Where do fruit flies, aphids come from?

DEAR JESSICA: I gave a friend a cactus plant years ago. It grew to be a big, beautiful plant, then out of nowhere came the aphids. He said he couldn't care less about destroying or throwing out the plant. I feel badly because I watched this plant flourish over the years. I don't want to bring it inside my house out of concern for my plants. What do you suggest? And where do these pests come from in the first place? -- Joan Grahn, Smithtown

DEAR JOAN: Let's get the easy question out of the way: Aphids, also called plant lice, are tiny parasitical insects with piercing-sucking mouthparts, which they attach to soft plant parts and suck the life out of them. They often can be dealt with easily by rinsing plants with a nice blast of water from the hose or sink sprayer, essentially knocking them off. If you do this, take care not to drench the soil; this is a cactus, after all.

Sometimes, depending on the plant and the level of infestation, and because aphids reproduce so rapidly, this might not be effective. Insecticidal soap, widely available at garden centers in concentrate form, is a good Plan B. Follow package directions. On the off chance the aphids remain, there are systemic insecticides available as a last resort. If you resort to them, look for a product labeled for use against aphids and follow package directions carefully (do not overapply or you may harm the plant).

Where do aphids come from? Where do fruit flies even come from? These mysteries elude most people. It just doesn't seem reasonable that they would appear out of thin air without parents, but they do, don't they?

Interestingly enough, and contrary to popular opinion, fruit flies don't just appear out of nowhere. They have a super-strong fruit-seeking instinct that senses ripening fruit. As long as there are a couple of fruit flies outside your house, they will find a way in and zero in on those bananas on your counter, where they settle in, lay eggs and reproduce like crazy. Sometimes they've already laid eggs on fruit in the grocery store, so you get a bonus with your fruit purchase. Regardless, those eggs turn into full-fledged adults ready to breed in just a week.

It seems odd that houseplants would contract pests that don't normally reside in the house, but they do. If the cactus has vacationed outdoors for the summer, then that's where the aphids found it. But if it was indoors when it became infested, there can be other explanations. Did your friend repot the cactus? Sometimes bagged potting mix contains eggs or insects that attack your plant when you settle them into what you think is a clean new home.

And you're right to be concerned about your other plants. It's possible to buy an infested plant without realizing it, so if a new plant was brought into the house, aphids might have hitched a ride and later spread to the cactus.

Ditto if your friend keeps cut garden flowers around in vases. And if there are ants in the house, it's possible they brought the aphids to the buffet: Ants enjoy the sweet sticky honeydew excreted by aphids after ingesting plant matter, so they often carry aphids to plants and wait around for their treats.

DEAR JESSICA: Some of the mum plants in the garden bend when they get watered, as if the flowers become too heavy for the stalks. Sometimes part of the plants become upright again while other parts do not and hang over. Also, and somewhat related, some of the plants, without being watered, are not clustered but have become separated. One can look straight down into the plant and see an opening as if there were separate plants planted close together. I do not remember if they were clustered before they bloomed and, having been watered, separated permanently. In both instances, how can I avoid the problem and restore the plants to a cluster? -- Gerard Andreaccio, Valley Stream

DEAR GERARD: An opening in the center of a plant is a sure sign it needs to be divided. I'm guessing the plant has been in your garden for several years and has become overgrown. To resolve this for next year, you'll need to dig up the plant when it's dormant in March, before it comes out of dormancy. Insert a spade or long-handled garden fork in sections all around the plant, leaning on and rocking the tool's handle with each segmentation to loosen the root ball. Lift the plant out and, using a flat-edged spade, cut the root system into two or more pieces, depending upon the size of the plant. If the plant is small, you can gently tear the root apart by hand.

To improve the upright habit of Chrysanthemums and encourage them to grow stockier, trim the top third off the entire plant when new growth is 8 inches tall, typically at the beginning of June. Repeat two weeks later, and again two weeks after that. Don't worry about removing buds; the plant will produce more and, in fact, bloom more heavily in the fall.