The Microdistribution and Population Trends of Larval Tanypus Stellatus Coquillett and Chironomus Frommeri Atchley and Martin (Diptera: Chironomidae) in Utah Lake, Utah

The microdistributional patterns and life histories of larval Tanypus stellatus and Chrionomus frommeri were studied in Goshen Bay of Utah Lake, Utah, from July 1973 to August 1974. Vertical distribution data shown that over 90% of the larvae were located in the top 7.5 cm of the substratum. Depth of penetration into the substratum increased with the later instars. Chironomus frommeri larvae penetrated deeper than those of T. stellatus. Biomass was distributed bimodally. The mode at the 0—2.5—cm depth was due to high numbers of early instar larvae. The second mode, at the 17.5—20.0—cm depth was due to the presence of fourth instar C. frommeri larvae. Tanypus stellatus showed a contagious distribution in the early instars with a trend towards randomization with age. Larvae of C. frommeri rarely showed contagious distributions. This was likely related to their low abundance in the samples making detection of a contagious distribution difficult. The larvae of T. stellatus overwintered in the first and second instar. This overwintering generation emerged in early July and gave rise to a second summer generation which emerged in August. Chironomus frommeri overwinter mainly as third and fourth instar larvae. Emergence occurred throughout the summer although two strong emergence pulses were seen, one in May and the second in July—August.