OVIPOSITION BEHAVIOR OF NATURAL-POPULATIONS OF CULEX-TARSALIS AND CULEX-RESTUANS (DIPTERA, CULICIDAE) IN ARTIFICIAL POOLS

Natural populations of Culex restuans Theobald and Cx. tarsalis Coquillett in Manitoba, Canada, preferred to oviposit in artificial pools (ovipools) where lawn sod used as an attractant was renewed regularly during the season. The sod medium was unattractive to most Cx. restuans after three weeks in the spring, after one week in midsummer, and after two weeks in autumn; it was unattractive to most Cx. tarsalis after three weeks. Cx. restuans was the first Culex spp. to oviposit each spring, and in 1986 overwintered females of Cx. restuans began ovipositing four weeks before those of Cx. tarsalis. Both species continued to oviposit until September between 1984 and 1987 or until the mean weekly air temperatures dropped to 12 degrees C. Cx. restuans selected shaded oviposition pools, located under a tall, dense tree canopy, while Cx. tarsalis selected open-field, unshaded pools. CO2-baited light trap collections of adults near the oviposition site showed that Cx. restuans females were underrepresented in comparison with the number of egg rafts collected.