Visual cues modulate oviposition behavior in laboratory-reared gravid black flies Simulium vittatum Zetterstedt (Diptera: Simuliidae)

Color vision in hematophagous insects is a core sensory mechanism that enhances the detection of contrast during host seeking, oviposition site, and substrate selection. Understanding the effects of visual cues on black fly oviposition behavior can be a useful tool for control in field settings. This study evaluated the modulatory role that substrate color plays in oviposition behavior of laboratory-reared Simulium vittatum (Zetterstedt) (Diptera: Simuliidae) gravid females. We conducted multi-choice oviposition assays to examine the effects of color treatment (white, yellow, green, and grey egg sheets) on oviposition behavior and egg-laying densities. Results revealed a highly significant effect of color treatment on egg deposition (F3, 15 = 33.58, p < 0.001, η2 = 0.898), which explained 89.80% of the total variance in egg distribution. White egg sheets resulted in significantly higher egg percentages (50.75 ± 7.33%) compared to yellow (18.20 ± 2.47%), green (15.95 ± 2.52%), and grey (15.07 ± 5.58%), representing a 2.5-fold difference between white and grey options. These results highlight the importance of visual cues in shaping oviposition behavior in S. vittatum and offer actionable insights for optimizing egg collection efficiency as a control measure under field settings. These findings can be further explored to enhance the design of gravid traps, decoy substrates or push-pull tools for black fly control.