The harlequin bug (Murgantia histrionica), also known as calico bug, fire bug or harlequin cabbage bug is a black stinkbug that is particularly destructive to cabbage and related plants in tropical America as well as throughout most of North America, especially the warmer parts of United States.
In addition to cabbage, harlequin bugs can be a major pest of broccoli, radishes, kale, collards, mustard, turnips, Brussels sprouts and cauliflower. They may also attack corn, tomatoes, okra, squash, asparagus and beans.
Both adults and nymphs cause damage to stems, leaves, fruits and seeds. They use their piercing mouthparts to inflict damage and suck away plant sap. Damage on leaves and stem look like uneven discolored spots. Young plants if left unchecked, will wilt, turn brown and eventually die. Mature plants will have their growth stunted. Damage on fruits will appear as dark holes or white-yellowish spots.
Symptoms include cloudy areas around the point of extraction, browning and wilting plants, and slower plant growth.
Adult harlequin bugs are attractive shield-shaped shiny black insects with bright red, yellow or orange markings. They measure about 7-10 mm in length.
Eggs are light colored barrel-shaped, 1 mm long and are laid in clusters in the foliage. Eggs hatch in 5-14 days.
The nymph is oval and similar to adults in appearance and color but slightly smaller and lack wings. Nymphs mature into adults in 5-8 weeks.
Generally 1-3 generations depending on location with warmer places more likely to have more generations.
Organic Control and Prevention of Harlequin Bugs:
1. Grow resistant varieties: Some types of brassica plants are naturally resistant to Harlequin bugs. The following varieties are recommended:
Cabbage: Copenhagen Market 86, Headstart, Savoy Perfect Drumhead, Stein’s Flat Dutch, Early Jersey Wakefield.
Collards: Green Glaze.
Cauliflower: Early Snowball X, Snowball Y.
Radishes: Red Devil, White Icicle, Globemaster, Cherry Belle, Champion, Red Prince.
2. Cultural control: Destroy heavily weeded and bushy areas in and near your garden. Adult stink bugs prefer overwintering in such sites among legumes, blackberries, Russian thistle, mustards and little mallow. Till the growing area, destroy and rid of crop debris and good weed management will help minimize stink bug populations.
3. Monitor and handpick: Harlequin bugs have decent mobility so be prepared. They also release a stink gas when threatened so beware and cover your nose! Remove them and drop them into a bucket of soapy water. Shaking infested plant or tree will send them tumbling down. Growers have successfully controlled harlequin bugs by frequent vacuuming. Spray plants with water to knock them down and kill them off.
4. Plant trap crops: Mustard, millet, buckwheat, sorghum, sunflower, marigolds, lavender and chrysanthemums are good trap crops to attract stink bugs to attack them rather than your crop of interest. Once these trap crops are infested, keep a bag ready to trash the infested plant in.
5. Physical traps: Yellow sticky traps or bucket painted yellow filled with soapy water can rid of quite a few unsuspecting stink bugs. An open pipe painted yellow stuck into the ground can also be used effectively for trapping stink bugs. Then there are commercially available stink bug traps that can be tried out.
6. Beneficial insects include ants, ladybird beetles, minute pirate bugs and some lacewings, all of which destroy stink bug egg masses. Attract these insects by planting several nectar producing flowers. Praying mantises, toads and some birds (including chickens and ducks) would love to feed on some adult Harlequin bugs.
7. Sprinkle diatomaceous earth in your garden and in prone areas. It works by breaking down the waxy protective layer on the stink bugs exoskeleton, eventually causing it to dehydrate.
8. Make a garlic spray and use as frequently as needed. Stink bugs detest the potent smell of garlic and will repel them from your garden.
9. Kaolin, a soft, white silicate clay mineral can be combined with water to form a protective physical powdery barrier that will prevent stink bugs and other pests from feeding on plant tissue.
10. Use an organic insecticidal soap and spray this solution directly on stink bugs or in areas they frequent. The soap kills the bugs by breaking down their protective exterior and dehydrating them.
11. Neem oil is another natural product that can help reduce stink bug populations by disrupting their feeding and mating habits.
12. Companion planting: Plant garlic, tansy, mint, catnip and radish to help repel Harlequin bugs.