Aphids thrive by the sheer force of their numbers. Their secret: Because just about every insect predator looks at them as an appetizer, their only chance of survival is to outnumber them. If aphids are good at one thing, it's reproducing.
Consider this fact from entomologist Stephen A. Marshall in his book "Insects: Their Natural History and Diversity": In optimal environmental conditions and lacking any predators, parasites, or disease, a single aphid could produce 600 billion descendants in one season. Just how do these tiny sap suckers multiply so prolifically? They can change the way they reproduce and how they develop as environmental conditions change.
Aphids Can Reproduce Without Mating (No Males Needed!)
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 (from eggs laid late the prior year to overwinter), 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 a single male.
Aphids Save Time by Giving Birth to Live Young
The life cycle goes much quicker if you skip a step. Aphid mothers are viviparous, meaning they give birth to live young during the spring and summer, rather than laying eggs during these seasons. Their offspring reach reproductive maturity much sooner since they don't have to sit around waiting to hatch. Later in the season the females and males both develop.
Aphids Don't Develop Wings Unless They Need Them
Most or all of an aphid's life is spent feeding on a host plant. It doesn't need to go very far, so walking suffices. Producing wings is a protein-intensive task, so aphids wisely conserve their resources and their energy and remain wingless. The aphids do quite well in their apterous state until food resources run low or the host plant gets so crowded with aphids that the group must disperse. Only then do they need to grow some wings.
When the Going Gets Tough, the Aphids Get Going
High populations, which occur quickly in light of the aphids' prolific reproduction, lead to less than optimal conditions for survival. When there are too many aphids on a host plant, they begin competing with each other for food. Host plants covered in aphids are rapidly depleted of their sap, and the aphids must move on. Hormones trigger the production of winged aphids, which can then take flight and establish new populations.
Aphids Adapt Their Life Cycle to Environmental Conditions
All would be for naught if the aphids in cold climates just froze to death at year's end. As days become shorter and temperatures fall, aphids begin producing winged females and males. They find suitable mates, and the females lay eggs on perennial host plants. The eggs will carry on the family line, producing next year's first batch of wingless females.