THE BIOLOGY OF TWO RELATED SPECIES OF COENAGRIONID DRAGONFLIES (ODONATA: ZYGOPTERA) IN WESTERN CANADA

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Abstract
The biology ofCoenagrion angulatumWalker andC.resolutumHagen in Saskatchewan has been studied. In these species embryonic development begins as soon as the eggs are laid and is completed in the field within 3 weeks. Larval development is rapid and larvae in the final instar were first collected before the middle of September. Development ceases during the first 2 weeks of October when the water temperature is about 2 °C. By this time the majority of larvae are in the last three instars. Larvae overwinter frozen in the ice 15 to 20 cm below the pond surface. They are able to survive temperatures as low as −5° to −6 °C though these extremes are not normally experienced in the field because of snow cover. Although the study pond filled with runoff water by mid-April no change in the larval population structure occurred until mid-May. Emergence, which is highly synchronous, begins in the last week of May. However, it is governed by the prevailing air and water temperatures, and occurs only when the mean daily water temperature exceeds 12 °C and the mean maximum air temperature reaches 20° to 21 °C. Most insects emerge within 10 days of the first appearance of the adults. Sexual maturation takes about 1 week. Oviposition occurs while the pair are in tandem. Preferred oviposition sites are the submerged portions of stalks of floating plants such asUtricularia,Ranunculus, andPotamogeton. The observations are discussed in terms of the species’ ability to survive the climatic extremes of central Canada.