EFFECTS OF PREDATORS AND FOOD AVAILABILITY ON ACTIVITY AND GROWTH OF CHIRONOMUS-TENTANS (CHIRONOMIDAE, DIPTERA)

1. Larvae of Chironomus tentans Fab. decreased the amount of time they spent outside their tubes as the presence of predatory pumpkinseed sunfish (Lepomis gibbosus L.) increased. Greatest reductions in activity occurred at low levels of fish presence; above a certain level further increases in fish presence had little effect on activity. 2. Whether the pattern of predator presence was ordered or random had no effect on larval behaviour. Larvae did not habituate to short- or long-term predator presence. 3. Larvae were less active when more food was available and predator-induced reductions in activity were negatively related to food availability. Larval activity was much higher in the dark than it was in the light. 4. Over 7 days, presence of fish reduced the proportion of third-instar larvae that moulted but did not affect head width or dry mass; low food availability reduced the number of larvae that moulted as well as head width and dry mass of larvae in the fourth instar. 5. Results indicate that the behavioural response of larval chironomids to predator presence depends strongly on environmental conditions and that estimating the developmental costs of these behavioural responses under field conditions will be complicated.