Caterpillars are the larvae of moths and butterflies. Many of them, such as Leafroller caterpillars, Looper caterpillars, White Butterfly caterpillars, Diamond Back Moth caterpillars, Tomato Fruit Worm, Raspberry Bud Moth and Fall Webworm are well known to gardeners trying to grow fruit, vegetables or other plants. Caterpillars are voracious eaters. They can be regarded as eating machines whose sole purpose in life is to eat and grow to a point where they have enough energy stored to enable them to pupate and emerge as the adult butterfly or moth. The adults in turn are mating machines whose purpose is to find and mate and for females to lay more eggs. The problem for gardeners and commercial growers is that they eat the leaves of crops and ornamental plants.
I like butterflies and would encourage you to grow plants in your garden specifically as food for native butterflies. Grow swan plants to feed the Monarch caterpillars or Kowhai to feed Kowhai moth caterpillar. But because when we cultivate crops, many plants of the same type grown in the same place give the pest caterpillar species that prefer these plants an unnatural feast. Numbers can explode to plague-like proportions, devouring all your hard work.
How to prevent caterpillars eating your vegetables and fruit.
Chemical insecticides can be sprayed or dusted on vegetables and fruit to kill caterpillars that might eat them. But most such insecticides will have withholding periods where the fruit or vegetables cannot be eaten after treatment. Many people would prefer to protect the crops without the use of a chemical insecticide.
Luckily, the gut of insect larvae such as caterpillars is unusual in that it is alkaline rather than acidic and the naturally occurring soil bacterium Bacillus thuringiensis kurtsaki (Btk) will grow in the alkaline gut. Here in the presence of insect specific gut enzymes it produces proteins that are toxic to the caterpillars.
Kiwicare Organic Insect Control pyrethrum is effective on caterpillars, can be used on fruit and vegetables, and has only a one day withholding period.
Organic Caterpillar Bio-Control controls pest insect caterpillars and other leaf eating larvae on fruit, vegetables and ornamentals. It is safe to handle, does not affect the plants or beneficial insect species but is deadly to plant damaging caterpillars when used as directed. It will control all types of caterpillars including leafroller, looper and white butterfly as well as diamond back moth larvae, tomato fruitworm, and fall webworm. Beneficial insects such as ladybirds and bees are not harmed.
If possible apply to plants when caterpillars are young, before plant damage occurs. Shake your sprayer regularly to prevent settling. Spray to the point of run off (i.e. liquid begins to run off leaves). Thorough coverage is essential so try and spray undersides of leaves as well as top. Repeat spraying every 10-14 days.
Make sure you enjoy your summer fruit and vegetables and not the caterpillars.