Lestes disjunctus, L. unguiculatus, and L. dryas diapause late in embryogenese when the embryo is almost fully formed. Lestes congener enters diapause just before blastokinesis. Lestes disjunctus, L. unguiculatus, and L. congener undergo a primarily temperature-controlled phase of diapause development, which proceeds most rapidly at 10 °C. In the field it is completed in most eggs by the end of October in L. disjunctus and L. unguiculatus, and by the end of November in L. congener. Subsequent development in L. disjuncius and L. unguiculatus is inhibited by photoperiods shorter than 12 to 14 h. There apparently is some overlap between the temperature- and photoperiod-controlled phases. The inhibitory effects of short photoperiods gradually disappear during the winter. In L. congener there is no significant photoperiod-controlled second phase of diapause. Diapause development in L. dryas probably is similar to that in L. disjunctus and L. unguiculatus.
Lestes congener Hagen overwinters in the egg stage. There is a diapause just before blastokinesis, during which the egg is extremely resistant to low temperatures and desiccation. Post-diapause embryonic development can occur near 0 °C but will not take place until the eggs are wetted as the pond habitat fills in the spring. Hatching does not occur until the temperature exceeds about 5 °C and is highly synchronous. Larval development is rapid and is completed in the field in about 50 days. Emergence of the adults also is synchronous. Sexual maturation requires 3 weeks. Oviposition occurs immediately after copulation while the pair are still in tandem. It takes place only in dry stems of Scirpus. Adaptations of L. congener for life under rigorous prairie conditions are discussed.
Can. Ent. 106: 1277-1282 (1974) A key to macrotype tachinid eggs, actually or potentially occurring on larvae ofHeliorhis spp. in North Carolina, is provided, based primarily on eggs from reared and trapped gravid adults. This key is probably valid for most of the southeastern United States. Eggs of Winthemiini are described (the common Heliothis parasites Winthemia rufopicta (Big.) and W . sinuata Reinh., and also W. manducae Sabrosky and DeLoach, W . datanae (Tns.), and Nemorilla pyste (Walk.)).
Can. Ent. 107: 119-128 (1975) The biology of Coenagrion angulaturn Walker and C . resolutum Hagen 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 as Utricularia, Ranunculus, and Potamogeton. The observations are discussed in terms of the species' ability to survive the climatic extremes of central Canada.
The latter two species did not appear capable of extended coexistence.The size, the seasonal occurrcncc and life cycle, and the subgenus of each species are important factors that determine the type of congeneric association where Diaptomus spccics may coexist.
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