An integrated analysis of mammalophilic blackflies in the Simulium variegatum group in Laos

The simuliid fauna of Laos is among the most poorly known of any country in the world, only seven species having been recorded. We explored the Laotian simuliid fauna as an opportunity to test reproductive isolation and the minute morphological differences between two of the country's common isomorphic nominal species-Simulium chamlongi Takaoka & Suzuki (Diptera: Simuliidae) and Simulium luculentum Takaoka, Srisuka & Saeung (Diptera: Simuliidae). Both are members of the widespread Simulium variegatum group. Using the band patterns of the giant chromosomes in the larval silk glands, we showed that S. chamlongi and S. luculentum are reproductively isolated, no hybrids having been found. Molecular analyses indicated that the two species are genetically distinct, with a minimum genetic divergence of 2.91%. Analysis of a fragment of the vertebrate cytochrome b gene revealed that the blood hosts of S. chamlongi and S. luculentum in Laos include humans and water buffaloes (Bubalus bubalis Linnaeus) (Artiodactyla: Bovidae), respectively. Diagnostic morphological characters provided in the original species descriptions were substantiated for pupae and females but not for larvae or males. Our chromosomal analyses also revealed a third reproductively isolated species, possibly new, with a unique IIS chromosomal sequence. The absence of a uniquely shared inversion among the three species indicates that the S. variegatum group lacks a defining chromosomal synapomorphy.