Photoperiodism and life cycle plasticity of an aphid, Macrosiphum euphorbiae (Thomas), from central North America

Photoperiodic responses are described for five clones of the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae), from Manitoba, Canada, a region with a strongly seasonal, continental climate. When exposed to long nights, parthenogenetic wingless females produce winged males and parthenogenetic winged females that subsequently produce mating females. The young adult males and winged females are restless and take flight readily, which is typical of a post-teneral migratory phase that-could carry them to 1 winter host. These traits are characteristic of host-alternating species. However, wingless females also produce mating females, and winged females also produce parthenogenetic wingless females, traits which are characteristic of nonhost-alternating species. Clones differ in the frequencies of phenotypes they produce, some being more host-alternating than others. Critical night lengths are shortest and frequencies of males highest for clones that are closest to the host-alternating type of life cycle. The importance of phenotypic and genotypic plasticity in the life cycle is discussed.