theme for my graduation research. That was the beginning of my research.
When I was a high school teacher in Gifu Prefecture and studied by my own, I noticed that people in the mountainous areas of the Tokai region liked to eat kurosuzumebachi and Asian giant hornets. This has been established as a culture and I was impressed by their pursuit of how to catch them, how to eat them, and how to make hornets delicious, which led me to delve further into hornet research. In Ina Valley in Nagano, for example, the larvae of the black hornet are called “hachi no ko” and were always served at weddings in the past. In addition, in the Tono area of Gifu Prefecture, it is still used as an ingredient for a local sushi dish called “hoba sushi.” It is used as a festive food. Hornets are still sold for about ?12,000 per kilogram, positioning them as a delicacy along with “matsutake” mushrooms and eel. The more I learned, the more interesting it became.
In China, the culture of eating insects is still accepted and continues today. In Japan, in 1919, entomologist MIYAKE Tsunemasa conducted a survey on insect consumption through agricultural and forestry experiment stations nationwide and found that all the municipalities that responded reported eating insects. Hyogo Prefecture also had this food culture. It is only recently that insect consumption has declined in Japan.
As people stopped eating insects, they developed a strong aversion to insects, and extermination became more active in those areas. On the other hand, those who eat hornets trade them at very high prices and enjoy them as a delicacy. It seems for me that those who continue to eat hornets have a greater respect for their country’s culture. This shift in perspective — from wanting to research hornets simply because they are fascinating to considering their cultural and ecological value — was a significant motivation to continue my research independently.
I also collect and eat hornets as a seasonal delicacy in fall. Generally, information about hornets and paper wasps tends to emphasize that they sting, cause pain, are scary, and can even be fatal to humans. While this is important, I believe that fear often comes from a lack of knowledge. By continuing my research and clarifying their ecology, I hope to change society’s perception of hornets. I want to show that hornets are not pests but beneficial insects.
From high school teacher to researcher
You went from high school teacher to the doctoral program, then back to teaching, and eventually arrived at Kobe University.
Saga:
Ideally, I would have gone straight into a research career. However, during my first year of university, a family tragedy occurred and I considered dropping out of university. But an encounter with hornets in my third year inspired me to continue my studies while working part-time, eventually completing my master’s program.
Wanting to work with living organisms, I chose to become a high school teacher. I worked for four years to save up for tuition, and when a program for working professionals to pursue a doctorate was launched in Gifu Prefecture, I took a leave of absence to return to the university research environment, where I immersed myself in research to my heart’s content.
While ordinary citizens continue to pass on the culture of eating hornets, there are also those who believe that exterminating and killing them is the right thing to do. Finding this relationship between these fascinating creatures and humans intriguing, I chose to work in Gifu Prefecture, where the culture of eating hornet larvae exists, even after completing my doctoral program. I continued my independent research while eating hornet larvae and interacting with the local people. Two years ago, I was fortunate to have the opportunity to conduct research at Kobe University. My life has indeed been greatly influenced by hornets.
Why Kobe University?
Saga:
The Graduate School of Human Development and Environment, where I work, may not clearly indicate what kind of research is being conducted just by its name. Wanting to conduct the kind of research I am doing now, I realized that it didn’t quite fit in with an agricultural faculty, a science faculty, or a literature faculty. So, I continued to do research as I pleased while working as a high school teacher. I thought it would be good to take up the challenge if I could conduct comprehensive research that integrates both human and environmental aspects. Now that I am here, I am glad that it is a faculty that allows me the freedom to pursue my ideas. The university’s ethos matches my own very well. In these two years, I have been able to incorporate six or seven research themes and do the research as I envisioned.
Kobe City is a very advanced city in terms of the “Basic act on biodiversity.” The first nationally certified sustainably managed natural site recognized by the Ministry of the Environment is also in the Kita Ward of Kobe City. I am very grateful to be able to work at Kobe University, which is located near this site.
Understanding humans is also a research area
Are there any other interesting studies on hornets?
Saga:
It is generally accepted that hornets should not be eaten in the summer and that fall hornets are the most delicious. However, no one in the world has studied it from the perspective of taste. We are currently conducting joint research with researchers specializing in nutritional science from various universities in Japan to determine how fall hornets are superior as a food ingredient. Understanding the origins of the culture of eating hornets through scientific means is the most fascinating aspect for me right now.
What are your future research plans?
Saga:
I would like to continue my research at the Graduate School of Human Development and Environment to learn more about hornets and kurosuzumebachi. I am interested in understanding the relationship between hornets and humans, and more broadly, the interaction between humans and living organisms.
To understand this, I believe I need to know about both hornets and humans. I have acquired various methods to study hornets to a certain extent. Although I have worked with people as a high school teacher, my approach was self-taught. Therefore, I hope to learn from my colleagues about research methods for understanding human beings. Moving forward, it would be my greatest wish to elucidate the relationships between humans and nature and between humans and hornets.
Resume
| March 2008 | Graduated from the Faculty of Applied Biological Sciences, Gifu University |
| March 2010 | Completed the master’s program, Gifu University |
| April 2010 | Full-time lecturer, Department of Agriculture of Gifu Prefectural Gifu Senior High School of Agriculture and Forestry |
| April 2011 | Full-time science teacher, Gifu Prefectural Ogaki Sakura High School |
| March 2017 | Completed the doctoral program, Graduate School of Arts and Sciences, University of Tokyo |
| April 2017 | Full-time science teacher, Gifu Prefectural Tajimi High School |
| August 2019 | Special cooperative researcher, Faculty of Applied Biological Sciences, Gifu University (concurrently) |
| December 2022 | Assistant professor, Graduate School of Human Development and Environment, Kobe University |
