Harlequin bug
The harlequin bug is a small stink bug, 1/4 to 3/8 inch (7–11 mm) long, glossy black with bright red, orange or yellow markings. Adults and nymphs suck sap from cabbage, kale, collards, mustard, broccoli and other brassicas, leaving irregular white or cloudy blotches. Heavy feeding makes young plants wilt, turn brown and die. It is mainly a pest of the southern US. Control is physical. Hand-pick adults into soapy water, crush the black-and-white barrel-shaped eggs, remove crop debris after harvest, and use fine insect netting or a mustard trap crop. It stores defensive chemicals from its host plants, advertised by its warning colours, and it has relatively few natural enemies.
Adult harlequin bug (Murgantia histrionica) beside its barrel-shaped eggs on a collard leaf. Photo: pending.
Identification
Adults are shield-shaped, 1/4 to 3/8 inch (7–11 mm) long, and glossy black with vivid red, orange or yellow markings, a pattern bright enough to make them easy to spot on a leaf. Nymphs are smaller and wingless, patterned black, orange and white, and pass through five stages as they grow (UF/IFAS says five or six).
The eggs are the most distinctive stage. Each is a tiny barrel, about 1 mm tall, white or pale with two black bands and a black spot. They stand upright on the underside of leaves in a double row, usually 12 eggs (six by six), and NC State gives 10 to 13.
Damage symptoms
Harlequin bugs pierce the leaves and stems and suck the sap. Each feeding site becomes a pale, cloudy spot. At low numbers the damage is cosmetic, but on leafy greens the leaves are the harvest. Under heavy pressure leaves yellow and wilt, young plants can die, and unsprayed fields can be lost.
- Irregular white or cloudy blotches on the leaves, often many close together
- Leaves that yellow, wilt and brown from the feeding sites
- Young transplants that wilt and die
- Black-and-orange bugs on the undersides of leaves
- Neat double rows of black-and-white barrel-shaped eggs under the leaves
Lifecycle & degree days
Adults spend the winter in crop debris and weeds. In spring they gather on favoured hosts such as mustard and wild radish before moving onto the crop. Egg hatch takes around 20 days in cool early spring and 4 to 5 days in warm weather. A generation takes 50 to 80 days. There are usually two to three generations a year, with a fourth possible in warm places such as south Texas; NC State gives two to four for North Carolina. The bug is not known to overwinter north of about 40° N, which is roughly Colorado and Pennsylvania, though wind-aided migration carries it further north in summer.
- Egg hatch
- 4–29 days, by temperature
- Egg to adult
- 37–57 days at 75 °F (24 °C)
- Eggs per female
- Up to about 155
- Generations / yr
- 2–3 (4 in south Texas); 2–4 in North Carolina
- Overwinters
- Adults, in crop debris and weeds
Host crops
Harlequin bugs feed on nearly all crucifers, including cabbage, collards, kale, mustard, broccoli, cauliflower, Brussels sprouts, turnip, kohlrabi, radish and horseradish, as well as ornamental cleome, flowering kale and stock. Mustard is strongly preferred, which is why it works as a trap crop. When the preferred hosts are scarce the bugs also feed on squash, beans, tomato, potato, eggplant, okra, corn and asparagus. Wild mustards, shepherd's purse, peppergrass and bittercress keep them going between crops.
Monitoring & action thresholds
None of the extension sources reviewed gives a numeric threshold for gardens. At low numbers the damage is cosmetic. On leafy greens, and on young transplants that can be killed, act as soon as you see adults or egg clusters.
From early spring, check the undersides of leaves for adults and for the double-row egg clusters, starting with any mustard, early brassicas or wild mustard nearby, where the first bugs gather. Keep checking every week through the season, because the generations overlap.
Biological control
Harlequin bugs have relatively few natural enemies. The bugs take up defensive chemicals (glucosinolates) from the brassicas they feed on, and their warning colours advertise it. Three native wasps parasitise the eggs: Trissolcus murgantiae, Ooencyrtus johnsoni and Telenomus podisi. A Virginia survey found T. podisi in 63.5% of egg masses but only 12.9% of the eggs, and historical rates range from 8 to 50% of eggs by pest density. None of these wasps has a profile here yet.
Cultural controls
Physical control and good timing are what work in a garden. In a two-year University of Kentucky field trial on broccoli (published 2024), fine insect netting gave the best protection of anything tested. Among the sprays, only the spinosad product Entrust came close, and none of the essential-oil or bokashi products was effective.
- Cover young brassicas with fine insect netting. In the Kentucky trial it gave the best control and the highest yield
- Hand-pick adults and nymphs into a jar of soapy water, and crush egg clusters on the leaf undersides
- Plant mustard greens as a trap crop, set a few feet apart from the main crop. In a USDA autumn field trial, a 2.3 m (7.5 ft) gap cut egg-laying on collards fourfold compared with an adjacent strip
- Pull or destroy the trap crop, with the bugs on it, before they move to the main crop
- Remove and destroy crop debris after harvest to take away the overwintering shelter
- Wild mustards, shepherd's purse and other cruciferous weeds are hosts, so keep them down around the beds
Chemical, last resort
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Wallingford et al., Harlequin Bug Biology and Pest Management in Brassicaceous Crops, J. Integr. Pest Mgmt 2011
NC State Extension, Harlequin Bug (J. Baker, revised 2025)
UF/IFAS Featured Creatures IN152, Harlequin Bug (M.A. Knox)
Wallingford et al., Host plant preference of harlequin bug … trap cropping in collard, J. Econ. Entomol. 2013
Bier et al., Trap Cropping Harlequin Bug: Distance of Separation …, J. Econ. Entomol. 2021
Clark et al., Evaluation of Ten Alternative Treatments for … Harlequin Bug, Plants 2024
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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