In hot, dry weather the 26 or 28-spotted ladybirds can do a lot of damage to the vegetable patch. Plants can only absorb nutrients from the soil as water-soluble ions. As soil dries out, vegetable plants are unable to absorb the nutrients they need to produce the compounds that deter pests, and these troublesome ladybirds can move in, feeding on leaves until only a network of veins remain. The larvae (pictured below) tend to feed on the underside of leaves while the adults feed on the upper sides of leaves. Badly damaged eaves can become papery, and brown. Their favourite foods are the cucurbit or squash family, which includes the melons. They can also attack, bean, potato and tomato plants.
The problem with using sprays to get rid of these pests is that whatever will kill them will also kill the beneficial ladybirds that help keep many garden pests under control, including the bright black and yellow ladybird that eats powdery mildew and other fungi. Fungus-eating ladybirds are often seen wandering over leaves of the squash family.
The Brisbane Insects website now has a field guide to ladybirds to make it very easy for you to identify whether the tiny creatures crawling on your plants are pests or ladybird larvae, which come in a range of colours and shapes.
Click here: Ladybird Field Guide
The best way to solve the problem of 26 (or 28)-spotted ladybirds is to knock the adults and their larvae into a soup tin with some methylated spirits in the bottom of it. Also scrape off the eggs, which can be found in a cluster on the underside of leaves (see photo below).
Then give the foliage and soil around the plants a generous drink of seaweed extract tea, to supply potassium and trace elements plants need to build resistance to pests, because only stressed plants are attractive to pests. Ensure the plants have sufficient fertiliser for healthy growth, and that the soil is not too acidic or too alkaline. Water the plants thoroughly, under mulch, when the top cm. of soil is dry, rather than giving them a lighter, daily watering. If drought conditions are making it difficult to spare enough water, you can help deter them by spraying both sides of the leaves with chilli spray, but you will need a lot of chillis. The solution is – 2 cups chillis to 2 cups of water. Chop chillis finely while wearing gloves. Steep them in water for an hour, strain mixture, and spray liquid over leaves. (Garlic spray can be used as a deterrent but breaks down quickly in hot weather.) Finally, get rid of any blackberry nightshade plants. These act as a host for this little pest. See:Blackberry Nightshade
Eggs and larvae of the 26 (or 28)-spotted ladybird.