Lepidoptera

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Image above: caterpillar stage of the Oleander Butterfly

Caterpillars are the larvae of moths and butterflies of the order Lepidoptera. There are more than 20,000 species which occur in Australia, but only half have been scientifically named. Only about 400 of these species are butterflies – the rest are moths. That means there are almost as many species of moths in Australia as there are native plant species.


Moths and butterflies usually have proboscises to suck nectar from flowers, while their larvae have chewing mouthparts. The larvae of pest species can inflict considerable damage to plants. Luckily not all caterpillars are pests. Out of the thousands of caterpillars out there, only about 50 can be considered pests.

Best Treatment for Caterpillars

The first thing you need to do when you see caterpillars on a plant is identify them. If it’s a serious pest species, you may need to control the caterpillars, if it is not a pest species you may be able to tolerate the damage. For example, you might tolerate a few caterpillars of the Orchard Swallowtail (Papilio aegus) feeding on the leaves of your lemon tree, so that you can enjoy the beautiful butterflies later. You might tolerate the massive and colourful caterpillars of the Emperor Gum Moth (Opodiphthera eucalypti) feeding on a young gum tree, so that you can boost the declining numbers of their iconic adult moths.

There are plenty of ways to combat pest caterpillars. The secret to pest control is to keep an eye on your plants, so that you can detect pest caterpillars early. After a while you will become familiar with what caterpillar damage looks like (see Symptoms of Caterpillar Damage). If you find damage, you should have a closer look to see if you can find some caterpillars and work out what they are.

If you routinely get incursions of pest caterpillars, there are several things you can do to prevent serious damage (see How to Prevent Caterpillars Appearing).

Regular monitoring of your garden will ensure that a major infestation of Caterpillars doesn’t occur ‘overnight’. All treatments are way more effective if you can catch an infestation in its early stages. To treat, try Yates Nature’s Way Caterpillar Killer - Dipel. The product is based on naturally occurring bacteria (Bacillus thuringiensis) which acts as a stomach poison against caterpillars. The product will only affect caterpillars, so your ‘good bugs’ are safe. Follow the label directions and it will work against Caterpillars in your garden. Or you could try Yates Nature's Way Citrus & Ornamental Spray.

If you need prefer a quick ready-to-use spray, try Yates Pyrethrum Pest Gun. It can be used to treat caterpillars on a wide range of plants, including vegetable, fruit trees, flowers and ornamental plants. Yates Pyrethrum Pest Gun is based on the natural pyrethrum daisy extract and works on contact to knock down caterpillars and other insect pests.

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Image above: Painted Apple Moth caterpillar
(Image courtesy of Elise Dando)

What are Caterpillars &
How to Get Rid of Them

Caterpillars are the larvae of moths or butterflies of the insect order Lepidoptera. Caterpillars are incredibly diverse in their anatomical forms, their feeding habits and their behaviour. Caterpillars have various common names depending on the species involved – for example, inchworm, armyworm, woolly bear, looper, and cutworm.

The caterpillar stage is the only time that moths and butterflies grow. When caterpillars first hatch from an egg, they are tiny (approximately 1 mm long), but to grow larger the caterpillars need to moult. As a caterpillar feeds, it expands, and the skin stretches and eventually splits. After emerging from the split skin, the now larger caterpillar is usually pale in colour for a few hours, until its new skin hardens and resumes its usual colour. Each growth stage is known as an ‘instar’ and there are always several instars before pupation. Once an adult moth or butterfly emerges from a pupa it does not grow.

Depending on the Lepidoptera species involved, caterpillars may feed on any part of a plant – flowers, leaves, bark, stems, fruit, trunk or roots. They may feed openly during the day, or only feed at night, or they may feed out of sight by tunnelling into various plant parts. The thing to note about pest species of caterpillars, is that they eat 90% of the food they will ever eat in the final instar of their larval stage. If you have pest caterpillars in your garden, it is best to control them at an early instar, therefore, when they are small.

 

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Image above: Small Citrus Butterfly chewing citrus leaves
(image courtesy of Elise Dando)


Description

Adults

Moths and butterflies form the order Lepidoptera, a word which means lepís ‘scale’ + pterón ‘wing’, therefore, ‘scaly wings’. The wings of moths and butterflies are covered with tiny overlapping scales, as are the head and parts of the thorax and abdomen.

The scales give the insects their colour, either through the pigments contained in the scales or by structural colouration (such as diffraction). Scales also provide insulation, which has allowed moths to become the dominant night flying insect.

Moths and butterflies have a proboscis, which they use to extract nectar from flowers. When not in use, the proboscis curls up neatly under their heads. 

In the insect world there are always oddities. There are wingless moths (such as female Case Moths), and some moths don’t have proboscises and don’t feed at all (such as Emperor Gum Moths).

