Mechanisms determining dominant species in egg parasitoid guilds of the green rice leafhopper, Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae)

Egg parasitoids are important mortality factors in density-regulation mechanisms of the green rice leafhopper Nephotettix cincticeps (Uhler). However, ecological approaches to utilize them for biological control remain limited. In this study, the possible mechanisms that determine species dominance within the egg parasitoid guild, as well as methods for optimizing and selecting these parasitoids for use as biological control agents, were clarified. A total of 3045 N. cincticeps egg parasitoids belonging to six species from seven sites in Japan were reared. Species assemblages were analyzed by clustering, principal correspondence analysis, and distance-based redundancy analysis with 60 environmental variables. The results showed that five climatic and biotic environmental factors, including mean temperature, winter relative humidity, and migratory-planthopper density, influenced species dominance. Paracentrobia bicolor (Girault) (Hymenoptera: Trichogrammatidae) was dominant in coastal areas with high average temperatures and low winter humidity, whereas Gonatocerus cincticipitis Sahad (Hymenoptera: Mymaridae) was dominant in interior regions with contrasting climatic conditions. These findings may facilitate selection of biological control agents tailored to local climates. The results also highlight the importance of small-scale vegetation management within and around paddies for the conservation of both dominant species. Additionally, the study suggests the potential for enhancing egg parasitoid communities targeting planthopper and leafhopper species in fields, as several planthopper egg parasitoids were found to utilize N. cincticeps eggs as alternative hosts.