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.
- Univoltine - (adjective) referring to organisms having one brood or generation per year
- Bivoltine - (adjective) referring to organisms having two broods or generations per year
- Multivoltine - (adjective) referring to organisms having more than two broods or generations per year
- Semivoltine - (adjective) referring to organisms whose generation time is more than one year
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.
The number of breeding cycles in a year is under genetic control in many species and they are evolved in response to the environment. Many phytophagous species that are dependent on seasonal plant resources are univoltine. Some such species have the ability to diapause for a large part of the year, typically during a cold winter. Others that bore in wood or other low-grade, but plentiful, food material may spend nearly the entire year feeding, with only brief pupal, adult and egg stages to complete a univoltine life cycle. Yet other species that live in tropical regions with little seasonality may be highly multivoltine, with several generations feeding on constantly growing vegetation (such as some species of Saturniidae or continually renewed detritus, such as Drosophila and many other genera of flies with a life cycle of just a week or two.
- Aalberg Haugen IM, Berger D, and Gotthard K. 2012. The evolution of alternative developmental pathways: footprints of selection on life-history traits in a butterfly. 12pp. Journal of Evolutionary Biology, 25:7, Available online: 
- Coates BS, Sumerford DV, and Hellmich RL. 2004. Geographic and voltinism differentiation among North American Ostrinia nubilalis (European corn borer) mitochondrial cytochrome c oxidase haplotypes. 9pp. Journal of Insect Science, 4:35, Available online: 
- Hunter, M.D. and J.N. McNeil. 1997 Host-plant quality influences diapause and voltinism in a polyphagous insect herbivore. Ecology 78: 977-986. 
- Timothy Duane Schowalter (2011). Insect Ecology: An Ecosystem Approach. Academic Press. p. 159. ISBN 978-0-12-381351-0.
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