Mealybugs: a pest insect we should all learn to dread on our plants! Their populations can creep up on you and be difficult to control. This is why it’s important to treat plants once you find this pest.

Longtail mealybugs

Longtail mealybug are easy to identify from their threadlike tails.

Photo Credit: ©2005 Buglady Consulting

Immature mealy bugs

Immature mealybugs hang out on the stem of a plant.

Photo Credit: ©2003 Buglady Consulting

What do mealybugs look like?

Commonly found on houseplants, these small insects are 1-4 millimeters long. The females are covered with a white, cottony or mealy wax secretion and look like tiny cotton balls on plants, taking away a plant’s aesthetic value. They’ve got an oval body outline, and functional legs allow them to be mobile in their immature stage. Some mealybugs are more ornate than others, having filaments around the edge of their bodies or even “tails.” Immature males and females look similar, but they’re very different as adults: The adult male looks like a gnat with one pair of wings. (Only the adult males fly.) Female crawlers go though four developmental stages until they reach maturity. The male goes through five.

Adult female mealybugs can lay up to 600 eggs, usually found in a cottonylike sac beneath her body. (One exception is the longtail mealybug, which gives live birth to crawlers.) On average, within six to 14 days, the eggs start to hatch, and immature scale crawlers emerge. This stage varies with plant species and indoor temperature. When it does occur, it’s the time when dispersal to new plant parts or new plant hosts occurs. So in other words: This is when you want to target treatment!

What kind of damage do mealybugs do?

Once the crawler selects a feeding site, it inserts its mouthpart (called a stylet) and begins feeding on plant sap. While eating, a sticky waste substance is excreted by the insect (commonly called honeydew). This liquid adheres to leaves and provides a medium for sooty mold to colonize and grow. Sooty mold is black and eventually covers leaves and stems. This mold inhibits infected portions of the plant from photosynthesizing and causes aesthetic damage.

In addition to the sooty mold, plant damage is caused by the mealybugs sucking plant sap and the pests’ toxic saliva, both resulting in distorted plant growth and premature leaf drop. Plant leaves also develop yellow chlorotic spots.

How do you control mealybugs?

It’s important to always inspect any plant before you bring it home. Not doing so is how most people get pest problems. If mealybugs do find their way to your plants, there are a few control methods you can try.

Yellow sticky cards can be used to trap the flying adult males, preventing them from mating. (These cards can be purchased online.)

Insecticidal soaps and horticultural oils work great in controlling this pest. The tricky part is mealybugs tend to hide very well where leaves attach to the stem, so make sure you get coverage there. Horticultural soaps and oils don’t have systemic properties, which means when spraying, the product must come in contact with the pest. So know where your pest is on the plant.

A word of warning: You can burn leaves with horticultural soaps and oils. These products need to be applied when the air temperature is cool. Make sure your plants were watered well the day before you apply your control – never spray wilted plants. Following labeled rates also reduces the risk of leaf damage. More is not better. Also, make sure beneficial insects are not present when you spray. (Insecticides can kill the good guys, too.)

There are a few beneficial insects that can help you with mealybug treatment, too. Green lacewings (Chrysoperla sp.) feed on the crawler stage of almost any mealybug, where some others are more specialized – like the mealybug destroyer (Cryptolaemus montrouzieri). This beneficial insect is a type of ladybug that loves to feed on most mealybug species (although it doesn’t do well on the longtail mealybug). There is also a parasite specific to the citrus mealybug that’s commercially available. All these are available through the Internet.

Mealybugs can be controlled if you catch them early and time your treatment correctly. Crawlers are the easiest to kill, so time your spray right, and you can win the war against mealybugs.