Chaoborus prey capture efficiency in the light and dark1

The strike efficiency of fourth-instar Chaoborus punctipennis larvae on different size co-pepods was measured in the light and dark in the laboratory. Dark measurements were made with near-infrared illumination and a closed circuit television system. There was no signifi-cant difference between strike efficiency in the light and dark during either day (0900-1800) or night (2100-0600). Strike efficiency generally increased as the prey size decreased, and the longest prey captured was about 1.4 mm. However, 29 % of the larvae which contacted egg-bearing female copepods longer than 1.4 mm ingested all or part of the female’s egg sac. The lack of a measurable difference in larval strike efficiency in the light and dark suggests that the diel vertical migration pattern followed by Chaoborus larvae is not related to diel changes in prey vulnerability.-Recent investigators of vertical migra-tion have attempted to establish the adaptive value of particular migration patterns. The theories of the adaptive val-ue of vertical migration based on ener