Caterpillars

Caterpillars ‚Äď an overview:

This page provides an overview of caterpillar pests in vegetable crops. The related tools listed at the end of the page provide detailed information about their identification, damage, and management. It is important to be able to identify the different life stages of the species whose caterpillars are pests, and to have unknown species expertly identified so that they can be appropriately managed.

Caterpillars are a major pest to vegetable crops as they are voracious feeders and cause extensive damage to leaves and fruits of crops they feed on. They usually thrive in warm conditions, with pest pressure increasing during the summer months. Warm weather increases the rate and speed of hatching and development of caterpillars. Control is best achieved using an IPM approach.

Caterpillar species, hosts, and damage:

Below are key species whose caterpillars (larvae) may cause significant damage to vegetable crops. The appearance of caterpillars may change as they mature. Other important species include Cucumber moth (Bacterocera cucumis), Lucerne leafroller (Merophyas divulsana) and Potato moth (Phthorimaea operculella).

Caterpillar species

Description

Host vegetable crops

Primary damage

Diamondback moth (DBM) (Plutella xylostella) Caterpillars are light brown at hatching and bright green when fully grown. Brassica vegetables ‚Äď broccoli; cauliflower; cabbage; Brussels sprouts; Asian leafy brassicas (e.g. bok choy, gai lan). Most destructive insect pest of Brassica crops worldwide. Eats holes in leaves (making feeding windows by leaving the upper surface of the leaf intact), tunnels into heads, and contaminates produce by pupating inside broccoli florets and cauliflower curds
Loopers (Chrysodeixis spp.) Caterpillars are green and move with a distinctive looping action. Leafy vegetables; brassica vegetables; greenhouse vegetables; beans; tomatoes; potatoes. Chew large ragged holes in leaves and bore into the heads of crops. May also feed on flowers and pods.
Heliothis: Corn earworm (Helicoverpa armigera) or Native budworm (Helicoverpa punctigera) Older caterpillars vary in colour and can be green, pink, buff, or brown. They have distinct side stripes and visible hairs. Sweet corn; beans; peas; lettuce; brassica vegetables; greenhouse vegetables; wide range of crops. In sweet corn, Heliothis caterpillars chew leaves and tunnel down the silk channel of the cob to chew the kernels. Feed on leaves, buds, flowers and pods. Older caterpillars burrow into fruit, pods, and heads of crops.
Cutworm (Agrotis spp.) Caterpillars are usually dark-grey to brown in colour. When disturbed they curl into a distinct 'C' shape. Brassica vegetables; leafy vegetables; cucurbit vegetables; beans; parsley. Small caterpillars skeletonise leaves or leave small holes. Older caterpillars feed on stems and may cut off seedling stems at ground level.
Cluster caterpillar (Spodoptera litura)  Caterpillars vary in colour from green to brownish purple, with a row of triangular spots on each side of the body.  Brassica vegetables; leafy vegetables; tomatoes; leeks;beans; wide range of crops. Young larvae feed close together and skeletonise leaves. Older larvae feed separately and chew holes in leaves
 Cabbage cluster caterpillar (Crocidolomia pavonana)  Young caterpillars are cream-coloured, but become light green with yellowish stripes as they grow.  Brassica vegetables. Caterpillars feed in groups and eat large amounts of leaf material. Cabbage heads become covered with webbing and frass (droppings).
 Cabbage white butterfly (Pieris rapae)  At hatching caterpillars are orange but become a dark velvety green with a thin yellow stripe on sides and on top.  Brassica vegetables. Large irregular areas of the leaf edge are eaten. Dark green caterpillar droppings contaminate leaves.
 Cabbage centre grub (Hellula hydralis)  Fully grown caterpillars are thickset and cream with reddish-brown stripes.  Brassica vegetables.  Damage terminal buds, with frass and silk webbing present. Leaves may be webbed together or develop large blisters.

Pest management:

To control caterpillars there are a range of cultural, biological and chemical options available. It is important to identify and monitor populations of both pests and beneficials, including eggs, small larvae and adults. It is also crucial to understand the environmental conditions conducive to development, know your acceptable limits for damage, and be able to identify when you may need to spray.

The adoption of Integrated Pest Management (IPM) has become crucial because of insecticide resistance and the unwanted effects that broad-spectrum insecticides have on natural enemies. IPM uses a range of control measures to keep pest numbers below the level where they are causing damage. IPM primarily relies on monitoring the crop regularly and making strategic control decisions according to established damage thresholds.

Biological:

There are a number of naturally occurring beneficials which attack moth eggs, caterpillars and pupa. These include parasitoids (e.g. Trichogramma spp. and Tachinid flies), predatory bugs, spiders, lacewings, ladybird beetles and other predatory beetles. An IPM program identifies and conserves these natural enemies.

Chemical:

Chemical control measures should be managed carefully to reduce the development of resistance and not harm beneficials. DBM and Helicoverpa armigera populations have developed resistance to broad spectrum insecticides and their use should be limited. Biopesticides (Bt and NPV) and soft option insecticides are available. NPV only affects Heliothis caterpillars. Bt only works well against smaller caterpillars and stops caterpillar feeding but takes several days to kill. Insecticide Resistance Management (IRM) strategies should be used. It is highly recommended that growers use the Insecticide Toxicity Chart (available at the SARDI website) and CropLife Australia’s IRMRG Two-window strategy to consolidate their IPM and IRM programs.

Cultural:

Infestation risk factors can be significantly reduced with good farm and crop hygiene. Planting should be done with spacing that allows for maximum spray coverage; rotate crops to minimise pest pressure; select a production period that will minimise pest pressure; use strategic cultivation and ‚Äėpupae busting‚Äô; and control weeds.

Source of information and related tools: