A 7-year life cycle for two Chironomus species in arctic Alaskan tundra ponds (Diptera: Chironomidae)

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Abstract
The life cycles of 2 sibling Chironomus spp. inhabiting tundra ponds on the arctic coast of Alaska are interpreted from larval and adult data collected over 3 years. Emergence of adults was highly synchronous within each species, and the 2 emergence periods were always discrete. Larvae of the 2 spp. could not be separated morphologically and were treated as a single population through most of the life cycle. Analysis of larval size and development toward pupation indicated that 7 cohorts coexist on nearly all sampling dates. A 7-yr developmental period for each cohort is hypothesized and is supported by larval growth rates observed in the habitat and by the rates at which apparent cohorts progressed through the larval stages. Ten cohorts observed during the study period showed very similar schedules of growth and development, but cohort abundances varied considerably. This life cycle is among the longest reported for an arctic insect. It results from slow growth during an annual open-water season of about 90 days, though neither food nor temperature limitation could be definitely implicated in causing such slow growth. Coexistence of up to 7 cohorts in each species stabilized Chironomus production and standing stock and may be important to benthic-feeding waterfowl which use these ponds.
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