Life History and Energetics of Ancyronyx variegata (Coleoptera: Elmidae) in Northwest Arkansas and Southeast Texas

Larvae and adults of Ancyronyx variegata (Germar) were collected monthly from the White River and Illinois River in northwest Arkansas, and from Harmon Creek in southeast Texas. In both locations, A. variegata showed a univoltine life cycle of 6 larval instars. Field data combined with laboratory rearing indicated that the cohort production interval was ≈353 d. Growth rate of the larvae was similar in both locations. The main periods of recruitment were April and May in Arkansas, and March and April in Texas. However, 1st instars were present in at least small numbers in both locations during most months. Egg incubation took ≈14 d. Sixth-instars crawled out of the water on submerged wood and pupated in wood that was moist but not saturated; emergence began ≈14 d after pupation began. Adults were present in both locations during the entire year, indicating that adults probably have extended life spans. Annual production was 1.78 g/m2/yr, mean standing stock biomass was 0.54 g/m2, and the cohort production/biomass ratio was 3.31 in Arkansas. In Texas, annual production was 0.98 g/m2/yr, mean standing stock biomass was 0.20 g/m2, and the cohort production/biomass ratio was 4.82.