Diversity and seasonal dynamics of egg parasitoids of Rinaca japonica in northwestern China reveal Mesocomys trabalae as a dominant biocontrol agent.

BACKGROUND

The economically important walnut tree (Juglans regia) is severely affected by outbreaks of the Japanese giant silkworm (JGS), Rinaca japonica, in northwestern China. To support the development of biological control strategies, we investigated the species composition and population dynamics of JGS egg parasitoids in Longnan, a region heavily affected since JGS spread in 2006.

RESULTS

Between 2018 and 2020, naturally laid JGS egg masses were collected, and 12 parasitoid species across six genera and four families were identified. The dominant species were Mesocomys trabalae (53.64-67.25%) and M. albitarsis (18.30-30.91%). A single JGS egg mass could host up to four parasitoid species, with co-parasitism involving M. trabalae exceeding 70%. From 2021 to 2023, sentinel egg cards were used to monitor the field population dynamics of parasitoids. This activity began in August each year and persisted for >4 months. Mesocomys trabalae was the earliest, most abundant and longest-lasting species. Parasitized eggs from early August to October have the potential to successfully produce parasitoids thereby completing another generation within the same year. Moreover, emergence rates were >90%, with predominantly female offspring (>60%). Temperature positively promoted parasitism, whereas rainfall and its interaction with temperature negatively affected parasitoid activity.

CONCLUSION

This study clarifies the diversity and seasonal dynamics of JGS egg parasitoids, providing essential baseline data for the development of biocontrol agents and mitigation of the risk of JGS spreading into new habitats. © 2026 Society of Chemical Industry.