Understanding the biological parameters of some triatomine subspecies of Meccus phyllosomus (Burmeister) is a crucial first step in estimating the epidemiologic importance of this group.Biological parameters related to hatching,lifetime,number of blood meals to molt,percentage of females at the end of the cycle,number of laid eggs,and mortality for each instar of 3 M.phyllosomus subspecies [M.p.mazzottii (Usinger),M.p.pallidipennis (St(a)l),and M.p.phyllosomus] and their laboratory hybrids were evaluated and compared.No significant differences (P ＞ 0.05) were found among the experimental hybrids (MaPa,MaPhy,PaPhy) and reciprocal cohorts.In 5 (hatching,number of blood meals to molt,accumulative mortality,percentage of females,and mean number of laid eggs) of the 6 studied parameters (with the exception of development time),the hybrid cohorts had better fitness results than the parental cohorts involved in each set of crosses.The increase in hybrid fitness found in our study could lead to an increase in the epidemiologic risks caused by transmission of Trypanosoma cruzi to humans.