Triatoma dimidiata is the vector of Trypanosoma cruzi in the Yucatan Peninsula (YP). Earlier studies have shown that domestic and peri-domestic populations of the vector originated from the sylvan stock and that effectiveness of insecticide-spraying was affected by re-infestations of houses from the sylvan T. dimidiata population. In addition, in the YP most previously published reports have focused on domestic and peri-domestic populations and very little is known about the nocturnal behavior of the sylvan populations. The main aim of our study was to determine the nightly activity patterns of adult T. dimidiata in a selected location in the YP. Secondly, we sought to document the reproductive status and infection rate of active females. During eight sampling nights spaced from late March to late July, 2007, we collected 544 adult T. dimidiata. We found that square-cloth illuminated white traps were effective to attract the sylvan individuals and that T. dimidiata adults exhibited a unimodal activity pattern throughout the night. The accumulated mean of captured bugs also showed a non-linear distribution for females and males. Furthermore, we found that male and female catches were significantly correlated with the means of temperature and humidity recorded during the sampling period. Out of 46 dissected females, we observed that 43.5% of females had fully-formed eggs in their abdomens, and only two females (4.4%) had sperm within the spermatheca. The infection rate of T. dimidiata harboring T. cruzi was found to be 3.7%. The implications of the light attraction to bugs and potential dispersal capabilities are discussed in the paper in the context of infestation/re-infestation of rural houses by sylvan T. dimidiata flying adults.