Mealybug Control in Your Garden

Mealybugs are sometimes difficult insects to control because of their habit of feeding in secluded parts of plants. The first thing you might notice is Sooty Mould building up. Keep an eye out (see Monitor) for Sooty Mould while you are watering your plants. If you find sooty mould, then you should see if you can find what caused it.

Regular monitoring of your plants either indoors or out in the garden, will ensure that a major infestation of Mealybugs doesn’t occur ‘overnight’. Managing Mealybugs is much easier if you can catch an infestation in its early stages. Don’t wait for an infestation to build up to unmanageable levels.

Prevention is always better than cure. The only way Mealybugs can get into your garden or your house is on a plant. Check plants and cuttings for Mealybugs before bringing them into your garden or into your house. 

There are several things that you can do to prevent or minimise Mealybug damage (see How to Prevent Mealybugs Appearing). The trick is to not let them build up in such high numbers that they are causing major damage (see Symptoms of Mealybugs).

To treat Mealybugs on indoor and outdoor ornamental plants, as well as vegetables like Broccoli, Brussels sprouts, Cabbage, Cauliflower, Beans, Peas and Tomatoes, use Yates Baythroid with Yates Advanced Garden Insect Killer. For large infestations, use Yates Nature’s Way Vegie & Herb Spray Concentrate. Mix in a sprayer and spray all surfaces of the plant thoroughly, repeating every 5-7 days if required. These are contact sprays, so ensure you cover the plants and pests thoroughly, including on the undersides of leaves.

Mealybugs (Pseudoccidae) are sap sucking insects related to Scale Insects. More than 200 species of Mealybugs occur in Australia, many of which are native, but there are several introduced species as well. Pest species encountered in gardens are more likely to be introduced than native.

Common pest species include Citrus Mealybug (Planococcus citri), Citrophilous Mealybug (Pseudococcus calciolariae), Hibiscus Mealybug (Maconellicoccus hirsutus), Longtailed Mealybug (Pseudococcus longispinus) and Tuber Mealybug (Pseudococcus viburni). Of these Mealybugs, Citrophilous Mealybug is native, and the others are introduced.

Female Mealybugs are usually oval in shape and less than 5 mm in length. They secrete a powdery (‘mealy’) waxy substance which covers their bodies, and some species have filaments of wax extending around their bodies. Some species may have very long filaments extending from the rear.

Eggs are usually laid in a sticky mass of waxy threads known as an ‘egg sac’, and eggs may be pale yellow or orange, depending on the species.

Nymphs are initially yellow-brown in colour and not covered with wax, and are known as ‘crawlers’. Female nymphs develop their waxy covering at the second nymph stage.

Adult males are seldom-seen, tiny, winged insects which don’t feed and are about 1 mm long.

Female Mealybugs of some species (e.g., Longtailed Mealybug) lay live young (i.e., ‘crawlers’) under their bodies, but most species lay eggs into a waxy egg sac. Adult females lay 300 to 600 eggs over a period of 1 to 2 weeks.

Nymphs hatch and, if they are destined to become females, pass through three nymphal instars before adulthood.

Male Mealybugs have four nymphal stages. Males only feed in their first and second instars and then pass through two non-feeding instars. The last two stages are completed inside a waxy cocoon that is produced by the second-instar nymph. Adult males only live for a few days. Their only role in life is to find females and mate with them.

The full life cycle takes from 6 to 12 weeks depending on the species, and there may be several generations per year.

Adult females and nymphs tend to feed in sheltered parts of plants such as between fruits and leaves that are touching, inside leaf sheaths, the base of stems, and sometimes the roots.

• Fruits – especially citrus, Figs and Grapes.
• Many ornamental plants including Cactus, Fuchsia, Gardenia, Hibiscus, Jasmine and Oleander.
• Many houseplants including Coleus, Ferns, Ficus, Orchids, Palms and Philodendron.
• Greenhouse plants are particularly prone to Mealybug attack, because the warm, humid environment is ideal for Mealybugs.

• Look out for Sooty Mould developing. The presence of Sooty Mould is an excellent indicator of sap sucking insect activity.

• Don’t bring them in. Check plants and cuttings for Mealybugs before bringing them into your garden or house.
• Prune dense foliage to minimise sheltered feeding spots.
• Honeydew attracts Ants, which protect the Mealybugs from predators and parasites in return for a feed of honeydew. Prevent Ants climbing trees by banding trunks with horticultural glue.
• Mealybugs may breed in weeds. Control weeds.
• Prune heavily infested foliage and dispose of it.

• Several species of native parasitic wasps (see Beneficial Wasps).
• Naturally occurring Lacewings and Ladybird species.
• The Native Ladybird Beetle, Cryptolaemus montrouzieri, is a commercially available Mealybug predator. This beetle has been exported to other countries where it is known as ‘Mealybug Destroyer’.