Harlequin Bug: A fairly Brassica plague

The harlequin bug Murgantia histrionica (rooster) is named after the unique color and pattern of this species. The harlequin bug belongs to the stink bug family and is similar in shape and size to other stink bugs; they also produce odors as a defense mechanism against predators.

Harlequin bug is an invasive pest found in North America. Originally from Mexico and Central America, it was introduced to the United States after the Civil War. They are common in the southern United States and rarely found north of Pennsylvania on the east coast and Colorado in the west.

Harlequin beetles are not only invasive pests, but also a pest for cruciferous vegetables such as cabbage, kale, broccoli, mustard greens, and others, earning them the name "harlequin cabbage bugs". If left unchecked, this pest can cause entire crops to wither and die.

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Overview of the harlequin beetle

Harlequin beetle nymphs look a little different from the adults. Source: goingslo

Harlequin beetles have a distinctive look with their black, shield-shaped bodies speckled with yellow, orange, and red patterns. This aposematic coloring is a form of self-defense to deter predators. They are approximately 8-11.5 mm (3/8 in) long, and the female beetles are slightly larger than the males. It is no surprise that this beetle stimulates the imagination of many people who have come up with a variety of names for it, such as the “cold beetle”, the “fire beetle” and “turtle back”.

Life cycle of harlequin bugs

Harlequin beetles are destructive pests because, under favorable conditions, they can develop up to three generations per year. A generation or life cycle of harlequin beetles develops over 50-80 days as they go through the egg, nymph, and adult stages.

These beetles overwinter as adults and hatch in early spring each year. Adult females mate and lay about a dozen black and white eggs per female on the underside of the leaves. The eggs have a very recognizable barrel shape at their end, which is characterized by two rows of alternating black and white stripes and a black dot. Depending on the temperature, the eggs hatch into nymphs 4 to 29 days later.

Harlequin beetle nymphs usually go through 5 or 6 stages and become lighter in color with each progressive moult. A newly hatched harlequin beetle nymph cannot fly, but it does develop its wings in the final instar.

Common living spaces

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 winter hosts. Harlequin beetles are not well adapted to cold winter temperatures, which is why they are more common a pest in the southern United States. Their population can be particularly noticeable after mild winters. As soon as the weather warms up in early spring, full-grown harlequin beetles appear and can be found on the leaves of various host plants. Eggs are located on the underside of the leaf surfaces. The eggs are easy to spot, black and white striped and cylindrical in shape, and they are very easy to spot as harlequin beetle eggs on your plants.

What do harlequin beetles eat?

The harlequin bug (Murgantia histrionica Hahn) feeds on over 50 plant species, but strongly prefers host plants of the cabbage family, which is why they are also known as harlequin cabbage bug. Both adults and nymphs feed on plant tissue with their piercing and sucking mouthparts. The damage to the leaves looks like light, cloudy, or brown patches of dead plant tissue.

A large-scale infestation with harlequin cabbage bugs leads to large-scale wilting of the leaves and inhibits the overall development of the plant. Whole plants can suffer or lose market value if they cannot recover from an infestation. A harlequin beetle can 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 beetles

Harlequin beetle nymphA good look at a harlequin beetle nymph. Source: Judy Gallagher

While these stink bug relatives are beautiful to look at, they can do serious harm 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 control method so as not to harm beneficial insects in your garden.

Organic or chemical control

Although the harlequin beetle is a noxious pest, its adults, nymphs, and eggs can all be easily spotted and destroyed. Check your plants frequently during the growing season, hand-picking adult harlequin beetles and dropping them in a cup of soapy water to kill them. Look under the leaves of the host plants and mash any harlequin beetle eggs you can find there. Hand-picking or even vacuuming bugs can be an effective way to keep harlequin beetles under control.

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

Some pyrethrin formations are approved for biological use. Use pyrethrin at the beginning of the season and schedule it to use it every couple of weeks. Follow the directions on the package carefully as pyrethrin is a broad spectrum insecticide.

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

Environmental control

Harlequin beetles have relatively few natural enemies due to their self-defense mechanisms due to their pungent smells and bright colors. There are three different species of native Hymenoptera wasps that parasitize harlequin bugs' eggs: Ooencyrtus johnsoni Howard, Trissolcus murgantiae Ashmead, and Telenomus podisi Ashmead. T. murgantiae was released in California as a form of biological control, and researchers have also found harlequin beetle eggs parasitized in Virginia.

One environmental control method for harlequin beetles is to grow a few trap crops, such as fast-ripening mustard fruits, near the planned main harvest at the start of the season. Trap cultures can help you identify and kill the first wave of adults to mitigate a large infestation later, as harlequin beetles use pheromones to congregate on the best source of food. Alternate trap cultures with a non-host crop phase to further reduce the overall population of this pest.

Prevent harlequin bugs

A great way to control this pest is to deprive the harlequin beetle of any ability to survive the winter. This means that plant debris and residues from plants such as kale or mustard are removed immediately after the harvest. Removing annual weeds from around susceptible plants is another way to prevent adult harlequin beetles from wintering near them.

As the weather warms up, add floating row covers around the plants to create a physical barrier against harlequin beetles. If you are already using floating row covers to prevent cabbage moths from landing on your cabbage moths, you are already well equipped to prevent or control harlequin beetles as well. These covers prevent the sucking damage that occurs when a harlequin beetle goes to feed; They never reach the plant and therefore cannot cause yellow or brown spots and leaf damage that appear on the leaves.

frequently asked Questions

Adult harlequin beetleAn adult harlequin beetle. Source: K Schneider

Q: Are harlequin beetles harmful?

A: Yes, harlequin beetles are a widespread pest in the southern United States, and they particularly harm cruciferous vegetables such as cabbage, kale, mustard, etc. These relatives of stink bugs are very common pests.

Q: Which spray kills harlequin beetles?

A: Pyrethrin is a broad spectrum insecticide that, on contact, can kill a wide variety of insects, including harlequin beetles. It disrupts insects' nervous systems, 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 beetle's life cycle

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