Caterpillar Pests?

How do I get rid of Caterpillar pests? Don Herbison-Evans,
( donherbisonevans@yahoo.com)
and
Stella Crossley

In the house: There are often eggs of some pest species in flour, meusli, cereals, and dried fruit. Check for silk in these items after you have had them a week or two. Silk threads mean that caterpillars are there. Once these caterpillars have gone through their life cycle, which might be only a few weeks in a warm household, the adult moths will fly around the house to lay their eggs in any of your foods that are accessible. Stop the moths from accessing your food. Always keep all foods either in plastic or glass containers with airtight lids, or in the fridge. Clean all surfaces (benches, walls, ceilings, cracks between these) of any spilled foodstuff, removing especially the thin surface layer of oil that might deposit from vapours when frying. Screen all windows and doors to stop adults coming in at night to lay more eggs.

On a house plant: Lift the Caterpillars off and kill them. The hairs on some Caterpillars can cause an allegic reaction, so it may be wise to use forceps or gloves to avoid direct skin contact with the beasties. Some Caterpillars live at the base of the plant and crawl upwards to feed at night. Therefore inspect the plant in daylight and later at night in darkness with a torch.

In the garden: This same method is useful for a few small plants. For a large bed, put sacking along between the rows. The Caterpillars will shelter there and can be caught.

On a large plant such as a tree: Ignore them. Trees are good at surviving an occassional defoliation, and next year there are likely to more predators around to control the pest naturally.

In the lawn: This is difficult. You could go around collecting them into a bucket, or if you have a big lawn, you could run over it with a heavy roller. Some lawn pests are nocturnal. Try collecting/rolling around midnight, or leave out some sacking for them to hide under by day where you can collect them.

Caterpillars in fruit on a fruit tree: Insecticides are inclined to kill pollinating insects as well as the pests. Timing is critical. Knowledge of the life cycle of the Caterpillar is necessary to prevent infestation. If the female moth is flightless, she can be prevented from reaching the fruit by wrapping a sticky band around the tree. Sticky bands are also used to prevent Caterpillars from reaching the soil where they pupate, so reducing infestation next year.

Borers in trunks and branches: The only hope is to inject the trees with a systemic insecticide: bore a thin hole in the trunk and inject it with an eyedropper. Most native shrubs in Australia have their lives limited to about 10 yrs because of borers. The long term solution is to keep planting young replacements every 5 years so that there are mature plants on a rotating basis.

Mycalesis perseus vs Praying Mantid
(Photo: courtesy of Jeevan Jose)

On farms and nurseries: Long term solutions are biological: finding viruses, bacteria, and predators that attack the particular pest Caterpillar species. For example, preparations based on the bacterium Bacillus thuringiensis are very selective and only kill Lepidoptera larvae. We do not advise using general insecticides because not only do they kill the pest caterpillars but they also kill the predators that control the pest naturally such as spiders, parasitic wasps and flies. This means that in subsequent years, the problem will probably get worse.

Caterpillar vs Wasp
(Photo: courtesy of Trevor Jinks)

Do not be worried about long-term damage if there is a sudden surge in the population of a particular pest one year. The predator/prey relationships cause acyclic population changes, which can include rare single year population bursts preceded by and followed by many years of low population,
eg the sudden burst of Cephonodes kingii on Gardenias in 2001 in Australia.

So if there was no big infestation in previous years, it is wiser in the long term just let the predators have a bumper year, and then they will control the pest better next year. Particularly for deciduous trees: bear in mind that these trees are adapted to defoliation every winter, and one early year is unlikely to cause permanent damage.

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(updated 19 May 2002, 13 October 2017)