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Influence of Stream Temperature and Seston on the Growth and Production of Overwintering Larval Black Flies (Diptera: Simuliidae)

Merritt, Richard W., Ross, Douglas H., Larson, Grahame J.
Ecology 1982 v.63 no.5 pp. 1322-1331
Prosimulium mixtum, Stegopterna, confidence interval, diameter, equations, instars, larvae, larval development, overwintering, spring, streams, univoltine habit, water temperature, winter, Michigan
The influence of stream temperature and seston on larval growth and production of the univoltine black flies Prosimulium mixtum Syme and Davies, P. fuscum Syme and Davies, and Stegopterna mutata (Malloch) was studied in a southcentral Michigan first—order stream. Black files were sampled quantitatively with artificial substrate for production estimates and qualitatively estimate instar—specific dry mass. Length—mass equation obtained for each species and most instars indicated that maximum growth occurred in the later stadia. Production estimates (as dry mass per square metre of artificial substrate, with 95% confidence interval) for two cohorts of P. mixtum/fuscum were 696 ± 95 and 1939 ± 339 mg°m— ²°yr— ¹. On artificial substrates, mean standing stock biomasses for the two cohorts were 110 and 507 mg/m², and the cohort P/B ratios were 6.32 and 3.83, respectively. Seston concentration (AFDM) during the winter and early spring were highly dependent on stream discharge and ranged from 0.81—8.33 mg/L, with a mean of 3.73 mg/L. Particles <45 μm comprised >92% of the total organic seston, and larvae ingested particles in the 0.45—45 μm size class almost exclusively, with 85% of the particles in larval guts <10 μm in diameter. No significant differences existed in the size frequency distributions of particles in the guts among instars or between species, suggesting that the quantity of seston in the 0.45–45 μm size class was not limiting. Over 81% of P. mixtum/fuscum annual production occurred during the last two larval stadia and was attributed to increases in stream temperature and seston organic content during the late winter and early spring.