Oviposition preferences of Culex pipiens and Culex restuans for infusion-baited traps

The number of egg rafts oviposited by Culex pipiens and Culex restuans in infusion-baited ovitraps varied with the type of infusion substrate, infusion age, method of infusion preparation, and calendar date. In one or more tests, more Culex egg rafts were collected from water infused with Kentucky bluegrass sod, mixed grass clippings, straw, or a commercial rabbit chow than from a water control. Infusions prepared with oak leaves, maple leaves, and sod soil were ineffective as Culex oviposition attractants; however, alfalfa infusions ranged from marginally effective to unattractive. Rabbit chow infusions required one or more reinfusions before becoming active oviposition lures when prepared in unconditioned (unused) ovitraps. Infusions prepared in conditioned ovitraps (those that had previously contained the same type of infusion) had shorter delay periods. Effective oviposition lures for Culex species included continuous infusions, such as sod and sod grass, and those in which the substrate was infused in the water for only a brief period (24-48 h), such as infusions of rabbit chow and mixed grass clippings. The percentage of egg rafts from Cx. restuans was usually greater in sod and grass infusions than in rabbit chow infusions, whereas Cx. pipiens showed a slight preference for rabbit chow infusions over sod and grass infusions. The temporal shift in relative oviposition activity of the 2 Culex species (cross-over) varied from year to year and between sites in one year.