Imported Cabbage Worm
Pieris rapae
📖 Description
The imported cabbage worm is the larval stage of the cabbage white butterfly, one of the most common butterflies in temperate regions worldwide. Despite its delicate appearance, this butterfly is one of the most destructive pests of brassica crops, capable of reducing cabbage, broccoli, and kale to nothing but stems in a matter of days. The green caterpillars are perfectly camouflaged against the foliage and often go unnoticed until significant damage has been done. The white butterflies are active from early spring through fall, laying eggs continuously, which means multiple overlapping generations attack crops throughout the entire growing season. This pest is particularly frustrating for home gardeners because the caterpillars hide deep within broccoli and cauliflower heads, making them difficult to detect and remove before cooking.
⚠️ Symptoms to watch for
- Large irregular holes chewed in leaves
- Green frass (droppings) on and between leaves
- Chewed growing tips and heart of cabbage heads
- White butterflies fluttering over brassica crops
- Skeletonized outer leaves with only veins remaining
- Contamination of broccoli and cauliflower heads with caterpillars
🩹 Treatment
- Hand-pick green caterpillars from leaves (organic)
- Apply Bt (Bacillus thuringiensis kurstaki) every 7-10 days (organic)
- Release Trichogramma wasps to parasitize eggs (organic)
- Use spinosad-based spray for heavier infestations (organic)
- Apply neem oil as a feeding deterrent (organic)
- Use permethrin or carbaryl spray (chemical)
🌿 Organic treatments
- Hand-pick green caterpillars from leaves
- Apply Bt (Bacillus thuringiensis kurstaki) every 7-10 days
- Release Trichogramma wasps to parasitize eggs
- Use spinosad-based spray for heavier infestations
- Apply neem oil as a feeding deterrent
🧪 Chemical treatments
- Use permethrin or carbaryl spray
🛡️ Prevention
- Use floating row covers immediately after planting
- Plant red-leafed varieties that are less attractive to butterflies
- Intercrop with aromatic herbs like thyme
- sage
- or mint
- Remove crop debris after harvest to eliminate overwintering pupae
- Check leaf undersides for tiny yellow eggs and crush them
- Encourage native parasitic wasps by planting nectar flowers
🪴 Affected plants
- Cabbage
- Broccoli
- Cauliflower
- Kale
- Brussels Sprouts
- Radishes
- Mustard Greens
🦋 Natural predators
- Parasitic Wasps
- Birds
- Spiders
🌱 Host plants
- Brassica oleracea
- Brassica rapa
- Raphanus sativus
🔄 Lifecycle
- Adults emerge in early spring and begin laying eggs within days.
- Females lay 300-400 eggs singly on leaf undersides over 2-3 weeks.
- Eggs hatch in 3-7 days.
- Caterpillars feed for 2-3 weeks through 5 instar stages, then pupate on plant stems, fence posts, or debris.
- Pupation takes 7-14 days.
- Three to five overlapping generations per year depending on climate.
- Overwinter as pupae attached to plant debris and structures.
- Adults are strong fliers and active on warm sunny days.
📅 Season
- Spring through Fall (multiple generations)
🔎 Appearance
- Larvae are velvety green caterpillars with a faint yellow stripe down the back and a row of yellow spots along each side.
- They blend in perfectly with cabbage and broccoli leaves.
- Adults are white butterflies with one or two black spots on each forewing, commonly seen fluttering over vegetable gardens.
💥 Damage level
- High
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- North America
- Europe
- Asia
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