Seasonal Abundance of Adult Caddisfly (Trichoptera) in the Middle Reaches of the Shinano River in Central Japan

Abstract:
Mass emergences of adult caddisflies often lead to severe nuisance conditions. The objective of this study is to clarify the abundance and seasonal trend of adult caddisflies in the middle reaches of the Shinano River. All of the adult caddisflies attracted to the illuminated showcase of a vending machine set along the river were collected with an insect aspirator from 20:00 to 20:20 (20 minutes), every night from March 28 to December 1 in 2006. A total of 2,930 adult caddisflies was collected from May 1 to November 10. The daily abundance of the total adults reached a maximum on September 2 (291 individuals / 20 minutes / m2). We identified a total of 15 species belonging to 12 genera of 10 families. The sex ratio of the adult caddisflies was female-biased during the study period. The most abundant family was Psychomyiidae (83.1%), followed by Hydropsychidae (11.2%) and Hydroptilidae (1.7%). The highest number of species among the families was found in Hydropsychidae (5 species), followed by Psychomyiidae (2 species). The most abundant species was Psychomyia acutipennis (83.1%), followed by Hydropsyche orientalis (5.8%) and Hydropsyche setensis (2.8%). P. acutipennis adults were collected from mid-May to late October and its daily abundance showed two peaks. Adult hydropsychid species were collected from early May to early November. H. setensis was collected from May to September, and its seasonal abundance showed two peaks. Cheumatopsyche brevilineata, Cheumatopsyche infascia and H. orientalis were collected from May to October, and each of their daily abundance showed one peak. Potamyia chinensis was collected from May to October. There were significant correlations between the daily abundance of total caddisflies and daily mean air temperature. No adult caddisflies were collected on the days when the daily mean air temperature was less than 10.7°C.