The diurnal flights of Reticulitermes spp. have been reported to occur in the spring and early fall in northern California. From the spring of 1994 until the fall of 2001, we collected hundreds of alates of Reticulitermes spp. cuticular hydrocarbon phenotypes CA-A/A′ and CA-D during flights from multiple locations in the San Francisco Bay Area. As predicted, there were two flight seasons: one in the spring from February to May and one in the fall from October to December. The flights in the spring were made only by phenotypes CA-A/A′; those in the fall exclusively included phenotype CA-D. These disparate flight times indicate that reproductive isolation is complete and provide further biological evidence that phenotypes CA-A and CA-A′ are variants of one taxon and are distinct from CA-D.