A range of caterpillar pests cause problems in home gardens (as well as food crops). Here are the top 7 caterpillar pests in Australia…
Pest managers are often asked by homeowners to deal with pest problems on their ornamental, vegetable or fruit plants. Often the plants are under attack from a caterpillar pest. But identifying the specific caterpillar pest can be a bit tricky. Identification of the pest is often narrowed down by the type of plant attacked and the nature of the damage. Spotting their corresponding adults flying around may indicate that there’s a problem or a problem may develop in the near future. But as many caterpillar pests belong to moths, which are nocturnal, it is not always easy to spot the adults for identification. Correct identification is important as it provides an understanding of the behaviour of the pest at hand, in particular its feeding habits, which impacts the recommended control measures.
Cabbage white butterfly
Whilst most caterpillars belong to moths, there is one significant butterfly pest: the cabbage white butterfly (Pieris rapae). Introduced by accident from England or Europe, it was first spotted in Melbourne in 1929. It has now spread across much of the eastern seaboard, from southeast Queensland around to Adelaide, across Tasmania and in southwestern Western Australia. It has even been recorded in far north Queensland and central Australia. As its name suggests, it is a particular pest of brassicas, such as cabbages, cauliflowers, brussels sprouts, turnips and radishes. Their velvety green caterpillars, which can grow up to 30 mm in length, can defoliate plants, especially in higher numbers. They tend to be more of a problem in the warmer months, dying off during winter. Two species of parasitic wasp were introduced in the 1940s to help control numbers and appear to have helped. In the home garden, physical removal and the use of netting is a viable option. For sprays, Bacillus thuringiensis israelensis (Bti) products offer a targeted and effective solution.


Diamond back moth
Diamond back moth (Plutella xylostella) is also a pest of brassicas, although its caterpillar has very different feeding habits and is more difficult to control. The young caterpillars burrow into the leaves to feed before moving to the exterior of the leaf to feed on the underside as they get older. The small caterpillars cause ‘pinholing’ damage, but as the caterpillars develop, ‘windowing’ damage becomes prevalent.
There is a high level of resistance to insecticides in the diamond back moth, particularly to pyrethroids, but resistance is even appearing with some of the newer chemistries. Spraying should only be considered as a last resort when numbers are high. Bti sprays continue to be a good option, as although it may take a day or two to kill the caterpillar, the product won’t impact the adult stages of the beneficial insects. As the crop develops, the caterpillars may get into the brassica heads, which protect them from insecticide sprays.


Looper caterpillars
A number of moth species belonging to the Geometridae and Noctuidae families produce ‘looper’ caterpillars (also known as inchworms). As their name suggests, these caterpillars demonstrate the classic cartoon caterpillar movement. The caterpillars of some species can grow quite large – over 50 mm. They are often well camouflaged against the plants on which they feed, often mimicking twigs. They tend to be active at night, which is why you can wake in the morning to suddenly notice significant damage to a plant. In the home garden situation, physical removal of the caterpillars and the use of netting will often provide the best results.

Cluster caterpillar
The cluster caterpillar or tropical armyworm, Spodoptera litura, gets its name from the feeding habits of the young caterpillars – they feed as a group, destroying the leaf from underneath. Apart from this feeding habit, it can be distinguished from the fall armyworm in that it has two lines of black dots or triangles along the back. The caterpillars start off as a light green translucent colour and get darker as they get older. The adults are a combination of grey, brown and cream patches and wavy lines. They are also called cotton leafworm for the problems they cause in cotton, and tobacco cutworm, due to their annoying habit of cutting off seedlings at their base. However, they are known to attack over 500 types of crops, trees and weeds. Physical removal in the home garden is generally the best course of action.

Light brown apple moth
The light brown apple moth (Epiphyas postvittana) is native to Australia and although it attacks a wide range of plants, it is a particular problem on apple, pear and citrus trees. The young caterpillars are pale yellow-green but darken as they age. The caterpillars will cause damage to both foliage and fruit. Damaged fruit will still develop with surface scars, although in severe infestations there can be some fruit drop. They will typically hide in silk webbing and rolled up leaves to feed. As an identifying feature, the caterpillars vigorously wriggle backwards when disturbed. Spraying should only be considered in large infestations due to the impact on beneficial insects.


Budworm
Budworm is the term given to cover two different species: the native budworm, Helicoverpa punctigera and the introduced Helicoverpa armigera. Together they are considered to be Australia’s most widespread and destructive caterpillar pest. They also have a number of other common names, such as cotton bollworm, corn earworm, tobacco budworm, tomato fruitworm and tomato grub. As these common names indicate, they attack the buds and fruit of the plants. Prevention is better than cure as once the caterpillars are inside the fruit they are very difficult to control and the damage is done. Homeowners should keep their eyes open for the adult moths, which can be disturbed when watering. Plants can be covered with butterfly netting to prevent the laying of eggs on plants. Whilst the caterpillars are small, they feed on the leaf surface. If spotted at this early stage, a spray with a Bti product can have some benefit. Infested fruit should be removed and as budworms also breed in a number of broadleaf weeds, weed control will also remove potential food sources.


Codling moth
Codling moth, Cydia pomonella, an invasive pest from Europe, is a specific pest of pome fruit (apples and pears), and an extremely difficult pest to control. This is because the caterpillars quickly move from the leaves to bore into the fruit shortly after hatching, making insecticide sprays redundant. Homeowners should keep their eyes open for the adult moths and consider deploying pheromone traps to reduce moth numbers.

