Where mosquito larvae are found is not just a function of where their predators are not. Female mosquitoes selectively choose habitats to promote survivorship of their offspring. To better understand the habitat choices of the southern house mosquito, STPMAD has performed egg-laying choice experiments with 5-gallon buckets. By counting egg rafts deposited overnight in various manipulations of water type, we’ve confirmed that these mosquitoes cannot distinguish buckets with larvicide products that will kill their offspring compared to water without those products. We’ve also confirmed that these mosquitoes prefer water that is heavily polluted with sewage from unmaintained or not properly functioning OWTS. Diluting water from these treatment systems results in at least six-fold fewer egg rafts and replicates the effect of rain diluting pollutants.
In a separate study during the summer of 2021, STPMAD Taxonomist Lisa Rowley setup an egg laying choice experiment using a continuum of sewage strength and mosquitofish water (fish chemical cues only) (see figure above). No egg rafts were deposited in 100% mosquitofish water. Four-fold more eggs (119 in total) were laid in water collected from a polluted ditch than in any other treatment. Why mosquitoes prefer to oviposit in sewage-polluted water remains unknown and could be due to the lack of fish presence, presence of chemical cues from other mosquitoes, or due to the quality of nutrients in this habitat. Future manipulations of these choice experiments may shed light on why female southern house mosquitoes bet their offspring on and in sewage-polluted habitats.