Mealybugs are a small insect that is common outdoors and in greenhouses. It often gets into homes through plants bought from nurseries or the garden trade. They are a form of unarmored scale insects.
Mealybugs damage plants by sucking their juices, weakening them and often spreading fungus and diseases. Plants will become less vigorous and will eventually, if untreated, die. Mealybugs love to settle in the crotches where leaf petioles join the stem.
They attach themselves to the plant and secrete a powdery wax layer (hence the name "mealy" bug) used for protection while they feed.
Mealybug damage is less obvious than many other pests. Leaves will brown, growth will slow and the plant will show signs of weakness and sickness. Visual identification is easiest, the cottony bodies of mealybugs are easy to see upon close inspection.
Unlike other pests like spider mites, mealybugs rarely kill a plant outright unless left to completely get out of hand. But the damage is unsightly and should be treated to keep your ornamental plants looking their best.
Mealybugs lay up to 600 small, yellow eggs in a protective cottony mass.
Egg-laying is dependent on temperature - fewer eggs are laid at high temperatures and humidities. Some species of mealybugs don’t lay eggs, but bear live young in a manner similar to aphids. After laying eggs over a period of five to ten days, the female dies. Young female mealybugs go through three stages of development. Newly hatched mealybug nymphs (called crawlers) are yellow to orangish or pink, lack wax, and are quite mobile, but they begin to excrete a waxy covering soon after settling down to feed. Immature males (nymphs) settle and spin a white, waxy cocoon. Adult males are tiny and winged, but rarely seen, and only live a few days.
One generation develops every one to three months depending on temperature.
Mealybugs can be treated fairly well and with patience can be eradicated. Populations can be controlled through a few different stratgies to minimise any damage to a collection.
Always quarantine new plants away from your collection for at least two weeks, and thoroughly inspect the plant for damage and pests both in the shop before purchase after getting it home and before moving it into a room with other plants. Look for the white fluffy mealybugs and for other pests like spider mites, thrips or scale.
After inspection, rinse the foliage of the plant with firm blasts of water to dislodge any hidden insects or eggs.
A horticultural oil, such a Neem or Peppermint oil can be used to control some stages of mealybugs. It can be bought in solution or mixed in a 1:100 ratio to water with some dish soap to break down the oil so it mixes with the water.
Important: Some plants are sensitive to oils and to soap - so google the plant first or try the solution on a small part of a leaf, wait 24 hours and check for discolouration or browning.
Spray the plant thoroughly. Oils work on contact with mealybugs or their eggs or larvae. Get it into all crotches and folds in the plant. Leave for 10 minutes and then rinse the plant down with water.
It's important to repeat this every 3 days for two weeks to effectively control mealybugs.
Horticultural oils should be used in tandem with rubbing alcohol.
Use a cotton bud or piece of fabric dipped in alcohol (rubbing alcohol, isopropyl alcohol, surgical spirits or neat vodka) and dab the cottony surface of any mealybugs on the plant. Be careful to work in stages to not miss any hiding mealybugs.
Repeat this every few days, knocking off the dead mealybugs as you go until you no longer see any evidence of pests on the plant.
Dinotefuran or imidacloprid are insecticides that is effective in the control of mealybugs. However availability varies between countries and is a controlled substance in many others. Always follow the directions on the container.
Releasing beneficial insects into a collection serves two purposes - firstly they often attack stages of the pest that are hard to see with human eyes such as the pupal or larvae stages of pests. They also work around the clock and with bad infestations can rapidly reduce pest numbers.
Ladybird adults or larvae are natural predators of mealybugs and other soft bodied pests such as whitefly eggs, aphids, scale insect and young caterpillars. The Australian ladybird Cryptolaemus montrouzieri is a voracious killer of mealybugs.