Caterpillars (general)
Role in the garden
Butterfly larvae that devour leaves, flowers and fruit. Not all are harmful, but some cause major damage to crops.
Practical guide
Where to find them
Cabbages, turnips and nasturtiums for the cabbage whites; fruit trees, tomato and many vegetables for other species (noctuids, tortrix moths).
Prevention
Set up an insect net from the start. Encourage insectivorous birds (tits) by putting up nest boxes: in an orchard, great tits modestly reduced caterpillar damage (Mols & Visser, 2002).
Early signs
Holes in the leaves; plants are sometimes reduced to their stems. Risk of confusion with slug damage: look closely to catch the caterpillars in the act, and search for clusters of yellow eggs under the leaves.
Action / control
Gather the caterpillars and the egg clusters you spot every day. Targeted Bacillus thuringiensis in case of heavy infestation.
Sources
- RHS (Royal Horticultural Society) : Cabbage caterpillars (rhs.org.uk/biodiversity/cabbage-caterpillars)
- Mols, C.M.M. & Visser, M.E. (2002). Great tits can reduce caterpillar damage in apple orchards. Journal of Applied Ecology, 39(6), 888-899.
- UC IPM (université de Californie) : Less Toxic Insecticides (ipm.ucanr.edu)