Harlequin Bug

The harlequin bug is a brightly colored insect known for its distinct black and red patterns. However, it can be a serious pest for many garden plants, making early detection and control crucial for plant protection.

Host Plants

Harlequin bugs have a broad host range but are particularly problematic on crops in the Brassicaceae family, which includes many popular vegetables like cabbage, broccoli, Brussels sprouts, radishes, and kale. They can also feed on a variety of other plants, including squash, beans, tomatoes, and corn, among others. Certain flowers and weeds, such as sunflowers and cleome, are also known hosts.

Regions impacted

The Harlequin bug is native to Mexico and Central America but has expanded its range and is now found throughout the United States. It prefers warmer climates and is more common in southern states, but it has been found as far north as New Jersey and Illinois. It’s also common in parts of South America and has been introduced to Australia and New Zealand.

Description

The Harlequin Bug, or Murgantia histrionica, is a brightly colored stink bug known for the distinctive harlequin pattern on its back, usually black with vibrant orange, red, or yellow markings. Adult bugs are approximately ⅜ inch long and ¼ inch wide. Nymphs (immature bugs) are smaller and vary in coloration, ranging from red and black to green or yellow with black bands, becoming darker as they mature.

Life Cycle

The life cycle of a harlequin bug consists of three main stages: egg, nymph, and adult. It undergoes an incomplete metamorphosis process, also known as hemimetabolism, which does not include a pupal stage like in complete metamorphosis found in butterflies or beetles.

Egg Stage: The life cycle begins when a female harlequin bug deposits her eggs on the underside of host plant leaves or stems. The eggs are barrel-shaped and white with two distinct black bands at the top. These eggs are typically arranged in double-row clusters. Depending on the temperature, the eggs hatch in about 4-15 days.

Nymph Stage: The hatchlings, known as nymphs, are wingless and exhibit a bright coloration that can vary from red and black to green or yellow with black bands. As they mature, they become darker. The nymphs undergo five instar stages, each one slightly larger and darker than the previous. The transition from one instar to the next involves a shedding of the skin, known as molting. This nymphal stage lasts about a month.

Adult Stage: After the final molt, the nymph becomes an adult. Adult harlequin bugs are approximately 3/8 inch long and are distinctively colorful, with black and vibrant orange, red, or yellow markings. Once mature, females can mate and lay eggs, starting the cycle again.

In warmer climates, harlequin bugs can produce multiple generations per year, leading to a continuous presence of bugs at different stages of the life cycle. Overwintering happens generally in the adult stage, where they find shelter in crop debris or other protected areas to survive the cold weather.

Damage and Detection

Damage

Both the nymphs and adults feed on the plant sap by piercing the plant tissues and sucking out the juices. This feeding leads to stunted growth, wilting, and eventual death of the plant (if the infestation is heavy). The damage appears as white or yellow blotches, or stippling, on the leaves, buds, and seed pods of the host plants. In severe cases, whole patches of plants can be killed.

In commercial crop production, significant yield loss can occur, making harlequin bugs a serious pest for farmers. They can also be problematic in home gardens, particularly where cruciferous vegetables are grown.

Detection

Detecting harlequin bugs involves inspecting the plants for both the bugs themselves and the symptoms of their feeding. The distinctive coloring of the adult bugs and the nymphs make them quite noticeable. The eggs, laid in neat double-row clusters on the undersides of leaves or on stems, are also quite visible to the naked eye.

Other signs of infestation include the wilting and yellowing of plants, as well as the presence of the distinctive blotches or stippling on leaves caused by bug feeding. Regular and careful inspection of plants is the best way to detect an infestation early and take appropriate action.

Given their bright colors and distinctive patterns, harlequin bugs are not difficult to spot when you know what to look for. However, they can move quite quickly and may drop to the ground and hide when disturbed, so careful observation is necessary. Always remember to check the underside of leaves and around the base of plants, as these are favorite spots for these pests.

Prevention and Control

Preventing and controlling harlequin bug infestations can be challenging but is crucial for maintaining healthy and productive crops or gardens. Here are several strategies that can be used:

Cultural Controls

• Crop Rotation: Changing the types of crops planted in a specific area from year to year can help break the life cycle of the harlequin bug, reducing their populations.
• Sanitation: Remove and destroy crop residue after harvest, as well as any weeds or other non-crop plants that may serve as a food source or shelter for harlequin bugs.
• Plant Trap Crops: Certain plants, like mustard or radish, attract harlequin bugs and can be used to draw them away from your main crop. For example, radishes are said to repel harlequin bugs and can be planted as a “trap crop” – the bugs are drawn to the radishes, leaving your other plants alone. Once the bugs are concentrated on the trap crop, it can be treated with an insecticide or removed and destroyed.
• Companion Planting: This method involves planting certain types of plants together to deter pests.  Strong-smelling plants like garlic, onions, and chives may deter the bugs. However, the effectiveness of companion planting can be variable and might not be the sole solution for a serious infestation.

Biological Controls

• Birds: Birds can also be effective predators of harlequin bugs. Providing bird-friendly habitat in or near your garden can help attract these helpful creatures.
• Egg Predators: Various egg predators, such as minute pirate bugs, lacewings, and predatory bugs, consume harlequin bug eggs. Additionally, some parasitoid wasps in the Encyrtidae and Scelionidae families parasitize the eggs, proving to be effective natural enemies.

Chemical Controls

• Insecticidal Soaps: Insecticidal soaps can kill harlequin bugs on contact. These products are less toxic than many other insecticides and are generally safe to use on food crops. However, they may need to be applied more frequently to maintain control.
• Diatomaceous Earth: Diatomaceous earth (DE) is a non-toxic pesticide that can be used to control harlequin bugs. It is made from the fossilized remains of tiny aquatic organisms known as diatoms. The microscopic sharp edges of DE can cut through the bug’s exoskeleton, causing it to dehydrate and die. Sprinkle DE around the base of your plants and on the leaves, both top and bottom, where the bugs congregate. This method can be effective, but DE needs to be reapplied after rainfall or irrigation, as it is ineffective when wet.
• Neem Oil: Neem oil is a natural pesticide derived from the seeds of the neem tree. It can be used to manage various pests, including the harlequin bug. It works by disrupting the life cycle of the bugs and preventing them from eating or growing. Apply it directly onto the bugs and plants showing signs of infestation. Be sure to follow the instructions on the bottle for best results. Note that neem oil can also harm beneficial insects, so use it judiciously.
• Insecticides: Various insecticides can be effective against harlequin bugs. Choose products labeled for use against this pest, and always follow label directions. Because these bugs have a hard shell, you may need to use a product with a stronger active ingredient or a surfactant to help the product stick to and penetrate the bug’s body.

Mechanical Controls

• Hand-Picking: If populations are low, hand-picking can be an effective control method. Harlequin bugs can be removed from plants and dropped into a bucket of soapy water to kill them.
• Row Covers: Lightweight fabric row covers can be used to physically prevent harlequin bugs from reaching plants. Covers should be put in place after planting and removed during flowering if the plants require pollination.

Prevention and control of harlequin bugs require diligence and a multi-pronged approach. By combining several of the strategies listed above, you can help protect your plants from this damaging pest. Remember to monitor your plants regularly for signs of infestation and take action at the first sign of trouble.