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Aphids

08/20/02 12:00AM By Ruth Page
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(Host) Every gardener knows aphids - but here's Ruth Page with facts about how some aphids can nest a couple of future generations of clones inside her while she seeks a home.

(Page) There are about 4,000 species of aphids in the world. Why doesn't that surprise me? These tiny characters come in an assortment of colors and live off the sap in our plants. Every gardener knows them. They're often called "ant cows" because ants, which love the "honeydew" aphids secrete, protect them. Luckily, ladybird beetles consume aphids by the thousands - real gardeners' helpers.

Now along comes Science News to tell us that a few species of aphids can form colonies, somewhat as bees and ants do, and exert - even sacrifice - themselves, for the good of the group. Self-immolating aphids - how about that? Each such colony is founded by a super-productive female whose daughters, as teenagers, grow Schwarzenegger-type legs that help them defend the colony from predators such as lacewing larvae. A larva is a lot bigger than an aphid, but can be killed by sheer numbers of heavy-legged aphids. All aphids have strong sucking mouthparts, too, to slurp the sap from a plants. The mouthparts can also pierce an intruder's body, sometimes fatally. In some colonies, the teenage soldier aphids never grow up, but spend their entire lives as protecting the colony.

As for sex, most aphids can take it or leave it. They indulge in sexual reproduction occasionally, but often several generations are produced asexually, so all mom's young are her identical clones. Such species have a tremendous secret for rapid reproduction. In a species in the American West, a female who has mated lays all-female eggs under cottonwood tree-bark. When these young specks hatch, each crawls under loose bark until she discovers a leaf-bud, where she stays to suck sap. The leaf forms a gall - a wall-like growth around her - that will be her home henceforth.

Here's the stunner: embryonic clones of that mom were developing inside her while she did her home-search. Inside each of those, another batch of clones has started growing. They're nested, like those wooden Russian dolls.

When you're no bigger than a pinpoint, you need sheer numbers to have any effect, so these aphids can cause a population explosion without sex. The first clones to emerge are soldiers who spend the summer protecting the gall for the other clones. These soldiers then grow wings and fly off. They alight on mustard-family plants, spread along the roots, and give birth to the daughters waiting within them. By winter, the latest generation moves to a cottonwood tree. This group produces a few sons along with a few daughters. They mate; females lay eggs, and the whole cycle starts again in spring.

This is Ruth Page, impressed by the life cycle of one of a plant-grower's constant annoyances.
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