Phlebotomine sand flies are biological vectors of Leishmaniosis worldwide. Given the development of insecticide resistance and impact on non-target species, ecofriendly and sustainable surveillance and control methods over sand fly populations are required. One such approach targets gravid females by using oviposition-site attractants as bait. Most work in this field has focused on olfactory cues but very little is known about the role of visual cues. To study this issue, we used Phlebotomus papatasi, a vector of old-world Zoonotic Cutaneous Leishmaniasis (ZCL), as a model system. P. papatasi is a nocturnal/crepuscular sand fly that typically breeds in animal burrows. Therefore, we hypothesized that gravid females would be attracted visually to objects resembling a burrow opening. Specifically, we tested if gravid female sand flies are attracted to round black cups (resembling burrow opening) compared with clear or white cups (control) and how does illumination level, gender, and stage affect such preference. We also evaluated if visual cues alter gravid female responses to a known olfactory attractant. Finally, we tested if sand flies lay more eggs on black or white surface.
Results/Conclusions:
Generally, gravid females were significantly attracted to black cups compared to white or clear cups. However, their attraction differed with illumination level. At dim light they preferred black cups over white and clear. At reduced (red) light they preferred black cups only over clear cups, and at complete dark they have no preference. In addition, the preference for black cups was specific only to gravid females but was not exhibited by young females and young or mature males. In contrast with the above, oviposition response was not affected by substrate color. Finally, our results indicate that olfactory cues might be influenced by visual cues. Specifically, we found that attraction to a known olfactory cue source (larval growth medium) differed with respect to cup color and illumination level. Black cups especially distracted gravid females from the olfactory cue. Our work provided additional evidence of the role of visual cues for oviposition site selection and might have some practical implications for oviposition trap design as well as for optimizing experimental design of future research studying sand fly oviposition behavior.