Bright splashes of crimson, orange, and black decorate the harlequin bug, making this insect appear playful. However, don’t let the colorful markings fool you. Harlequin bugs can quickly become a gardener's worst nightmare. As piercing-sucking insects, they extract nutrients and moisture from plants. Left unchecked, entire crops can be decimated.

While harlequin bugs prefer brassica crops, they will also attack beans, corn, tomatoes, and more when their first choices are not available. Learning how to identify harlequin bugs, their life cycle, and organic control methods is key to protecting your garden from devastation.

What Are Harlequin Bugs?

Harlequin bugs (Murgantia histrionica) are stink bugs measuring about 3/8 inch (1 cm) in length. They earned the name “stink bug” due to the foul odor they emit when threatened. This defense mechanism deters some predators. Their striking color pattern of black, red, orange, and yellow separates harlequin bugs from other stink bugs which are typically plain brown, green, or gray.

These insects use piercing-sucking mouthparts to feed on plant juices. Preferred host plants include:

• Cabbage
• Broccoli
• Cauliflower
• Brussels sprouts
• Kale
• Collard greens
• Mustard
• Turnips
• Radishes

When populations are high or preferred brassicas are unavailable, harlequin bugs will also drink from squash, beans, corn, asparagus, okra, and tomato plants.

Feeding damage appears as light dots on stems and leaves. These tiny spots surround the puncture hole from the harlequin bug’s beak. With continued feeding, the dots grow into irregular bleached areas. Leaves turn crisp and dry out. Heavily damaged leaves drop early.

Entire young seedlings rapidly collapse under harlequin bug pressure. Growth in older plants slows as resources are extracted. Wilting, stunting, and plant death will occur if harlequin bugs are left uncontrolled.

On fruiting crops like tomatoes, hollowed out lesions surround feeding sites. Damaged areas turn brown or black and remain hard and sunken as the fruit matures. Squash and beans develop whitish bumps, pits, and scars where harlequin bugs fed.

Life Cycle of Harlequin Bugs

Getting harlequin bugs under control requires diligence and excellent timing. It’s critical to understand their life cycle and habits.

Overwintering

Adults seek sheltered spots to overwinter, tucked under plant debris, leaf litter, rocks, and mulch. They become active again in spring after several weeks of warm weather. Harlequin bugs cannot survive harsh winters in areas with sustained below freezing temperatures.

Spring Emergence

Overwintered adults emerge hungry in early spring. After two weeks of feeding, females start laying eggs.

Egg Laying

Females lay 10-15 eggs at a time, arranging them neatly in a double row. The black and white barrel-shaped eggs resemble a miniature circus tent. They are glued upright, directly onto the host plant.

In cooler spring temperatures, eggs may take up to 20 days to hatch. As conditions warm, incubation shortens to as little as 4 days. Females can produce several clutches totaling 100-200 eggs over a season.

Nymph Stage

Tiny black and red nymphs emerge from the eggs. Initially round in shape, they lack wings. Nymphs molt 5 times over 4-6 weeks as they grow. With each successive molt, their markings become more distinct until reaching the adult pattern.

Young nymphs tend to cluster and feed close to where they hatched. As they disperse, feeding damage spreads across more leaves.

Adulthood

After their final molt, nymphs become reproductive adults. Females soon start laying eggs, beginning the cycle again.

Generations Per Year

In warm climates, harlequin bugs produce up to 4 generations per year. Cooler regions may only support 1-2 generations. The last generation of the season survives winter as adults.

Their fast reproduction coupled with mobility and wide host range allow harlequin bug populations to explode over a single growing season. Diligence is required to prevent them from getting out of control.

Organic Ways to Control Harlequin Bugs

Stop harlequin bugs from sucking the life out of your garden using these organic techniques:

Remove Plant Debris

Eliminate shelters where adults seek refuge over winter. After harvest, pull spent plants and till the garden to chop and bury debris. Dispose of heavily infested plant waste in sealed bags, rather than the compost pile.

Field edges and ditches near the garden also serve as winter hideouts. Mow down weeds and grasses to disrupt overwintering sites.

Handpick Adults

Start searching for harlequin bugs as soon as temperatures warm in spring. Inspect the undersides of leaves where they often gather. Handpick any adults found and drop them into a bucket of soapy water. Repeat this search and destroy mission regularly.

Destroy Eggs

Check plants closely for harlequin bug eggs beginning in early summer. Scrape off any egg clusters detected using a butter knife or your fingernail. Drop the eggs into soapy water to kill them. Crushing eggs is also effective.

Apply Insecticidal Soap

After eggs appear, watch for newly hatched nymphs clustered near the empty shells. Insecticidal soap sprayed directly on young nymphs will smother and kill them. Repeat applications 7-10 days apart to control subsequent hatches.

The soap spray must contact nymphs to work. Thorough coverage of undersides of leaves improves results. Spray in early morning or evening when pollinators are less active.

Insecticidal soap loses effectiveness on larger, more mature nymphs. It also may burn leaves if applied during hot, sunny weather above 85°F.

Use Spinosad

As a last resort for heavy infestations, apply spinosad according to label instructions. Spinosad is a natural bacterium that disrupts the insect digestive system, leading to death in 1-2 days. It is approved for organic gardening when cultural methods fail to provide adequate control.

Spinosad works better on harlequin bug adults than insecticidal soap. However, it is also toxic to beneficial insects. Use strategically rather than broadcasting across your entire garden. Reapply 7-10 days later if needed.

Row Covers

Prevent access to plants by covering them with row cover fabric. Drape the lightweight material directly over crops and bury the edges. Leave plenty of slack so the growing plants can push up the fabric.

Install row covers at planting time before harlequin bugs take up residence. Keep covered until harvest. No insects can penetrate the barrier, but water and light pass through. This is an ideal solution for brassicas that don’t require pollination.

Invite Predators

Harlequin bugs do have natural enemies. Attract beneficial predators by providing habitat around your garden.

• Plant small flowering plants and herbs. They supply pollen and nectar food sources for parasitic wasps and flies.
• Include shrubs and permanent plantings. These provide shelter for spiders, praying mantises, and ground beetles that eat harlequin bugs.
• Create brush piles. Birds nest and hunt insect prey in these areas.
• Avoid broad spectrum insecticides. These products kill predators and pests alike.

With an inviting habitat, nature will provide free pest control for you.

Use Trap Crops

Take advantage of the harlequin bug’s appetite for certain plants. Bait them away from your primary crops.

Plant a perimeter of mustard greens, arugula, radish, or other favorite host plants. As migrating adults arrive in spring, they will congregate heavily on these sacrificial plants. Monitor the traps closely. Before harlequin bugs disperse into the main garden, pull up the infested traps, seal in bags, and destroy them.

You can also plant small patches of trap crops throughout the garden near susceptible crops. They draw nearby harlequin bugs away like magnets.

Conclusion

Harlequin bugs are a challenging pest due to their mobility, high reproduction rate, and wide host range. However, their life cycle also offers opportunities for control. Follow cultural practices to prevent infestations from ever taking hold. Monitor carefully and use targeted organic treatments at key life stages. With a diligent integrated pest management plan, you can enjoy a harlequin-free garden.