Newly hatched larvae of Chironomus decorus, Endochironomus nigricans, and Chironomus staegeri mostly from a single shallow eutrophic pond near St. Catharines, Ont., were reared to the adult stage at 15°C and 20°C and 16 and 8 h daily photoperiods. Normal development to EM50 took 26 days at 20°C and 37 days at 15°C in C. decorus; 35 and 48 days in E. nigricans; and 68 days at 20°C in C. staegeri. The 8 h daily photoperiod inhibited emergence, by preventing pupation of final instar larvae, in E. nigricans and C. staegeri at both temperatures, and in C. decorus at 15°C. Nevertheless, a few individuals emerged even under these conditions; such individuals may be important in insuring field populations against environmental variation.

Food supply was normally adjusted to permit only partial emergence even in non-inhibiting regimes. After initial emergence was complete, more food was added to some replicates. In suitable regimes, remaining larvae then completed metamorphosis. Larvae undergoing delayed metamorphosis (for whatever reason) suffered mortality at low food levels; this suggests that food was required for maintenance even by individuals in which metamorphosis was inhibited by photoperiod/temperature combinations alone.

After a further period, when any food-induced emergence had been completed, transfers to higher temperatures or longer photoperiods were made. Transfer after initial inhibition to regimes that normally permitted emergence resulted in emergence; and in E. nigricans transfer at 8 h photoperiod from 15 °C to 20 °C also resulted in emergence, suggesting that the cues for induction and termination of dormancy are not the same, since 8 h photoperiod normally induces dormancy at both temperatures. Emergence after such transfers was more highly synchronized than in the initial period, but protandry was generally retained.