Monsters vs. aliens: a natural history

April 2, 12:39 PMNY Gardening ExaminerMarc Montefusco

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Image courtesy Tina Carvalho ("Microangela")

In the interest of fairness, this article has nothing to do with the movie Monsters vs. Aliens, Paramount Pictures, 2009, currently in theaters, and which I almost certainly will never see (although Ginormica is kind of cute, in an oversized, Slavic way. I especially like the fact that she's one inch short of fifty feet tall – see Attack of the Fifty Foot Woman, Woolner Brothers Pictures, 1958). To be even fairer, a better title for this piece would have been Alien vs. Predator (20th Century Fox, 2004), but I like to stay au courant, so to speak, with popular culture. At this point, you're asking yourself, what is he talking about? The answer, of course, is aphids.

There are hundreds of species of aphids, and most of them are pests. Only a millimeter or so long, they can cause problems all out of proportion to their size. With the naked eye, they appear as tiny velvety lumps, but at higher magnifications, they appear completely alien and vaguely threatening. They are parthenogenetic, which means they can produce eggs without mating, which in turn means that they are incredibly prolific. A few aphids are a nuisance, a lot of aphids can injure or even kill a plant.

I had a lot of aphids on the hibiscus in my greenhouse this winter. They literally covered the buds, and blackened the leaves with "honeydew" – a euphemism for aphid excrement. I sprayed soap without any real effect, and oil not only failed to halt the invasion, but damaged the hibiscus flowers as well. I was contemplating more drastic means when I noticed something crawling on the window of the potting room. It was a ladybug, probably the Asian ladybug Harmonia axyridis, which has become something of a nuisance for householders, due to its habit of overwintering in buildings. I, on the other hand, was happy to see it. I carefully captured it and moved it into the greenhouse, where it promptly flew out through the ceiling vents. I closed the vents, found another, and dumped it onto a hibiscus leaf. It stayed put.

Over the next few weeks, I kept a sharp eye out for ladybugs, and transferred any that I found. I saw my first larva after about three weeks, and then began noticing orange egg clusters on the underside of the hibiscus leaves. Soon there were ladybug adults and larvae everywhere. The larvae share nothing with the cute adult form except coloring: they're long, lean, mean-looking eating machines, capable of devouring hundreds of aphids in their lifetimes. The adults eat aphids, too, but it’s the kids who are the real gluttons.

The aphid population took a decided hit. Soon several plants were entirely free of aphids, and it was then that I realized that ladybugs had had some help. Here and there I could see some beige aphid skeletons: empty aphid-shaped husks, with a neat hole cut out of the butt. I knew then that that the aphids had been attacked by parasitic wasps, genus Aphidius.

Whereas aphid larvae are simply voracious hunters, Aphidius wasps aren't just in it for the meat. These tiny wasps lay their eggs in aphids and other insects, where the egg hatches, and the larva devours the host insect from the inside out. At the appropriate moment, the wasp nibbles a neat round hole in the former aphid's abdomen, and climbs out to begin life as an adult wasp. (see John Hurt, Alien, Brandywine Productions, 1979). By the way, it was this kind of parasitism that led Darwin and others to question the idea of a benevolent creation, and indirectly contributed to the formulation of the idea of natural selection. At any rate, these wasps are a useful adjunct to ladybugs in controlling aphid populations, and now the hibiscus leaves look like little aphid graveyards, filled with the empty exoskeletons of departed aphids.

This was not the first experiment that I have conducted in biological warfare, but it was certainly an effective demonstration of the power of beneficial insects to control pest populations. All I did was transfer a few dozen ladybugs from one room to another – the wasps showed up on their own. Not all insect pests are as vulnerable as aphids, of course, and even the aphids will stage a resurgence. Like every horror movie ever made, just when you think the monster (or alien) is finally finished off, you see the claw or antenna or other appendage quiver just a little. Sequel, anyone?