Life history patterns of stream-dwelling caddis

Abstract

With 13 figures and 3 tables Abstract: Full life histories of fourteen coexisting species of caddis in an Irish stream are described. The study is based on growth patterns and distribution of larval head capsule width through time. It also notes adult fl ight periods. Most species had simple life histories and were univoltine (Agapetus fuscipes, Hydropsyche sUtalai, H. instabi lis, PhUopotamus montanus, Ecclisopteryx guttulata, Glossosoma conformis, Drusus annulatus, Po tamophylax cingulatus and Halesus radiatus). In the latter four species the occurrence of instar-l larvae indicated that egg hatching was delayed or prolonged over several months. Complex univoltine life histories were found in three species (Serieostoma personatum, Plectrocnemia conspersa and Silo pallipes) where, gener ally, a one-year life cyc1e occurred, although some individuals required more than one year to emerge. Data for two species (Rhyacophila dorsalis, Odontocerum albicorne) suggested the possibility of bivoltine life histories. Both types of complex life history led to overlapping generations. This is the most comprehensive information to date on the life histories of most of the species. Intraspecific variation in development rates, the wide range of size c1asses present at one time, the ability to overwinter in differ ent larval stages and the asynchronous extended flight periods may be evidence of a "spreading of risk" within life histories. Without knowledge of whether the variations in development rates are genetically determined, it is difficult to advance a hypothe sis based on an adaptive strategy to explain such variation as opposed to attribution to environmentally-controlled variation in growth, influenced by such factors as temper ature and food.

Caddis larvae (Trichoptera, Hydropsychidae) indicate delaying recovery of a watercourse polluted by pulp and paper industry

“…in the last instar. H. siltalai, on the other hand, overwinter mainly as the third or fourth instar, and flies later in summer (Hildrew and Edington, 1979;Sangpradub et al, 1999). In 2008, however, sampling was done in early June which does not explain the absence of H. pellucidula and C. lepida in the Kuusaankoski rapids.…”

Key themes in the study of seasonal adaptations in insects II. Life-cycle patterns

“…Recent examples across various time frames include variable duration of pupal development in a geometrid moth (Tammaru et al, 1999), variable egg hatch of a bushcricket (Hockham et al, 2001), variable larval duration in a burnet moth (Wipking and Kuntz, 2000), and alternative routes among directly developing, dormant and mobile forms in a glycyphagid mite (Knülle, 2003). Sangpradub et al (1999) found intraspecific variation in development rates, a wide range of simultaneous size classes, an ability to overwinter in different larval stages, and asynchronous extended flight periods in caddisflies from a temperate stream. Neal et al (1997) interpreted the variable spring egg hatch of Malacosoma (which was independent of spring temperatures) as a means to offset potential losses of young larvae from late winter storms.…”

Mineral grains in caddisfly pupal cases and streambed sediments: assessing resource use and its limitation across various river types

“…Firstly, the size of the benthos area sampled was perhaps too coarse to detect the segregation of species into microhabitats of the size inferior to that of cobble (e.g., top vs. bottom of a stone; Hildrew and Edington, 1979). Secondly, perhaps to avoid competition, pupal casebuilding periods can be temporally segregated (at least in parts), which has been reported for co-existing species in the genera Hydropsyche and Rhyacophila (Hildrew and Edington, 1979;Ce´re´ghino et al, 1997;Sangpradub et al, 1999). In combination, these two reasons potentially created so much noise that the signal of an actually existing competition among co-existing RCWs could not be detected.…”

“…Confirmed species identifications of larvae are currently often impossible in this species group (Waringer and Graf, 1997), making it difficult to identify prepupae and immature pupae to species. The life cycle of Rhyacophila species is often untypical, as prepupae and pupae can be found spread over many months of the year and the data suggest that their builders use the pupal case for y 2-5 months (Ce´re´ghino et al, 1997;Sangpradub et al, 1999).…”