Voltinism

Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism.

Examples

The speckled wood butterfly is univoltine in the northern part of its range, e.g. northern Scandinavia. Adults emerge in late spring, mate, and die shortly after laying eggs; their offspring will grow until pupation, enter diapause in anticipation of the winter, and emerge as adults the following year - thus resulting in a single generation of butterflies per year. In southern Scandinavia, the same species is bivoltine - here, the offspring of spring-emerging adults will develop directly into adults during the summer, mate, and die. Their offspring in turn constitute a second generation, which is the generation that will enter winter diapause and emerge as adults (and mate) in the spring of the following year. This results in a pattern of one short-lived generation (ca. 2 months) that breeds during the summer, and one long-lived generation (ca. 10 months) that diapauses through the winter and breeds in the spring. An example would be the bee species Perdita portalis. Perdita portalis is bivoltine and is estimated to have about 2 or 3 broods annually. During winter, larvae remain in diapause, in their pharate or prepupal adult stage. This diapause stage continues until metamorphoses is complete in the next spring or summer and the bees emerge as adults.