Chewing and biting pests: an overview
Chewing and biting pests bite into and chew the leaves, stems, buds, flowers, and even the roots of plants. Damage caused by these insects includes holes in the leaves or stems; semicircular holes along the edges of the leaves; discolouration on the surface or the edges of the foliage and flower petal; severed stems and leaves; and plant wilting.
The caterpillars of some of these pests are very destructive and difficult to control for a number of reasons including the development of resistance to chemicals, rapid population increases, and the practical difficulties of achieving complete spray coverage in some at-risk crops (e.g. sweet corn, Brassica vegetables, and lettuce).
Examples include:
Chewing and biting pests include Helicoverpa and diamondback moth (DBM), caterpillars, beetles, and slugs and snails.
What attracts these pests?
Warm, humid weather and developing crops – including sweet corn, Brassica vegetables, and lettuce – provide the perfect environment for DBM and Heliothis (Helicoverpa). The continuous presence of susceptible hosts in combination with the overuse of broad spectrum synthetic chemicals (and resultant chemical resistance) has given rise to more reports of poor pest control, variable produce quality, and the resultant loss of income.
How can I manage these pests?
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Start looking, monitoring, and recording your observations
Examine incoming transplants and make sure they are clean and free of eggs and larvae. Scouting is particularly important in lettuce and brassicas because every part of these plants - in all stages of their development - is subject to attack. Weather monitoring is also important as temperatures affect the generation times of pests and beneficials that have been introduced. -
Start early
Wireworms, cutworms, and armyworms attack newly transplanted and emerging crops. Therefore, it is important to walk through crops and investigate the cause of any recent damage, turning over leaves, looking for eggs. Set up pheromone and moth traps as they can be used to give early warning of the presence of some pests. -
Know what to look for
Finding viable heliothis eggs should trigger crop protection activity. The appearance of the eggs provides predictive information useful in decision-making about the timing of the crop protection activity. Newly laid eggs are white in colour, brown eggs are nearing hatching, and shiny black eggs are parasitised and unlikely to hatch. Treatments are needed before larvae burrow into the parts of developing crops, where they are impossible to treat. -
Scout at the heart stage for lettuce and brassica crops
This requires cutting open the heads to check for caterpillars. Sampling charts are useful as they provide a guide to the minimum number of plants to be checked to give confidence that the results from them are valid and representative of the whole block. -
Understand damage thresholds, pest lifecycles the stages at which crops are most at risk
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Limit the use of broad spectrum insecticides and instead use biopesticides (Bacillus thuringiensis and the nuclear polyhedrosis virus) and soft option insecticides.
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Use beneficial organisms
Parasitoid wasps and predatory bugs readily control caterpillars. Spiders, lacewings, and ladybird beetles feed on moth eggs and caterpillars, and also offer relief against aphids and thrips. -
Soil monitoring for over-wintering heliothis pupae
IPM tips for managing chewing and biting insects:
- Use resistant varieties
- Consider a production break, especially in brassica production regions
- Identify and monitor the populations of both pests and beneficials – including eggs, small larvae, and adults
- Understand all available management options including effective biopesticides that do not disrupt natural enemies
- Don't rely on synthetic insecticides for control and rotate between pesticide groups to avoid resistance
- Understand conducive environmental conditions – for pests, beneficials, and biopesticide performance
- Disrupt pest life cycles by targeting overwintering and survival sites
- Know your acceptable limits of crop damage and identify when you may need to spray.