Behavioral Differences Between 3rd and 4th Instars of Chaoborus punctipennis Say

Abstract

The diel vertical migrations of Chaoborus punctipennis Say (Diptera: Culicidae) were studied during two 24-hr sampling periods at Saratoga Lake, New York. Samples were taken at the surface, 4 and 8 m every 3 hr from 0700 to 1900, then every hour until 0600. A total of 33,349 larvae were collected during sampling, and each of these was categorized according to instar. The temporal distributions of the mature larvae (3rd and 4th instars) were analyzed to demonstrate pos- sible behavioral differences. There was a significant distributional difference for the mature larvae of Saratoga Lake. The behavior of the 3rd and 4th instars was similar until midnight. After midnight the 4th instars consistently showed a secondary peak in numbers while the 3rd instars failed to recover and decreased until sunrise. This decrease can be attributed to the fact that the 3rd instars leave the surface earlier and apparently reenter the sedi- ments sooner than the 4th instars. Two physiological factors (food requirements, and oxygen require- ments) are discussed as possible causes for this behavioral difference.