Introgressive hybridization, also called as introgression, is the gene flow from one species to another when the mating occurs between species. Usually, the introgression plays a major role in evolution, but it is still contested. We aim to understand the introgression and its frequency using a probabilistic approach. The proposed method involves Bayesian inference of gene trees, reconciliation of gene trees and the species tree, and phylogenetic hypothesis testing over evolutionary phylogenetic networks. We apply our method to investigate the extensive introgression events using genomic data of 16 anopheline mosquito species from Africa, Asia, Europe and Latin Africa spanning over 100 million years of revolution.