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A quantitative study of the life cycle of the case‐building caddis Odontocerum albicorne (Trichoptera: Odontoceridae) in a Lake District stream
Author(s) -
ELLIOTT J. M.
Publication year - 1982
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1982.tb00619.x
Subject(s) - instar , pupa , hatching , larva , zoology , biology , population , ecology , degree (music) , demography , physics , sociology , acoustics
SUMMARY.Odontocerum albicorne (Scopoli) took 1 year to complete its life cycle in a 3‐year study of this species in a small, stony stream in the English Lake District. Adults were present from May to August (1967, 1968) or from June to September (1969); most eggs were laid in July and August. There were five larval instarsand most larvae were in instars III, IV and V by October. Larvae usually overwintered in instar V or III and some third instars were in a resting state in sealed cases. Most fifth instars became male pupae in spring; most third instars grew rapidly to instar V in spring and then became female pupae. The duration of the pupal stage was short, and was shown in laboratory experiments to require 87.5 degree‐days (95% C L = 79–98 degree‐days) above a threshold temperature of 6.7±0.01°C. Pupation in the stream did not commence until temperatures exceeded 6.8°C. As the sample variance‐mean relationship followed a power‐law, the spatial distribution of larvae and pupae was density dependent. Relative clumping remained fairly constant between year‐classes but increased markedly between the larval and pupal stages. Although population density varied between year‐classes, it remained remarkably constant in each year‐class for about 9 months between the end of egg hatching and the start of adult emergence. The growth pattern was similar in each year‐class but growth rates varied between year‐classes. The mean instantaneous growth rate was highest (range 3.9–8.0% dry wt day ‐1 )in the first 3 months of the life cycle (August‐October), close to zero in winter (November‐February) and slightly higher than 1% day ‐1 (range 1.1–1.7%) for the rest of the life cycle (March‐August). Production varied considerably between years and year‐classes, and was closely related to growth rates for March‐August. Annual production estimates were 243, 160 and 257 mg dry wt m ‐2 in 1967, 1968 and 1969. respectively. The ratio of production to mean standing crop (P/B) also varied between year‐classes and the mean annual value was 3.9 (range 3.2–4.5). Life tables were similar for the 1966 (latter part only), 1967, 1968 and 1969 year‐classes. Losses were very high (c. 99%) in the egg stage and early instars. About 30% (range 27–31%) of the population in instars III‐V did not reach the pupal stage, and c. 25% (range 20–29%) of the pupal population died. About 37% (range 35–39%) of the emerging adults were females.