Bionomics of Bembidion confusum (Coleoptera: Carabidae) with Special Reference to its Reproductive Adaptations to the Stream-margin Habitat1

Abstract

Adults of Bembidion confusum Hayward are gregarious and inhabit the immediate vicinity of streams, making small, round holes as temporary shelters. Population numbers, especially those of immatures, depend mainly on quantity of water in the stream. Hibernation is from late October to early April of the following year. Hibernating stages are larva, pupa, and adult. Developmental periods for eggs, larvae, and pupae in spring averaged 7, 60, and 13 days, respectively. Eggs are laid singly three to four per day over a period of 5–6 days. The first batch matured ca. 2 weeks after emergence and the second, 2–3 weeks after the first. Total number of eggs per female per batch was 18–24, depending on number of ovarioles. Food consisted of mud beetle larvae, collembolans, small dipteran larvae, and its own larvae, all breeding in the same habitat. Adults lived 4–8 months, depending on time of emergence. In females, egg resorption took place frequently during dry summer months. Both sexes mate with several different individuals. The spermatheca holds spermatozoa of 4–5 different males simultaneously; sperm are then mixed by contraction of muscles surrounding the spermatheca before fertilization. Thus, there is no priority of sperm from individual males in this species. In males, free spermatozoa developed not in testes, but in vesicula seminales, and spermatogenesis was repeated only in 6–7% of males studied.