Harlequin Bug: A Pretty Brassica Pest

The harlequin bug, Murgantia histrionica (Hahn) is named for this species’ unique coloration and pattern. The harlequin bug is a member of the stink bug family and has a similar shape and size as other stink bugs; they also produce odors as a defense mechanism against predators. 

Harlequin bug is an invasive pest in North America. Originating from Mexico and Central America, it was introduced to the U.S. after the Civil War. They are commonly found in the southern United States and rarely north of Pennsylvania on the East Coast and Colorado to the west. 

Not only are they invasive pests, but harlequin bugs are also a pest for cruciferous plants such as cabbage, kale, broccoli, mustard greens, and others, earning them the name “harlequin cabbage bugs”. If left unchecked, this pest can cause entire field crops to wilt and die. 

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Harlequin Bug Overview

Harlequin bugs have a distinctive look with their black shield-shaped bodies, speckled with yellow, orange, and red patterns. This aposematic coloration is a form of self-defense to deter predators. They are approximately 8-11.5 mm (3/8 in) in length and the female bugs are slightly larger than the males. It’s no surprise that this bug has captured the imagination of many people who have come up with a range of names for them such as the “calico bug” the “fire bug” and “terrapin back”.

Life Cycle of Harlequin Bugs

Harlequin bugs are destructive pests because they can have up to three generations per year under favorable conditions. One generation or life cycle of harlequin bugs develops over 50-80 days as they undergo the egg stage, nymph instars, and adult stages.  

These bugs overwinter as adults to emerge in early spring every year. Adult females will mate and lay around a dozen black and white eggs per female on the underside of leaves. The eggs are a very recognizable barrel shape standing on their end, marked by two rows of alternating black and white stripes and a black dot. Eggs hatch into nymphs from 4-29 days later depending on the temperature.

Harlequin bug nymphs typically go through 5 or 6 instars and they become more brightly colored with each progressive molt. A newly hatched harlequin bug nymph cannot fly but will develop its wings during the last instar stage.   

Common Habitats

Adults overwinter in leaf litter and debris near their host plants. Annual weeds such as wild mustard, peppergrass, and shepherd’s purse can serve as overwintering hosts. Harlequin bugs are not well adapted to cold winter temperatures which is why they are more commonly a pest in the southern United States. Their population may be especially noticeable after mild winters. Adult harlequin bugs start emerging as soon as the weather warms in early spring and can be found on the leaves of various host plants. Eggs are found on the underside of leaf surfaces. The eggs are easy to spot, black and white striped in color and cylinder-shaped, and they are very easy to identify as harlequin bug eggs on your crops.

What Do Harlequin Bugs Eat?

The harlequin bug (Murgantia histrionica Hahn) feeds on over 50 species of plants but has a strong preference for host plants in the cabbage family, causing them to also be known as the harlequin cabbage bug. Both adults and nymphs feed on plant tissue using their piercing and sucking mouthparts. The damage on leaves looks like light-colored, cloudy, or brown patches of dead plant tissue. 

Harlequin cabbage bug infestations on a large scale will result in large-scale wilting of leaves and stunt the overall development of the plant. Entire crops may suffer or lose market value if they are not able to bounce back from an infestation. A harlequin bug may also feed on other host plants outside of the brassica family including ornamental plants like sweet alyssum and spider plants and fruiting plants like beans, tomatoes, and many others.

How to Control Harlequin Bugs

While gorgeous to look at, these stink bug relatives can cause some serious damage to crops and especially to plants in the brassica family. We recommend using a combination of methods to control their population through an integrated pest management methodology as to not bring harm to beneficial insects in your garden.

Organic or Chemical Control

Even though the harlequin bug is a damaging pest, their adults, nymphs, and eggs can all be easily spotted and destroyed. During the growing season, check your plants frequently, hand-picking and dropping adult harlequin bugs into a cup of soapy water to kill them. Check under the leaves of host plants and crush any harlequin bug eggs that you find there. Hand-picking or even vacuuming bugs can be effective ways to keep the harlequin bug population under control. 

Insecticidal soap can be used against harlequin bugs if the soap covers the bugs completely. The harlequin bug can be controlled chemically using insecticides such as acetamiprid, carbaryl, cyfluthrin, gamma-cyhalothrin, and pyrethrin. 

Some formations of pyrethrin are approved for organic use. Use pyrethrin early in the season and set up a schedule to apply every few weeks. Follow the instructions on the packaging carefully since pyrethrin is a broad-spectrum insecticide.

Spinosad, another type of organic insecticide, has also been shown to be effective against harlequin bug nymphs. 

Environmental Control

Harlequin bugs have relatively few natural enemies because of their self-defense mechanisms through their pungent odors and bright colors. There are three distinct types of native hymenopteran wasps that parasitize the eggs of harlequin bugs: Ooencyrtus johnsoni Howard, Trissolcus murgantiae Ashmead, and Telenomus podisi Ashmead. T. murgantiae has been released in California as a form of biological control and researchers have found parasitized harlequin bug eggs in Virginia as well.

One method of environmental control for harlequin bugs is to grow a few trap crops, like fast-maturing mustards, near your scheduled main crop early in the season. Trap crops can help you identify and destroy the first wave of adults to mitigate against a large infestation later since harlequin bugs use pheromones to congregate on the best food source. Alternate trap crops with a period of non-host plant cultivation to further reduce the overall population of this pest. 

Preventing Harlequin Bugs

A great way to control this pest is by eliminating opportunities for the harlequin bug to survive through the winter. This means cleaning up plant debris and residues from crops like kale or mustard right after harvest. Removing annual weeds around susceptible crops is another way to prevent adult harlequin bugs from overwintering in their vicinity. 

As the weather warms up, add floating row covers around plants to create a physical barrier against harlequin bugs. If you are already using floating row covers to prevent cabbage moths from landing on your brassicas, you are already well equipped to prevent or control harlequin bugs as well. These covers prevent the sucking damage that occurs when a harlequin bug goes to feed; they never reach the plant, so can’t cause the yellow or brown splotches and leaf damage that appears on leaves in their wake.

Frequently Asked Questions

Q: Are harlequin bugs harmful?

A: Yes, harlequin bugs are a common pest in the southern United States and they are particularly damaging to cruciferous plants such as cabbage, kale, mustards, etc. These relatives of stink bugs are very common pests.

Q: What spray kills harlequin bugs?

A: Pyrethrin is a broad-spectrum insecticide that can kill many different bugs upon contact, including harlequin bugs.  It disrupts the nervous system of insects which ultimately leads to their death. Other organic insecticides, such as spinosad, can be used to kill nymphs. Insecticidal soap can also be effective against all stages of the harlequin bug life cycle