How to Manage Pests
UC Pest Management Guidelines
Scientific name: Schizura concinna
(Reviewed 10/14, updated 10/14)
In this Guideline:
DESCRIPTION OF THE PEST
The redhumped caterpillar is easily recognized because of its striking appearance: the main body color is yellow and is marked by longitudinal reddish and white stripes; the head is bright red, and the fourth abdominal segment is red and enlarged. Redhumped caterpillars pass the winter as full-grown larvae in cocoons on the ground. In early summer, moths lay egg masses on the undersides of leaves. Eggs hatch into larvae that feed in groups on leaves. There are at least three generations each year in Northern California.
Redhumped caterpillars generally skeletonize leaves, leaving behind only leaf veins. They do not web leaves.
Redhumped caterpillar can be a pest of apricot orchards in the Central Valley; it is not usually found in Central Coast orchards. Biological control and pruning is often sufficient to manage the pest; use the monitoring guidelines below to determine need for treatment.
A number of natural enemies attack redhumped caterpillars, frequently preventing them from becoming destructive pests. Most common are two parasitic wasps, Hyposoter fugitivus, and a species of Cotesia (=Apanteles). Several general predators, including spiders, lacewings, bigeyed bugs, and damsel bugs occasionally feed on caterpillar eggs and small larvae.
On small trees, cut out and destroy infested twigs.
Organically Acceptable Methods
Use cultural and biological control, as well as sprays of Bacillus thuringiensis, and the Entrust formulation of spinosad on organically grown apricots.
Begin looking for redhumped caterpillars in May, when eggs or larvae of the first generation may be present. Check trees throughout the orchard, looking at the undersides of leaves for egg masses or groups of small larvae. Skeletonized leaves that turn brown may indicate the presence of redhumped caterpillars. If you find larvae of the first generation, do not treat. Prune out and destroy localized infestations.
Monitor again in July for second-generation larvae and for the presence of parasites before you make a treatment decision. Look for parasite pupae among larval colonies. Caterpillar larvae parasitized by Cotesia have numerous small, white, fluffy tubes protruding from their bodies. Caterpillars parasitized by Hyposoter have a thin, gray pupa attached by a tiny cord to their desiccating bodies.
If 80% or more of the larval population is parasitized, no treatment is needed. If parasitization is very low, prune out and destroy infestations or treat infested trees. Infestations tend to be very localized, so spot treatments usually suffice. Formulations of Bacillus thuringiensis are effective against the larvae.
UC IPM Pest Management Guidelines:
Insects and Mites
W. W. Coates, UC Cooperative Extension, San Benito County
Acknowledgment for contributions to Insects and Mites:L. C. Hendricks, UC Cooperative Extension, Merced County