Mealybug Invasion

long-tailed-mealybug-c-david-cappaert-michigan-state-university-bugwoodorg-2With temperatures dipping into the low 20s and our first (finally!) snowfall, the bugs in our gardens are either dead or in hiding. But before we collapse into that comfy recliner with a garden book and a cup of tea, we need to take a good look at our houseplants. It might be winter outside, but indoors the bugs are having a field day.

At least they are at our house. I’m currently at war with some aggressive invaders. They’re about an eighth of an inch long, are covered with sticky, gooey, white fluff, and are wedged into the leaf axils of many of my favorite houseplants. Yup, my indoor garden has mealybugs.

mealy-bugs-on-christmas-cactus-blkforest-2008oct14-lah-142At first glance, it looks like my plants have cotton all over them. Upon closer examination, you can see the segments of the dirty-gray or tan insects intent on sucking plant juices from the stems and leaves. (For some reason, they conjure up an image of a herd of minuscule sheep on a green pasture.) All that sucking disfigures the leaves, and can eventually overwhelm the plant.

Like their relatives the aphids, mealybugs produce honeydew—droplets of sugar syrup that make the leaves (and anything under them) sticky. In turn, sooty fungus feeds on the sugar, turning the leaves black. Besides looking pretty awful, the fungus can interfere with photosynthesis, further weakening the plant.

While neither I nor my plants are very happy about this situation, there is hope. Mealybugs are “unarmored scale insects” and are more easily controlled than their shelled kin. The hard part is exterminating them completely. I can get the upper hand, but I’ll probably be dealing with this pest for years to come.

mealybug-on-plumeria_lah_5658There are many different species of mealybug, but two are responsible for most houseplant damage: the citrus mealybug and the long-tailed mealybug. Both are most active in warm, dry weather—just what we have in our homes right now. The females lack wings, and must crawl from plant to plant. I’m always amazed they are able to get around our house so well, given that they can’t fly. The males are smaller and spend their days flying around looking for females to mate with. They resemble tiny gnats, and are easily overlooked.

Once mated, the females produce between 200 and 600 eggs. Long-tailed females retain the eggs in their bodies, and the young are born live. Citrus mealybug eggs are nestled into a waxy, cottony mass called an ovisac, where they are out of reach of most pesticides. So, rather than spraying, it’s much more effective to remove all the sticky fluff by hand, using a cotton swab dipped in rubbing alcohol. Of course, this can take some time and effort, especially if your plants are large or you have a lot of them.

There are other ways to combat mealybugs. You can try overwhelming force—by washing them off the plant with a strong stream of water. The kitchen faucet works well for small pots, while the shower suffices for larger plants.

You can try chemical warfare. Soap solutions are effective against mealybugs, but you must make sure the spray drenches the insect. Various brands are available, or you can simply mix a tablespoon of liquid dish detergent with a quart of water.

Using more toxic sprays on houseplants isn’t a good idea if you have children or pets who might come in contact with the leaves. If you want to use an insecticide, look for one containing permethrin, pyrethrin, resmethrin, or azadirachtin. (Please note that while all these are naturally occuring chemicals, they are still poisons and should be handled with caution.)

The best results will come from a combined attack. I usually wash the plant, then carefully remove all the insects I can see. I finish up with a soap spray. A week or two later, I repeat the whole process, since new eggs will likely have hatched. Vigilance is key.

Finally, if you can’t seem to beat the bugs, it’s probably best to discard the plant and start over. Make sure you inspect any newcomers before buying them, and quarantine them for a week or two before adding them to your indoor jungle. As with most things, prevention is far easier than a cure.

For more information, check out Colorado State University’s Plant Talk #1466: Mealy bugs on houseplants.

Top photo of a long-tailed mealybug by David Cappaert, Michigan State University, Bugwood.org

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