Aphids are everywhere. You'll find these tiny insects clustered on both the rose bush outside your window and the houseplant inside it. Aphids have soft bodies – no outer shell – and few defenses other than sheer numbers along with an undiscriminating appetite for trees, shrubs, perennials, annuals, and vegetables. If it grows, there's an aphid that will eat it.
Why such a varied palate? Because everything eats aphids; they are the mice of the insect world. They are a favorite meal of ladybugs, syrphid fly larvae, lacewings, minute pirate bugs, earwigs and even birds, to name just a few. That means, like mice, they must be prolific reproducers.
There are over 4000 species of aphids on the planet. They come in a rainbow of colors: green, white, black, red, gray, orange, even pink. Woolly aphids are white and fluffy. Common names for aphids include plant lice, greenfly and blackfly.
Aphids usually hang out on the undersides of leaves, or on plant stems. Since they have piercing-sucking mouthparts, aphids enjoy a liquid diet; they don't chew, like beetles and caterpillars. They suck the juices out of plants. The more succulent a plant, the more irresistible. The softest, most tender parts of a plant are where the new growth is (or as it is called in horticulture-speak, the terminal growth), so the tips of a plant are where you'll find them.
Bad infestations can turn leaves yellow, make them curl, or wilt. Aphids can disfigure a plant, but with the exception of seedlings, will rarely kill one that's healthy and established. However they will disfigure a flower bud or fruit by feeding on it.
Aphids can also carry viruses on their mouthparts, which can infect plants. Their honeydew attracts other insects and funguses such as sooty mold. These are more damaging, so large amounts of aphid activity on a plant shouldn't be ignored.
On a scale of damage from none to a plague of locusts, aphids rate as a nuisance more than a threat, which is why it's rarely necessary to use chemical controls. They are one of the easiest insects to remove from a plant: handpicking, blasts of water, ladybugs and other benign controls usually do the trick. Create a welcoming garden environment that encourages beneficial insects, and aphid damage will be minimal.
Some fun facts about aphids:
Aphids are generally wingless and stationary, but periodically a generation is born with wings, enabling them to fly (or, more accurately, drift on wind currents) from a depleted host plant to others with better nutritional prospects.
Since aphids suck the sap – which is essentially sugar – from plants, their excrement is sugar-loaded as well. Known as honeydew, it's a delicacy for certain types of ants, which will "farm" aphids by protecting them from predators, moving them around a plant, and even bringing some back to the nest to overwinter.
Aphids have this neat trick to keep multiplying, especially when predator numbers are high: they reproduce by parthenogenesis. Put another way, females can reproduce without males. These offspring are all female, and they can't reproduce this way indefinitely. Males are essential for genetic diversity.
Some of the few plants that are turn offs to aphids are garlic, chives, marigolds, dill, and catnip.
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