Explaining how and why reproductive isolation evolves and determining which forms of reproductive isolation have the largest impact on the process of population divergence are major goals in the study of speciation. By studying recent adaptive radiations in incompletely isolated taxa, it is possible to identify barriers involved at early divergence before other confounding barriers emerge after speciation is complete. Sibling species of the Anopheles gambiae complex offer opportunities to provide insights into speciation mechanisms. Here we studied patterns of reproductive isolation among three taxa, An. coluzzii, An. gambiae s.s. and An. arabiensis, to compare its strength at different spatial scales, to dissect the relative contribution of pre- versus post-mating isolation, and to infer the involvement of ecological divergence on hybridization. Because F1 hybrids are viable, fertile, and not uncommon, understanding the dynamics of hybridization in this trio of major malaria vectors has important implications for how adaptations arise and spread across the group, and in planning studies of the safety and efficacy of gene drive as a means of malaria control. We first performed a systematic review and meta-analysis of published surveys reporting on hybrid prevalence, showing strong reproductive isolation at a continental scale despite geographically restricted exceptions. Second, we exploited our own extensive field datasets collected at a regional scale in two contrasting environmental settings, in order to assess: i) levels of pre-mating isolation; ii) spatio/temporal and frequency-dependent dynamics of hybridization, iii) relationship between reproductive isolation and ecological divergence, and iv) hybrid viability penalty. Results are in accordance with ecological speciation theory predicting a positive association between the strength of reproductive isolation and degree ecological divergence, and indicate that post-mating isolation does contribute to reproductive isolation among these species. Specifically, only post-mating isolation was positively associated with ecological divergence, whereas pre-mating isolation was correlated with phylogenetic distance.