Effects of Temperature and Photoperiod on Larval Development in Lestes Eurinus (Odonata: Lestidae)

Eight larval collections of the damselfly Lestes eurinus were made from October 1965 through May 1966. In each collection, eight groups of larvae were subjected to combinations of temperatures (15°, 20°, 25°, 30°C) and photoperiods (11 , 14 hr) until emergence. Using a unique lake facility, three additional groups of animals were subjected to 11—hr, 14—hr, and natural photoperiods all at natural temperatures. At every temperature, larvae completed their development more rapidly when subjected to the 14—hr day. The greatest differences in photoperiodic responses were observed at 20°C. In general, rates of larval responses were progressively faster at higher temperatures, but higher temperatures (25°C, 30°C) did not induce a faster rate for long—day animals. Both field and laboratory observations indicated that each of the later instars had a higher thermal coefficient for growth than that of the preceding instar. Rising vernal water temperatures induced a degree of synchrony into molting and emergence, and were, collectively, a most important factor in seasonal regulation. Quantitative data are presented for the first time in support of Corbet's LTT hypothesis of seasonal regulation in a summer species of Odonata. The separate and combined effects of temperature, photoperiod, and degree of maturity on the developmental rate of larvae are discussed.