Description of the Pest
The redhumped caterpillar has a distinctive appearance. The color of its body is yellow and is marked by longitudinal reddish and white stripes, its 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 spring and early summer, moths lay egg masses on the undersides of leaves. Eggs hatch into larvae that feed on leaves in April or May. There are at least three generations each year in northern California.
Damage
Redhumped caterpillars skeletonize leaves, leaving behind only leaf veins. They do not leave webbing on leaves.
Management
Redhumped caterpillar can be a pest of prune orchards in the Central Valley. Biological control and pruning are often sufficient to manage the pest. Use the monitoring guidelines below to determine need for treatment.
Biological Control
Several natural enemies attack redhumped caterpillars, frequently preventing them from becoming destructive pests. Most common are two parasitoid wasps: Hyposoter fugitivus, which forms a single pupal case that is white with a black band around the middle, and a species of Cotesia, which forms a fluffy white mass of pupal cases. Several general predators, including spiders, green lacewings, brown lacewings, bigeyed bugs, and damsel bugs, occasionally feed on caterpillar eggs and small larvae.
Cultural Control
On small trees, cut out and destroy infested twigs.
Organically Acceptable Methods
Use biological control, cultural control, Bacillus thuringiensis ssp. kurstaki (Bt), and the Entrust formulation of spinosad in a certified organic crop.
Monitoring and Treatment Decisions
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 deciding if the insecticide application is needed. Look for parasite pupae among redhumped caterpillar larval colonies. If 80% or more of larvae are 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 Bt are effective against the larvae.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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DiPel DF # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
11A |
Label rates | 4 | 0 | Most effective on small caterpillars. Do... | narrow | low | low | low | none | — | — | — | — | — | 12/2025 | ||
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|
Intrepid 2F | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
18 |
8–16 fl oz | 4 | 7 | Methoxyfenozide has little or no effect... | narrow | low | low | low | none | very low | low | low | very low | low | 12/2025 | ||
|
|
Delegate WG | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
3–7 oz | 4 | 1 | Apply only during late evening, night, o... | narrow | low | moderate | low/moderate | moderate | low | low | low | very low | low | 12/2025 | ||
|
|
Entrust # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
1.71–2.5 oz | 4 | 7 | Apply only during late evening, night, o... | narrow | low | moderate 13 | low/moderate | short | very low | low | low | very low | low | 12/2025 | ||
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|
Success | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
6–8 fl oz | 4 | 7 | Apply only during late evening, night, o... | narrow | low | moderate 13 | low/moderate | short | very low | low | low | very low | low | 12/2025 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b Toxic to some natural enemies (lacewing and syrphid fly larvae, predatory beetles, and thrips) when sprayed and up to 5 to 7 days after.
UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
C. Pickel (emeritus), UC IPM and UC Cooperative Extension Sutter and Yuba counties
F.J.A. Niederholzer, UC Cooperative Extension Sutter/Yuba counties
W.H. Olson, UC Cooperative Extension Butte County
F.G. Zalom (emeritus), Entomology, UC Davis
R.P. Buchner (emeritus), UC Cooperative Extension Tehama County
W.H. Krueger (emeritus), UC Cooperative Extension Glenn County
Acknowledgement for Contributions to Invertebrates
W.O. Reil (emeritus), UC Cooperative Extension Solano and Yolo counties
