Why Are There So Many Aphids?

Mass of aphids.
Aphids reproduce at a startling pace. Paul Starosta/Getty Images

Aphids thrive by the force of their numbers. When just about every insect predator looks at you as an appetizer, your only chance of survival is to outnumber them. If aphids are good at one thing, it's reproducing.

Consider this factoid from entomologist Stephen A. Marshall: 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 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, 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, rather than laying eggs. Her offspring reach reproductive maturity much sooner since they don't have to sit around waiting to hatch.

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.

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. Once there are too many aphids on a host plant, the aphids begin competing with each other for food. Host plants covered in aphids are rapidly depleted of their sap, and the aphids must move on. Now's the time to grow some wings. Hormones trigger the production of winged aphids, which can then take flight and establish new populations. If everyone's got enough food and elbow room, more will survive.

Aphids Adapt Their Life Cycle to Environmental Conditions

In some circumstances, aphids gain an advantage by switching to more traditional means of reproduction. 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 tree, producing next year's first batch of wingless females.

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Hadley, Debbie. "Why Are There So Many Aphids?" ThoughtCo, Apr. 11, 2017, thoughtco.com/why-are-there-so-many-aphids-1968631. Hadley, Debbie. (2017, April 11). Why Are There So Many Aphids? Retrieved from https://www.thoughtco.com/why-are-there-so-many-aphids-1968631 Hadley, Debbie. "Why Are There So Many Aphids?" ThoughtCo. https://www.thoughtco.com/why-are-there-so-many-aphids-1968631 (accessed January 21, 2018).