A survey on larvae of Japanese wasps revealed that not only is their diet more diverse than previously thought, it also showed that wild colonies prey on more species of vertebrates than had been reported in the past. The Kobe University study highlights the potential for management practices that are sustainable both ecologically and culturally.
The wasp species Vespula shidai has long been reared for its edible larvae, a delicacy in central Japan. The rural woodlands of Japan which these wasps inhabit are areas of high biodiversity. Though this practice of rearing and consuming V. shidai larvae, known locally as hachinoko, has existed for decades, there is little knowledge on the difference in feeding habits between those that have been reared by humans and those that have been harvested in the wild, with only fragmentary updates since the mid-1950s. Now, advancements in genetic techniques have provided a clearer picture of the wasp's dietary habits.
Kobe University entomologist SAGA Tatsuya and his team performed a study on the gut contents of larvae found in both wild and reared nests using DNA metabarcoding, a technique that can identify multiple species from a single sample. Saga says, "The research idea was inspired by my firsthand experience of eating the larvae of the giant hornet without removing the intestines and seeing that the intestines are filled with various creatures. As the beetle fragments jiggled in the mouth, I thought that examining the intestines will reveal what the wasps are eating."
The results of this study, published in the Journal of Insects as Food and Feed, found that the wasps preyed on 324 different, including insects, arachnids, birds, mammals, reptiles, amphibians and fish. Although most nests from both subsets were shown to feed on mostly birds and mammals, the results showed significant differences in prey composition between wild and reared nests. In particular, a far greater variety of vertebrate species were captured in wild nests, suggesting that nutrient-rich vertebrate carcasses are vital to the wasps' development. That said, both wild and reared nests showed similarly high levels of captured insect species, implying that wasps may retain their potential role in insect population control even under rearing conditions. What this also indicates is that reared wasps seem to be less reliant on wild carrion, which has the potential to alter carrion dynamics and alter the local scavenging ecosystem.
While DNA metabarcoding was necessary to identify specific species contained within the gut of the larvae, the difference in prey composition between the wild and reared subsets was so pronounced that those with extensive rearing experience could even taste it. As part of this study, a questionnaire survey was given to consumers of hachinoko, in which 58% of respondents with rearing experience answered that not only could they taste the difference, they often preferred wild hachinoko to their reared counterparts based on flavor and aroma. However, further studies are required to clarify the effects of rearing experience on taste perception.
On the significance of this research, lead researcher Saga says, "In recent years, food products based on indicators such as low environmental impact and high production efficiency have been the focus of attention, but I was made keenly aware once again of the value of a culture in which humans have lived in and interacted with nature and fed on its creatures." This study, which integrates scientific insights and cultural traditions, is vital to ensuring both the ecological mindfulness and viability of wasp rearing, while also highlighting the potential for management practices that are both culturally informed and promote ecological sustainability. As this study was conducted exclusively in the autumn and with relatively few nests in a limited area, future studies should expand to different regions and seasons while further investigating social and cultural factors affecting feed choice to guide sustainable management of this unique delicacy.
This research was conducted in collaboration with researchers from Okayama University.
Kobe University is a national university with roots dating back to the Kobe Higher Commercial School founded in 1902. It is now one of Japan's leading comprehensive research universities with nearly 16,000 students and nearly 1,700 faculty in 11 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society's challenges.
