Aphids reproduce asexual

Parthenogenesis, or asexual reproduction, is the first key to an aphid's long family tree. With few exceptions, aphids in spring and summer are all females. The first wingless matriarchs hatch from eggs in early spring, equipped to reproduce without the need for male mates. Within a few weeks, these females produce more females, and soon after that, the third generation arrives. And so on, and so on, and so on. The aphid population expands exponentially without the benefit of a single male.

http://insects.about.com/od/truebugs/p/aphidsreproduce.htm