Mealybugs cause damage to several crops in the horticultural sector. The most important species occurring in the glasshouse belong to the genera Planococcus and Pseudococcus. Within the Planococcus genus, the citrus mealybug Planococcus citri is a particular problem; several species within the Pseudococcus genus occur in glasshouses.

Life Cycle

The mealybug has five stages in its life cycle. The females go through the stages of egg, three nymphal stages and adult insect; the males go through egg, two nymphal stages, false pupa and adult insect. Mealybugs derive their name from the third larval stage onwards when the female's body is covered with a white wax-like substance in the form of powder, filaments, projections or plates.

Damage symptoms

• Nymphs and female adults feed on plant sap. This reduces growth, and causes deformation and/or yellowing of the leaf; sometimes leaves even drop off the plant. This can reduce yield or cause cosmetic damage. Infested plants often drop flowers or leaves if present.
• Mealybugs excrete honeydew, on which dark soothy moulds develops. Together with the whitewax-like secretions these soil the plants. Photosynthesis of the leaves reduces, causing the production to decrease.

Mealybug Control

Description: Found in warmer growing climates, mealybugs are soft-bodied wingless insects that often appear as white cottony masses on the leaves, twigs, or fruit of plants. They feed by inserting long sucking mouthparts, called stylets, into plants and drawing sap out of the tissue. Damage is not often significant at low pest levels. However, at higher numbers they can cause leaf yellowing and curling as the plant weakens. Feeding is usually accompanied by honeydew, which makes the plant sticky and encourages the growth of sooty moulds. Mealybugs are a common greenhouse pest that affect ornamentals, houseplants, avocados, and fruits.

Adults (1/10 - 1/4 inch long) are soft, oval distinctly segmented insects that are usually covered with a white or gray mealy wax. Small nymphs, called crawlers, are light yellow and free of wax. They are active early on, but move little once a suitable feeding site is found.

Note: There are approximately 275 species of mealybugs known to occur throughout the United States.

Life Cycle: Adult females deposit 300-600 eggs within their compact, cottony mass. Egg laying is continues for about 2 weeks with the female dying shortly after all eggs are laid. Hatching occurs within 1-3 weeks and the small active yellow nymphs begin migrating over the plant in search of feeding sites on which to settle. As they feed, they secrete honeydew and a waxy coating begins to form over their bodies. Female nymphs pass through three stages (instars) with a generation taking as little as one month, depending on temperature. Male nymphs pass through five instars. They do not feed after the first two instars and exist solely to fertilize the females. In the greenhouse, continuous and overlapping generations occur throughout the year. There is little winter survival outside of greenhouses in the North.

Mealybug Control: Prune out light infestations or dab insects with a Q-tip dipped in rubbing alcohol. Do not over water or overfertilize - mealybugs are attracted to plants with high nitrogen levels and soft growth. Commercially available beneficial insects, such as ladybugs, lacewing and the Mealybug Destroyer (Cryptolaemus montrouzieri), are important natural predators of this pest. Use the Bug Blaster or hose off plants with a strong stream of water to reduce pest numbers. Washing foliage regularly will help discourage future infestations. Insecticidal soap contains potassium salts of fatty acids, which penetrates and damages the outer shells of soft-bodied insect pests, causing dehydration and death within hours. If pest levels become intolerable, spot treat with botanical insecticides.

Tip: Control ants when releasing beneficial insects. Ants feed on the honeydew that mealybugs produce and protect them from predators to ensure this food supply.

Identify mealybugs by looking on the undersides of leaves and around leaf joints. These insects look like small (1/10 to 1/8 of an inch) balls of cotton. Mealybug-damaged plants look withered and sickly and may have sticky sap on the leaves and stems.

Step 2Spray a strong jet of water directly on to the affected area of the plant. The stream washes the insects off. This is the easiest way to control mealybugs.

Step 3Spray with a soap/oil mixture if the water alone doesn't do the job. Mix 1 tsp. insecticidal soap, 1/2 tsp. horticultural oil, and 1 quart water in a spray bottle. There are also numerous chemical products available for the control of mealybugs.

Step 4Use rubbing alcohol and a cotton swab to treat minor infestations. Dab the rubbing alcohol directly onto the insects.

Step 5Try purchasing and releasing a natural predator called mealybug destroyer (Cryptolaemus montrouzieri) for serious infestations. Place the mealybug destroyers directly on the infested plant.

Step 6On an ongoing basis, attract other types of predatory insects, such as parasitic wasps (Leptomastix dactylopii), that will consume and control mealybugs. Grow their favorite plants such as dill, fennel, coreopsis and brightly colored flowers near the mealybug-prone plants.

Step 7Select and plant plants that are naturally resistant to mealybugs. These include plants with a milky sap and thick or fuzzy leaves - they'll vary depending on where you live

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

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.