Pemphigus (genus)
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Pemphigus Hartig, 1839 - (petiolegall aphids)
This genus of aphids contains around 70 species which are found in the northern hemisphere. The sexual stage forms galls on polar leaves, usually the petioles. The asexual stage (if present) can be found on the roots of a variety of plants, including crops like lettuce, cabbage or beet. The main damage is caused on the secondary hosts. Both stages differ considerably morphologically and often include special soldier casts on the primary host which defend the galls from predators.
The winged adults are about 2 mm long, dark and covered with wax. In a common scenario, the females lay their eggs in autumn on the bark of poplar trees and these hatch in spring. A nymph emerging from an egg induces the poplar leaf to form a gall which encloses the developing nymph. Once mature the aphid produces a second generation inside the gall and the offspring develops into winged adults. The gall then opens and the winged adults migrate to the secondary summer host where the females lay egg around the roots. The asexual summer form might go through several generations on the roots. At the end of the summer, winged males and females fly off to poplars and mate. Typically each female then lays only one large egg on the poplar host.
Type species: Pemphigus bursarius
Currently, the following species have been entered into the system:
