CHEMICAL CUES AND WATER QUALITY SHAPE MOSQUITO OVIPOSITION DECISIONS: EVIDENCE FROM FOUR FIELD-RELEVANT TREATMENTS

Mosquito oviposition site selection is governed by chemical, physical, microbial, conspecific, and heterospecific cues, which can alter water composition and breeding site quality, yet field-based evaluations of how specific water chemistry parameters influence egg-laying behavior remain limited. Improving the sensitivity of oviposition-based surveillance tools, such as ovitraps, requires identifying chemical cues that reliably attract or deter gravid females under field conditions. We assessed oviposition responses of wild mosquito populations, including Aedes aegypti and Ae. albopictus, to 4 water treatments (geosmin-beetroot peel extract [hereafter geosmin extract], pH, salinity, and sucrose) across a gradient of concentrations at 4 field sites in Indian River County, FL, from September to December 2025. Egg counts were collected weekly from paired ovitraps and analyzed using negative binomial generalized linear mixed models with Dunnett's post-hoc contrasts and oviposition activity indices (OAI). Geosmin extract at the highest dose (3.75 ml) significantly increased oviposition by 123% relative to controls (P < 0.001), making it the only stimulant identified. Salinity produced a strong dose-dependent deterrent effect, with complete oviposition cessation at 3% (OAI = -0.56, P = 0.003). Sucrose showed a consistent deterrent trend, with evidence of significant reduction at the highest concentration. pH modifications showed variable but generally deterrent effects, with pH 9.0 reducing egg counts by 55%. These findings demonstrate that geosmin extract is a promising field-deployable stimulant for improving ovitrap sensitivity in surveillance programs, whereas salinity and sucrose function as effective oviposition deterrents. Notably, this study provides the first field evidence that a crude aqueous extract prepared from red beet (Beta vulgaris) peels, a natural source of geosmin, stimulates oviposition by gravid Ae. albopictus, extending previous work conducted exclusively on Ae. aegypti.