BENTHIC AND LIMNETIC DISTRIBUTION OF THREE CHAOBORUS SPECIES IN A SOUTHERN MICHIGAN LAKE (DIPTERA, CHAOBORIDAE)

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Abstract
The benthic and limnetic distributions, and size‐frequency, of the overwintered larval populations of three Chaoborus species, C. punctipennis (Say), C. albatus Johnson, and C. flavicans (Meigen) in Frains Lake, Michigan, were investigated on three dates in May and June 1965. The three species made up 91, 3, and 6% of the Chaoborus fauna. Little overlap in total length was found between species. C. flavicans tended to be concentrated in deeper benthic zones during the day than C. punctipennis. C. albatus, but not the other two species, underwent an adlittoral benthic migration. All three species migrated into the limnetic zone at night, but none reached the surface. Most limnetic C. punctipennis larvae were found higher in the water column than C. flavicans larvae.The larvae of C. albatus were stunted, showed late growth, and may have been unable to avoid competition with larvae of the closely related C. punctipennis. Differences in distribution and morphology between C. flavicans and C. punctipennis, although slight, help to explain the apparent lack of competitive exclusion in this genus.