Development time and fitness: is there an adaptive development delay in the Rhodnius prolixus fifth nymphal stage?

Triatomines (Hemiptera: Reduviidae) are vectors of Trypanosoma cruzi Chagas, the etiological agent of Chagas's disease. They display pre-adult development delay - that is, a development time much longer than on average - which usually has been considered as a maladaptive trait. However, this hypothesis has not been tested. We carried out an experiment under controlled laboratory conditions to (1) test whether a development delay exists in the fifth nymphal stage of Rhodnius prolixus Stal (Hemiptera: Reduviidae, Rhodniini), and (2) measure any fitness cost related to such delay by estimating the relationship between individual development time and other life-history traits. We analyzed the development time with various continuous statistical distributions (normal, log-normal, Weibull, gamma, Pareto, Burr, and log-logistic). Using goodness-of-fit tests, the best fit was obtained with asymmetrical distributions, with the Burr distribution showing the best fit to the data. We concluded that a development delay exists in stage five of R. prolixus without fitness cost. The combination of our results and previous work suggests that such a delay could be viewed as an adaptive response to environmental stochasticity and/or density-dependence rather than as a maladaptive trait. We propose further investigations to provide a conclusive test of adaptive delay in triatomines.