Life History and Production of Dominant Larval Insects on Stone Dikes in the Lower Mississippi River.

摘要

Macroinvertebrate samples were obtained monthly from stones on dikes in the Lower Mississippi River (river miles 510-515) near Vicksburg, Miss., from September to November 1987 and May to October 1988. The midge Rheotanytarsus sp. and the caddisfly Hydropsyche orris were the dominant epifaunal aquatic insects. Seasonal changes in relative abundance of instars indicated trivoltine and bivoltine life cycles for Rheotanytarsus sp. and H. orris, respectively. Developmental synchrony was high among individuals in both populations. Production-to-average standing crop (P/B) ratios were estimated for each generation of each population based on life cycle, density, and individual dry weight data. The spring, summer, and fall generations of Rheotanytarsus sp. had P/B ratios of 4.2, 4.3, and 3.0, respectively. The spring and late-summer generations of H. orris had P./B ratios of 4.1 and 4.0. These values closely match those in published studies for other midge and hydropsychid caddisfly populations. Annual production of Rheotanytarsus sp. was 344.0 mg (dry weight)/m2. This is the first production estimate for this midge. Annual production of the H. orris population was 10.1 g/m2, a value that closely matches the average value of 12.6 g/m2 based on nine published accounts of highly productive lotic hydropsychid populations on natural cobble riffles. Stone dikes are an important source of stable coarse-grained substrate in the Lower Mississippi River and support high production of rheophilic epifaunal species such as Rheotanytarsus sp. and H. orris. Keywords: Indigenous populations; Ecosystems; Enviromental survey. (kt)