Within the Hemiptera, the Sternorrhyncha form the largest and most complex group. Within the Sternorrhyncha, the same applies for the Aphidomorpha, the aphids and relatives. Aphidomorpha have an exceedingly long proboscis (that may be retracted within the when not in use).
Many Aphidomorpha species demonstrate hostplant alternation. A fertilised female then deposits her eggs on plant species A; the progeny develops there but, once full grown migrates to plant species B, where a number of parthenogenetic generations follow. Against the end of the season along with females also males are formed, and the cycle restarts. Plant species A, the primary hostplant, generally is a tree or shrub, B, the secondary one, a herb. Some species have again simplified the cycle: they live, either faculatatively or entirely, parthenogenetically on the secondary host plant.
Aphididae form the largest group of the Aphidomorpha. They are characterised by having a pair of dorsal, generally tubular glands wehere honeydew is excreted: the siphunculi ( = siphons = cornicles). The aphids on the secondary host plants are viviparous.
Blackman & Eastop (2014), Börner & Heinze (1957a), Holman (2009a), Richards & Davies (1977a).