This ugly little creature is the larva of the leaf-eating ladybird. Stressed plants in prolonged hot, dry conditions attract these pests. The larvae become almost black as they reach pupa stage. Both adults and larvae of leaf-eating ladybirds are particularly fond of the Solanum family (tomato, potato, eggplant) and the melon or squash family where they do a lot of damage to leaves.
The adult leaf-eating ladybird has 26 or 28 spots in rows across its wing covers. They are slow moving and drop to the ground when disturbed. In summer, if you see the adults on leaves in your garden, be sure to look under the leaves for their eggs. Remove small leaves containing eggs and, on large leaves, use a knife to scrape the eggs into a container. As I dislike spraying my garden, I just squash the adults and larva with a gloved hand.
Unfortunately, the damage done by these ladybirds and their offspring have resulted in many gardeners spraying other species of ladybirds that are voracious pest predators. Both adults and larvae consume a considerable quantity of pests such as aphids, scale and mites, and one type of ladybird feeds on fungus. Peter Chew and his family have an excellent website, Brisbane Insects and Spiders, where gardeners can easily identify which creatures are beneficial to their gardens and which are pests, and includes a Ladybird Field Guide.
The photo below shows both larva and pupa stages of the 28-spotted ladybird.
These sap-sucking pests are can be found on the twigs and branches of a range of plants, including fruit trees. The pests themselves may not attract much attention unless the plant is heavily infested because they are reddish-brown in colour with black hairs, and only 5 mm in length. The part we notice as a pest is actually the scale’s egg sac – a grooved, white, wax structure, larger than the insect itself. The egg sac will contain up to hundreds of red eggs. (See photos below).
Before treating these pests – check that you haven’t confused them with the larvae of the mealy bug ladybird, which are also white and fluffy. Ladybirds and their larvae consume an enormous amount of scale insects and aphids, but many of the larvae are killed when they are confused with pests. Many pest predators are killed where copper sprays are routinely used, and scale infestations commonly follow spraying for other pests.
When the cottonycushion scale prepares to lay her eggs, she fixes herself to the twig. Give the white structure a poke, if it doesn’t move, it’s scale – ladybird larvae will scuttle off. When temperatures are below 24° C, and pest predators are absent, cottonycushion scale can be suffocated by spraying with white oil at 10 ml per litre of water. This will not kill the eggs, and the spray will have to be repeated in two weeks, to catch the newly hatched scale.
In warmer weather, suffocate spray with enough fine potter’s clay dissolved in water to make it cloudy. Pest infestation is a sign that plants need an improved fertiliser and/or watering program, or that you need to adjust your soil pH.