Aphids Give Birth to Live Clones

Aphid female giving parthenogenetic birth

Why are there always seemingly innumerable aphids on plants? How come roses in a garden never have just one or two, but are covered in these little bugs, especially near the growing tips where the young tissue is easily pierced by the aphids' mouthparts to feed? The answer lies in the very plants they feed on: the aphid life-cycle and morphology is tailored to take direct advantage of available food sources. This is evident is in an impressive array of adaptations, on of the most startling being that species can reproduce asexually through parthenogenesis.
While female morphs predominate, male are produced in the autumn (1). Mating occurs to produce eggs that overwinter, hatching to produce females that give parthenogenetic birth to live young, which in turn reproduce parthenogenetically. This can result in huge numbers, which explains their ability to seemingly overwhelm plants if left uncontrolled. The young that are produced may be winged or wingless, with the winged individuals dispersing while the wingless are more optimised for reproduction. Such adaptations have been described by John Sorensen as nutrition driven evolution. Aphid life strategy means the individual is expendable but guarantees the survival of their genes.

References:

1. Sorensen, 2009. In Encyclopedia of Insects pp. 27-31