Q. What is worse than biting into an apple and finding a worm?
A. Finding half a worm.
The “worms” in apples are usually caterpillars of the coddling moth, Cydia pomonella, (although a number of other insect species also tunnel into apples). Coddling moths lay their eggs on apples. The caterpillar hatches and chews a hole through the peel and tunnels into the interior. The entrance hole opens the apple to infection by pathogens, causing the fruit to rot. This prevents apples from being sold for fresh market (partly rotten) or from surviving in storage.The availability of effective pesticides led apple growers to spray their trees to control coddling moth. The pesticide would not penetrate the apple and kill larvae that had burrowed into apples, But the pesticide would coat the outer peel of the apple. As caterpillars hatched, they would contact pesticide as they crawled on the surface and consuming the peel would deliver a lethal dose of pesticide to kill the caterpillar. For a short time, the apple growers succeeded in protecting the apples.
However, coddling moth caterpillars soon became resistant to pesticide treatments through a simple behavioral change. Instead of eating the apple peel, the pesticide resistant coddling moth caterpillars would spit out the peel as they chewed their way into the interior of the apple. Thus, they avoided consuming the pesticide and did not die. Once in the apple interior, caterpillars are out of reach of the pesticide. Insects frequently develop resistance to control measures. Thus entomologists are always busy trying to find new and better ways of controlling insect pests.