Mealy bugs are soft, plump, cottony-looking insects with piercing/sucking mouth parts. They exude a dense covering of water-repellent waxy filaments that acts as a protective device. Mealy bugs favour dry conditions.
They prefer to feed under cover, so they tend to congregate in leaf axils, leaf sheaths, the underside of leaves, and in crevices. They congregate in colonies where they suck the sap from the soft young shoots, leaves and stems, robbing plants of essential nutrients. Prolonged attacks may weaken and even kill plants.
Mealy bugs only tend to be serious pests in the presence of ants because the ants protect them from predators and parasites.
In her book ‘What Garden Pest or Disease is That?’ Judy McMaugh says:
‘Mealybugs and mites tend to be worse on plants that are sprayed regularly for other pests. The sprays that kill the pests also kill the ladybirds and lacewings etc, which usually attack mealybugs and mites and keep their numbers under control. However, ants (some of which actually 'farm' mealybugs and aphids) should be controlled by spot spraying.’
Many gardeners think that low toxicity sprays containing pyrethrums are less damaging to the environment than very toxic sprays like Rogor. That is not really the case. While it is true that the low toxicity sprays break down very quickly, they are efficient at killing all insects, including their predators. As the sprays that break down quickly need to be used more frequently than the more toxic systemic sprays, use of pyrethrums and similar sprays means that you are also spraying the predators more frequently. The Botanic Gardens has suggested that the systemic sprays (eg Rogor) could be used as a ‘pour in’ treatment rather than be sprayed on to the foliage of plants. ‘Pouring’ should minimise damage to the predator insects.
Eliminating Mealy Bugs
The first rule is to inspect your plants regularly to catch them early. It’s far easier to kill one or two bugs than to eradicate a full-blown infestation.
The Water Cure
In the early stages, blasting the bugs off with a strong stream of water works well. This should be repeated on a daily basis until the mealy bugs are gone.
For larger infestations, use equal parts of dishwashing liquid and water – stir to mix rather than shaking to avoid excess foam. Spray all infected areas. The soap coats the mealy bugs and suffocates them. It also breaks down their protective waxy layer. Rub the leaves with a soft cloth after spraying to remove the bugs, or leave the solution overnight and then attack the weakened bugs with a strong jet of water.
Spot treat areas of mealy bug infestation with a cotton ball soaked in rubbing alcohol – simply dab the insects and rub them away.
A large range of predators attacks mealybugs. Small birds such as hornbills, silver-eyes and pardalotes feed avidly on them, as do hunting spiders, parasitic wasps, ladybird beetles and their larvae, and the larvae of hoverflies and lacewings.