BIOASSAYS FOR CULEX (DIPTERA, CULICIDAE) MOSQUITO OVIPOSITION ATTRACTANTS AND STIMULANTS

Bioassay methods for mosquito oviposition attractants and stimulants w ere developed and compared, using Culex tarsalis Coq. gravid females a s test insects, and distilled mater, dyed water, or Bermuda grass infu sions as the test stimuli. Bioassays with sticky screens covering jars containing volatile test stimuli or with colorless and odorless Trito n X100 surfactant in the aqueous oviposition medium demonstrated that gravid mosquitoes were attracted to distilled water with the attractio n increased by the addition of dye, grass infusion, or the steam disti llate of grass infusion to the water. A variation of the sticky screen bioassay was used to demonstrate that the grass infusion also contain ed oviposition stimulants. A forced oviposition bioassay was minimally useful, because it failed to discriminate between a solution known to contain oviposition stimulants and a distilled-water control. Overall , the bioassays developed can be used to distinguish between ovipositi on attractants and stimulants, a distinction that cannot be made by si mply counting egg rafts.