Summary: Freshwater Biology (1986) 16, 155-159
Diel activity of a boreal water beetle (Dytiscus ahskanus:
Coleoptera; Dytiscidae) in the laboratory and field
R. B. AIKEN Department of Entomology, University of Alberta,
Edmonton, Alberta, Canada
SUMMARY. 1. The diel activity of Dytiscus alaskanus (Coleoptera:
Dytiscidae) was studied by trapping in the field and by direct observa-
tion of behaviour (mounting, chasing, grappling, swimming and surfac-
ing) in the laboratory.
2. In the field, the number of beetles trapped during the dark hours
was approximately fifty-fold greater than trapped during daylight hours.
3. In the laboratory, there was a marked increase in mounting,
chasing and grappling when the ambient light level fell below 0.4 Im m"^.
Swimming showed only a slight diel pattern and surfacing none at all.
Virtually all insects, except perhaps those in
caves, respond in some way to temporal
periodicity in their environment. One aspect of
this periodicity that has received the attention
of a great number of authors is diel periodicity