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Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Life Histories
The life history of a Dipteran (Scathophagid: Acanthocnema) predator of macroinvertebrate egg masses in two northern California streams
A.H. Purcell1, A. Hoffman2, and V.H. Resh1.1University of California, Berkeley, Department of Environmental Science, Policy, and Management, 2Department of Economics, Otto-von-Guericke University, Magdeburg, Germany
The habits and characteristics of an undescribed predator (Diptera: Scathophagidae: Acanthocnema) and its egg mass prey were examined over a three–year period in two northern California streams. Attached egg masses of aquatic insects along with eggs and larvae of Acanthocnema predators were collected regularly within a 200–m reach in Redwood Creek and Webb Creek (Marin County, CA) and reared in the laboratory. This species of Acanthocnema is a generalist predator with a bivoltine life cycle. The winter cohort of the Acanthocnema larvae fed exclusively on Neophylax rickeri (Trichoptera: Uenoidae) egg masses, while the spring cohort fed on several different egg masses, including those of other Trichoptera (Brachycentridae) and Diptera (Ceratopogonidae, Chironomidae). The number of Acanthocnema eggs within each N. rickeri egg mass ranged from 0–11, while the number of Acanthocnema larvae found within each N. rickeri egg mass ranged from 0–19. The duration of the egg stage of the Acanthocnema predator was 2 ± 1 (mean ± sd) days, their three larval instars each lasted 10 ± 3 days and their pupa 90 ± 13 days. Egg consumption rate of N. rickeri eggs by Acanthocnema larvae averaged 9.5 eggs per day.
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