Orange sulphur

Description

Colias eurytheme, the orange sulphur, also known as the alfalfa butterfly and in its larval stage as the alfalfa caterpillar, is a butterfly of the family Pieridae, where it belongs to the lowland group of "clouded yellows and sulphurs" subfamily Coliadinae. It is found throughout North America from southern Canada to Mexico. Other members of this lineage including the common or clouded sulphur (C. philodice) and C. eriphyle and C. vitabunda, which are often included in C. philodice as subspecies. Hybridization runs rampant between these, making phylogenetic analyses exclusively utilizing one type of data (especially mtDNA sequences) unreliable. Therefore, little more can be said about its relationships, except that it is perhaps closer to C. (p.) eriphyle than generally assumed, strengthening the view that the latter should be considered a valid species. The orange sulphur's caterpillars feed off various species in the pea family (Fabaceae) and are usually only found feeding at night. Occasionally this species multiplies to high numbers, and can become a serious pest to alfalfa (Medicago sativa) crops. The parasitoid wasp, Cotesia medicaginis can be used as a biocontrol agent against the caterpillars. C. eurytheme butterflies can be found from southern Mexico to almost all throughout North America. Historically, they were distributed primarily in the western Nearctic, but were displaced to the east by logging and alfalfa field planting. Studies have suggested that most of the genes controlling male courtship signals are inherited as a co-adapted gene complex on the X-chromosome. The X-chromosome carries most of the genes controlling production of 13-methyl heptacosane, the main component of pheromones involved in sexual selection, and the ultraviolet wing reflectance pattern. Expression of the ultraviolet wing reflectance pattern found in male C. eurytheme is controlled by a recessive allele on the X-chromosome. This trait is sex limited and not expressed in females of the same species. Unlike that of many other butterfly species, the courtship of C. eurytheme is very brief and does not involve many elaborate displays. Mature female butterflies participate in mate selection by utilizing a specific refusal posture that prevents any undesired mating with both conspecific and non-conspecific males.