Oviposition of Hydropsychidae (Trichoptera) in a large river

Abstract

Scuba observations in the Susquehanna River revealed that oviposition of Cheumatopsyche speciosa and Hydropsyche phalerata began 26–44 min (mean, 33 min) after sunset and lasted for 19–30 min (mean, 24 min). Females oriented into the current on acrylic plates and ociposited in 30–60 s. Cheumatopsyche (probably C. speciosa) and H. phalerata egg masses contained a mean of 265 (134–504) and 367 (116–679) eggs, respectively; masses were largest and most densely packed with eggs in mid-June. Cheumatopsyche egg masses (84% of the 15 000 hydropsychid masses collected in 1981) were found from 21 May to 30 September; up to 980 egg masses∙m−2∙day−1 occurred in mid-July. Hydropsyche phalerata egg masses (15% of the total) were found from 22 May to 14 September; up to 170∙m−2∙day−1 occurred in early June. Both species oviposited almost daily when river temperature exceeded 15 °C. During a 30-day period when river temperature and depth were stable, there was a highly significant (P < 0.01) positive correlation between the number of Cheumatopsyche egg masses and evening air temperature. Positive correlation between the number of egg masses and river current (10–47 cm/s) at eight sites was highly significant (P < 0.01) for H. phalerata but not for Cheumatopsyche (P > 0.05). Hydropsychid egg masses were widely distributed over an acrylic hemisphere in a slow (15 cm/s) current but were concentrated on the top, downstream portion in a strong (58 cm/s) current.