Prodigal Summer - Barbara Kingsolver [121]
“They are over here. I can keep them under control my own way, normally. But your spraying always causes a caterpillar boom.”
He shook his head. “How many times do I have to listen to that nonsense?”
She leaned forward, her eyes growing wide. “Until you’ve heard it!”
“I’ve heard it. Too many times.”
“No, now, I haven’t explained it to you right. I always had a hunch, but I couldn’t put it in words. And, see, last month they had a piece on it in the Orchardman’s Journal. It’s a whole scientific thing, a principle. Do you want me to get you the magazine, or just explain it in my own words?”
“I don’t think I have any choice,” he said. “I’ll listen for the flaw in your reasoning. Then you’ll have to hush up about this for good.”
“Good,” she said, shifting her bottom on the basket. “All right, now. Goodness, I feel a little bit nervous. Like I’m back in college, taking an exam.” The anxious way she looked up at him reminded Garnett of all the years of boys who’d feared him in his vo-ag classes. He wasn’t a mean teacher; he’d just insisted that they get things right. Yet they’d dreaded him for it. They were never his chums, as they were with Con Ricketts in shop, for instance. It made for a long, lonely life, this business of getting things right.
“OK, here we go,” she said finally, clasping her hands together. “There are two main kinds of bugs, your plant eaters and your bug eaters.”
“That’s right,” he said patiently. “Aphids, Japanese beetles, and caterpillars all eat plants. To name just a few. Ladybugs eat other small bugs.”
“Ladybugs do,” she agreed. “Also spiders, hornets, cicada killers, and a bunch of other wasps, plus your sawflies and parasitic hymenoptera, and lots more. So out in your field you have predators and herbivores. You with me so far?”
He waved a hand in the air. “I taught vocational agriculture for half as long as you’ve been alive. You have to get up early in the morning to surprise an old man like me.” Although, truth to tell, Garnett had never heard of parasitic hymenoptera.
“Well, all right. Your herbivores have certain characteristics.”
“They eat plants.”
“Yes. You’d call them pests. And they reproduce fast.”
“Don’t I know it!” Garnett declared.
“Predator bugs don’t reproduce so fast, as a rule. But see, that works out right in nature because one predator eats a world of pest bugs in its life. The plant eaters have to go faster just to hold their ground. They’re in balance with each other. So far, so good?”
Garnett nodded. He found himself listening more carefully than he’d expected.
“All right. When you spray a field with a broad-spectrum insecticide like Sevin, you kill the pest bugs and the predator bugs, bang. If the predators and prey are balanced out to start with, and they both get knocked back the same amount, then the pests that survive will increase after the spraying, fast, because most of their enemies have just disappeared. And the predators will decrease because they’ve lost most of their food supply. So in the lag between sprayings, you end up boosting the numbers of the bugs you don’t want and wiping out the ones you need. And every time you spray, it gets worse.”
“And then?” Garnett asked, concentrating on this.
She looked at him. “And that’s it, I’m done. The Volterra principle.”
Garnett felt hoodwinked. How could she do this every time? In another day and age they’d have burned her for a witch. “I didn’t find the fault in your thinking,” he admitted.
“Because it’s not there!” she cried. “Because I’m right!” The little woman was practically crowing.
“The agricultural chemical industry would be surprised to hear your theory.”
“Oh, fiddle, they know all about it. They just hope you don’t. The more money you spend on that stuff, the more you need. It’s like getting hooked on hooch.”
“Pssht,” he scolded. “Let’s don’t get carried away.”
She leaned