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GARDENING : Puny, Prolific Aphid Brings Gardeners to Their Knees

January 12, 1991|CLARK SHARON | SPECIAL TO THE TIMES

It was bound to happen--invasion.

You scan the terrain and there they are, aphididae of the order Homoptera, clinging to your favorite rosebushes and doing the two things they do best--eating and birthing babies. This has got to stop, you say, as your roses seemingly shrivel before your eyes. Stoically you gird yourself for battle. Chemical munitions are brought up to the front. The enemy is engaged.

After 10 minutes of fierce hand-to-tarsi combat, the rout is total. The invading hordes are swept from the field, not to mention the petals and stems of your sagging roses. You bask in the triumph of humankind over one of the bug world's most notorious pests. Your roses are saved. Victory is sweet. Then, two weeks later. . . .

Theeeyyy'rrreee bbbaaaccckkk!!!

Behold the mighty aphid. Like a zombie on the lam, you never know just where or when it will show up. You are only certain that it will.

Puny, prolific to boot, with a life cycle as complex and shifting as a teen-ager's social calendar, the aphid as a species survives massacre and murder thanks to an indestructible law of nature--nothing can kill aphids as fast as they can reproduce.

For this reason there isn't a garden or field on earth--let alone in Orange County--that doesn't have at least a few aphids hanging around it from time to time. And where there are a few aphids, if left unchecked, there will soon be a lot of aphids.

Remembering that this is a family newspaper, it can be said that aphids are among the most sexually prodigious of creatures. The birds and the bees may do it, even educated fleas may do it, but Cole Porter would have been amazed at the way aphids do it.

The female aphid is an expert at parthenogenesis--the act of single-gender conception. Using this form of reproduction there is no need for a male aphid or the ardors of insect passion; no moonlit trysts among the jasmine, no coy intermingling of antennae, no mating rituals to slow things down.

Virgin live birth is actually a chromosomal cloning of the mother aphid. New offspring are female duplicates of dear old Mom. In a sense, they are dear old Mom. As if this wasn't enough, females are born pregnant, a neat trick called paedogenesis. The resulting generational scramble means that daughter aphids are not only sisters to their mothers, they are mothers themselves, and their mothers are grandmothers even before their own pregnant daughters--who are their sisters--are born.

If that confuses you, think what it does to the male aphid who is a straightforward type only looking for some way to sabotage all this solo reproduction. He will get his chance, but only during those times of year when the female aphid shifts biological gears from live birth to egg-laying.

Cold and storm can wipe aphids out by the zillions, but not so the weather-resistant black eggs they leave in the protected nooks of tree branches.

With that certain nip in the air, male aphids do their masculine duty by helping to trigger egg-laying in the females. This not only assures survival of the colony during the harsh winter months, it stirs the gene pool by later hatching out male and female aphids of mixed heritage.

Over time there has been a lot of gene stirring going on because aphids today flourish in some 4,000 known species around the globe. Nick Nisson, an entomologist for the Orange County Agricultural Center in Anaheim, says about 120 different kinds of aphids have been identified so far locally--and every one of them reproduces like crazy.

Let's crunch some numbers.

Say a single female aphid gives birth to an average of 100 pregnant offspring, and that each of these pregnant offspring in turn gives birth to yet more pregnant offspring, and factor in up to 40 birth cycles a year per aphid . . . let's see, X multiplied by Y, added to Z, carry the four . . . well, it's a lot of aphids. British aphidologist A.F.G. Dixon calculates about 600 billion in just nine generations--or as little as seven weeks.

So why isn't the earth, given such mathematical possibilities, covered with a crust of aphids 3 feet thick? Probably because aphids are good to eat. To other bugs, that is.

Given half a chance, any number of bugs will gladly munch an aphid. In fact, the aphid is the Big Mac of the insect world. Billions are served daily.

The ladybird beetle (or ladybug, of nursery rhyme fame) is a voracious predator of aphids. A single ladybug can devastate an entire aphid colony in a matter of days, if not hours. Its culinary gusto is both spectacular and disgusting. Amplified recordings of ladybug feeding frenzies are as delicate as an ax murder in progress.

Parasitic wasps are among the more gruesomely inventive of the aphid predators. Planted by a parent as larva inside a living aphid's body, these tiny wasps slowly consume their host from the inside out.

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