A strain of Anopheles albimanus Wiedemann with white pigmentation on the dorsum of the thorax in larvae and pupae was selected. Genetic crosses were made with this mutant marker, White thorax (stw), which showed it to be part of an allelic series with Stripe (st+) and Non-stripe (st). The st+ character is completely dominant over stw, and st is recessive to both st+ and stw.