Murgantia histrionica Hahn Hemiptera Pentatomidae

Natural History

Distribution. A native of Mexico and Central America, harlequin bug was first observed in the United States in Texas, in 1864. Its appearance, coinciding with the occurrence of Union troops during the American Civil War, earned it the name "Sherman-bug" and "Lincolnite" in parts of the south. It rapidly spread throughout the southern states, and eventually reached northern locales such as Colorado, Iowa, southern Michigan, Pennsylvania, and Massachusetts. It is considered to be a serious pest only in southern states, however, and is not regarded as a problem in California. Harlequin bug is also a pest in Hawaii.

Host Plants. Harlequin bug is principally a pest of crucifers, attacking asparagus, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, col-lards, kale, kohlrabi, mustard, radish, rutabaga, turnip, and watercress. This bug is reported to be especially fond of horseradish. In the southernmost states, crucifers do not thrive during the summer months, and the bugs are forced onto other plants. Thus, they are sometimes found feeding on beans, okra, squash, tomato and many other vegetables, but this is usually due to lack of normal food. Harlequin bug feeds readily on cruciferous weeds such as wild mustard, Bras-sica spp.; shepherds purse, Capsella bursa-pastoris; and pepperweed, Lepidium spp.; and related mustard oil-containing plants such as members of the family Capparaceae. Other weeds common in crops, such as pigweed, Amaranthus spp.; and lambsquarter, Cheno-podium album; are also fed upon, and reproduction occurs on these plants.

Natural Enemies. Harlequin bug appears to be relatively free of natural enemies, other than for egg parasites and general predators. The egg parasitoids are Oencyryus johnsoni (Howard) (Hymenoptera: Encyrtidae), Trissolcus murgantiae Ashmead, and T. podisi Ashmead (both Hymenoptera: Scelionidae). The best known species is O. johnsoni, which is reported frequently from harlequin bug eggs, and caused up to 50% mortality during a harlequin bug outbreak in Virginia (White and Brannon, 1939). This parasite is widely distributed, and apparently has other hosts. It attacks eggs in all stages of embryonic development, and prevents them from hatching (Maple, 1937). However, O. johnsoni is not the only effective parasite, as T. murgantiae was observed to parasitize 45% of harlequin bug eggs in North Carolina, at locations where O. johnsoni parasitized only 30% of eggs (Huffaker, 1941). Because of its effectiveness, T. murgantiae was introduced into California (DeBach, 1942).

Life Cycle and Description. Harlequin bug breeds continuously in the southern portions of its range. During mild winters all stages have been observed as far north as Virginia. In colder climates, only the adults survive the winter in sheltered locations. They seek shelter in and near fields, among overwintering crop plants, and in other organic debris such as dead leaves and bunches of grass. Two or three generations per year seems normal, but Paddock (1915a) indicated four generations in south Texas.

  1. The adults begin depositing eggs about two weeks after becoming active in the spring. Eggs are deposited beneath leaves, usually in clusters of 12 arranged in two rows of six, at intervals of 5-6 days. As the female nears the end of her life, the egg batches get slightly smaller and the arrangement less regular. The eggs are barrel-shaped, and measure about 1.301.38 mm long and 0.90-0.92 mm in diameter. They are light gray or pale yellow, and generally are circled by two black bands. They may also bear small black dots or spots, and the top has a semicircular black marking. The average number of eggs is reported to be 115 per female. Egg deposition may occur over a period of about 40-80 days. Eggs hatch in about 4-5 days during warm weather, while 15-20 days may be required during cool weather.
  2. Upon hatching, young nymphs stay clustered near the old eggs for 1-2 days. The newly hatched nymphs are pale green with black markings, but soon become brightly colored—black or blue, with
Eggs Hellula Undalis
Harlequin bug eggs on foliage.

red and yellow or orange markings. Paddock (1918) indicated that there were six instars in Texas, and that nymphal development could be completed in just 30 days. He gave average development times as 3.4, 3.2, 4.7, 4.7, 7.0, and 4.3 days, respectively, for the six instars developing under summer conditions. Under spring conditions, development times were increased by about 30%. In contrast, White and Brannon (1939) reported five instars and a development time requirement of about 40-60 days during the summer, and slightly longer, perhaps 70 days, during cool weather.

Adult. The adults usually live about 60 days, but may live considerably longer during the winter. They measure about 8.0-11.5 mm long. The adults are brightly colored, similar to the large nymphs, principally black and yellow or black and red. The color pattern varies, with the spring and summer bugs more brightly colored than the overwintering insects. As with many stink bugs, harlequin bugs produce a disagreeable odor if disturbed, and birds avoid eating them. (See color figure 143.)

The biology of harlequin bug was provided by Chit-tenden (1908b), Paddock (1918), and White and Bran-non (1939). A key to distinguish stink bugs commonly affecting vegetables is found in Appendix A.

Damage

The piercing-sucking feeding behavior of this insect results in white blotches at the site of feeding. Wilting, deformity, and plant death may occur if insects are abundant. Mild winters are said to favor survival and subsequent damage (Walker and Anderson, 1933). Once considered the most serious crucifer pest in the south, this insect has been relegated to minor status in commercial production and persists mostly as a home garden pest.

Management

Chemical Control. Insecticides are applied to the foliage for suppression of this bug. Harlequin bug can be difficult to control with insecticides; targeting the young bugs and thorough coverage are recommended (Rogers and Howell, 1973). Soap applied alone or in

Hemiptera Brocoli
Harlequin bug nymph.
Adult harlequin bug.

combination with rotenone provided good control (Walker and Anderson, 1933; 1934).

Cultural Practices. Trap crops, usually consisting of early-planted mustard, rape, or kale are sometimes recommended to divert the overwintering bugs from the principal crop. Such trap crops must be sprayed or destroyed, however, or the adults will soon move to the main crop. Destruction of crop residues, on which the insect may overwinter in the north or oversummer in the south, is an important cultural practice to alleviate harlequin bug damage.

Host-Plant Resistance. Sullivan and Brett (1974) studied the relative susceptibility of different crucifer crops to harlequin bug in North Carolina. They reported that mustard and Chinese cabbage were the most susceptible; turnip, kale, rutabaga, and some radishes were intermediate; and cauliflower, cabbage, broccoli, collards, Brussels sprouts, kohlrabi, and most radish varieties were fairly resistant. Cabbages were the most resistant crop, but considerable variation among cultivars was evident.

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