What is the difference between a moth and a butterfly? Butterflies always have antennae with a club at the tip, while moths usually have feathery or thread-like antennae. Butterflies usually hold their wings upright when resting, unless they are sunning themselves, while moths usually fold theirs down.

Do moths only fly at night? No, some species such as the Grapevine Moth, aka Vine Moth (Phalaenoides glycinae) are day-flying moths. Grapevine Moths are black moths with yellow or white wing markings with a wingspan of about 50 mm. They have tufts of bright orange hairs on the tip of their abdomen and at the base of their legs. Males and females are not easy to tell apart unless you examine the tip of their abdomen – it is squarish in males and tapered in females. Grapevine Moth is found in south-eastern Australia including SE Queensland, New South Wales, Victoria, Tasmania and South Australia.


Larvae

Most caterpillars (larvae) usually take the form of an elongated fleshy tube with legs. Caterpillars have three pairs of thoracic legs, which are located just behind the head. They also have a varying number of fleshy barrel-shaped abdominal legs or ‘prolegs’. These prolegs are very useful for gripping a stem while feeding. Most caterpillars have four pairs of prolegs, but ‘looper’ caterpillars have only two pairs which results in a characteristic ‘looping’ gait.

The head of caterpillars is dominated by what look like two huge eyes but is actually the epicranium or ‘head capsule’ of the caterpillar. The head capsule is divided by an inverted Y-shaped line extending down from the top of the head. This Y-shaped line distinguishes caterpillars from any other insect larva – for example, beetle or sawfly.

Caterpillars have simple eyes (known as ‘stemmata’) which are only capable of distinguishing between dark and light, giving the caterpillars some spatial awareness. Caterpillars have six stemmata, which are inconspicuous raised dots, located on each side of the head capsule.

When caterpillars moult, they usually eat their old skin, but discard the old hardened head capsule. Larvae of the Gum-leaf Skeletoniser Moth (Uraba lugens) keep their old head capsule and stack it on top of the new one. After a few moults, the caterpillars have conspicuous pointy hats. These caterpillars are great favourites of children who call them ‘haterpillars’.

The Gum-leaf Skeletoniser caterpillar is also very hairy, and those hairs can irritate the skin of some people. Mature Grapevine Moth (Phalaenoides glycinae) larvae are mostly smooth and fleshy with a few hairs. Grapevine Moth larvae are conspicuous black-and-white patterned caterpillars up to 50 mm in length, with a pink hump and small pink markings on the sides.


Life Cycle

Moths and butterflies grow through a life cycle of complete metamorphosis – egg, larva, pupa adult. Depending on the species involved, female moths or butterflies may lay their eggs on or into plant tissue, and they may lay eggs singly or in batches.

Grapevine Moth has a typical life cycle. Eggs are laid on stems and leaves and hatching larvae develop through six larval instars. Final instar larvae leave the food plant and wander for a couple of days before pupating in a silk lined cell in the ground or cracks in vine wood or fence posts. There can be as many as three generations per year depending on the climate.

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Image above: Lily caterpillars

What Plants are Impacted by Caterpillars

Caterpillars feed on a vast range of plants. Sometimes their common name reflects what a caterpillar feeds on, for example, Cycad Blue Butterfly, Lawn Armyworm, Cabbage Moth, Soybean Looper, etc.

The Grapevine Moth is a native moth that feeds on a range of native plants, including Guinea flower (Hibbertia) and purple coral pea (Hardenbergia), but took a liking to grapevines and other ornamental plants such as fuchsias when they were first brought to Australia.

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Image above: Leaf skeletonised by caterpillars chewing between leaf veins
(Image courtesy of Elise Dando)

Symptoms of Caterpillar Damage

  • Defoliation is one of the most obvious and dramatic symptoms of a caterpillar infestation on a plant.
  • More subtle symptoms include leaf edge scalloping, small holes in leaves, and skeletonised leaves.
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Image above: Chewed holes in silverbeet leaves made by caterpillars
(Image courtesy of Elise Dando)

How to Prevent Caterpillars Appearing

Monitor

  • Watch for moths and butterflies fluttering around susceptible plants.

Prevent

  • Net plants where practical, with a weave small enough to stop moths or butterflies of pest species laying eggs on your plants.
  • Break the life cycle by picking off leaves with eggs or small caterpillars (early instars) on them. Pick off large caterpillars (final instar) if there are not too many.

Natural enemies

  • Many species of parasitic wasps and flies. Some parasites are specific to certain pest caterpillars.
  • Predators such as damsel bugs, assassin bugs, predatory shield bugs, ladybird beetles and lacewing larvae.

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Lawn Armyworm

Lawn Armyworm is an introduced species and is a major pest of gardens. Caterpillars - the damage-causing stage of the Lawn Armyworm lifecycle - predominantly feed on tender new growth of leaves and seedlings.