Oviposition circadian rhythms of sand flies, vectors of Leishmaniases, are poorly understood. We sought to determine when gravid females are most responsive to oviposition-site attractants (temporal attraction) and when they deposit their eggs (temporal oviposition). We hypothesized that sand flies would be most responsive to oviposition site cues during the night with peak attraction preceding peak oviposition. Flies were kept in a climate controlled room (27C and 80% RH) with the light phase between 18:00-5:00 and dark phase between 6:00-17:00. Crepuscular conditions occurred at 17:00-18:00 and 5:00-6:00. For temporal attraction, a cup containing an attractant (larval frass) with a sticky, metal mesh on top, was placed inside a 12”x12”x12” cage containing 20 gravid females. The mesh was removed and replaced at three-hour intervals and the flies caught were counted (N=24). For temporal preference, a similar design was used with two cups (one with larval frass, one with sand) placed into the cage (N=24) and flies chose between them over three hours (times: 18-21, 0-3, 3-6, and 9-12). For temporal oviposition, a cup with larval frass with a moist filter paper was placed into a cage with 20 gravid females that oviposited over a three-hour period, then the eggs were counted.
Results/Conclusions
Our results indicate that peak attraction occurs during the last three hours of the night and peak oviposition occurs during the first three hours of the night. This suggests that gravid females are more attentive to oviposition cues during the last three hours of the night. This observation is consistent with field-observations showing flies tending to enter rodent burrows during the latter part of the night. Based on these results, we suggest that gravid flies seek for suitable oviposition site during the late part of the night but that they actually oviposit early in the following night. In addition to enhancing our understanding of the biology of oviposition circadian rhythm, these results are also useful by informing subsequent studies in terms of timing of oviposition attraction and stimulation bioassays.