EMERGENCE OF CADDISFLIES (TRICHOPTERA) AND MAYFLIES (EPHEMEROPTERA) FROM HEMING LAKE, MANITOBA

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Abstract
Forty-nine 0.1 m2 emergence traps positioned over several substrate types and a range of water depths 0.9 to 5.5 m, from 2 June to 7 September 1967, collected 979 caddisflies and 195 mayflies. The caddisfly emergence was restricted to the period 24 June −27 August, and mayfly emergence to the period 2–30 July.The sex ratio for the caddisflies showed, in almost every case, a preponderance of females and no male Neureclipsis bimaculatus (Linn.) and N. validus Walk, were collected. Most of the caddisflies showed preference for a particular depth and/or substrate type. The few caddisflies which were present both in large numbers and distributed over a fairly wide depth range indicated that there is a relationship between depth distribution (temperature) and emergence time, heat perhaps being involved both in control of rate of maturation and as a releasing agent for the actual emergence.Male Stenonema interpunctatum canadense (Walker) showed peak emergence about 5 days before the females and also outnumbered the females by about 3:1. No relationship seemed to exist between depth distribution and emergence time for any of the mayfly species. However, the emergence of one species, Caenis forcipata (McD.) may be related to weather conditions.

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