Euschistus variolarius Palisot de Beauvois Hemiptera Pentatomidae

Natural History

Distribution. Onespotted stink bug is native to North America. It is distributed widely; in the United

States it is absent only from the southwestern states. In the midwest and other northern areas it is considered to be the most common stinkbug species (Esselbaugh, 1948). In Canada it is known from Quebec and Ontario west to British Columbia.

Host Plants. This species is reported to feed on numerous plants. Among vegetable crops attacked are asparagus, bean, cantaloupe, corn, cowpea, mustard, onion, pea, potato, squash, and tomato. Field crops that serve as hosts are alfalfa, clover, cotton, oats, rye, sugarbeet, timothy, tobacco, and wheat. Such fruit crops as gooseberry, grape, peach, pear, and raspberry were damaged. Some of the numerous weeds known to support this species are burdock, Arctium sp.; curly dock, Rumex sp.; goldenrod, Solidago sp.; horseweed, Erigeron canadensis; milkweed, Asclepias sp.; mullein, Verbascum thapsus; pigweed, Amaranthus sp.; ragweed, Ambrosia sp.; and thistle, Cirsium sp. Trees are commonly reported as hosts; among them are black walnut, elm, pine, poplar, sassafras, tulip tree, and willow.

Natural Enemies. Onespotted stink bug is parasitized by Telenomus and Trissolcus spp. (Hymenoptera: Scelionidae) and several flies, including Gymnosoma fuliginosum Robineau-Desvoidy, Trichopoda pennipes (Fabricius), Cylindromyia binotata (Bigot), C. fumipennis (Bigot), Gymnoclytia occidua (Walker), Cistogaster immaculata Macquart, and Euthera tentatrix Loew (all Diptera: Tachinidae) (McPherson, 1982).

Yeargan (1979) studied mortality of brown stink bug eggs in Kentucky, and reported that when egg masses were distributed in crops, about 50% were parasitized,13% were destroyed by predators, and 25% failed to hatch probably due to undetectable natural enemy feeding. When stink bugs were allowed to oviposit naturally on plants 71% were parasitized, 26% were destroyed by predators, and 1% failed to hatch. Natural enemies clearly have the potential to destroy a high proportion of stink bug eggs.

Life Cycle and Description. There is only a single generation per year throughout the range of this species. The eggs are deposited in late April to June, with adults produced by August. The adults overwinter, and both new and overwintering adults can be found late in the summer.

  1. The eggs are barrel-shaped, and attached on end to the underside of a leaf. The upper end of the egg is ringed with a single row of 27-33 small spines. Initially, the eggs are light green, but soon turn creamy white. They measure about 1.1 mm long and 0.9 mm wide. Females deposit the eggs in clusters; the average number per cluster is about 14. The incubation period of eggs is about six days (range 3-10 days).
  2. There are five instars. The mean length (range) was reported by Munyaneza and McPherson (1994) to be 6 (6), 11 (9-14), 10 (8-12), 12.6 (7-15), and 10.6 (8-17) days, respectively. Esselbaugh (1948) reported mean (range) development times of 3.5 (211), 7.5 (4-16), 7.9 (5-17), 7.7 (5-13), and 10.0 (8-16), respectively. The first instars are grayish-brown on the thorax, the abdomen similar but lighter and marked with red. First instars measure about 1.5 mm long. Second instars are whitish, and conspicuously marked with black spots on the head and thorax and red on the abdomen. They measure about 2.8 mm long. Third instars are similar to second instars in appearance, except that the abdomen is greenish and they measure about 4.1 mm long. Fourth instars are greenish, with a row of red spots along the median line of the abdomen. The wing pads are evident in this instar, which measures about 6.7 mm long. The fifth instar has a dark yellow head and thorax, and a green abdomen. The wing pads are well-developed, overlapping the first three abdominal segments. This instar measures about 10.3 mm long. The nymphal instars of E. variolaris are very similar to those of brown stink bug, E. servus (Say).
  3. The adult bugs are grayish-brown. They measure 11.0-15.0 mm long. The lateral edges of the pronotum, or "shoulders," generally taper to a sharp point. In males of this species the ventral surface of the tip of the abdomen is marked with a single dark spot, which serves as the basis for the common name. Because it is sex-specific, it is not a particularly useful diagnostic character. The adults overwinter under dry leaves and other plant debris, under logs, and beneath mullein leaves. Winter mortality is high, with 80% or more of the population perishing. Bugs begin mating a few days after emerging from diapause in the spring. The average time from copulation to egg laying is 27 days.

The biology and description of the nymphs were given by Parish (1934) and Munyaneza and McPher-son (1994). The latter authors also gave information on rearing, and characters to distinguish onespotted stink bug nymphs from brown stink bug nymphs. A key to distinguish stink bugs commonly affecting vegetables is also found in Appendix A.

Damage

Nymphs and adults feed on tender shoot tissue, buds, and fruit. Most damage to vegetables takes the form of deformed fruit, aborted blossoms, or death of young tissue. Annan and Bergman (1988), Sedlacek and Townsend (1988), and Apriyanto et al, (1989a,b)

Euschistus Pronotum
Adult onespotted stink bug.

found that young corn plants were damaged by stink bug feeding. Symptoms included are chlorotic lesions, tightly rolled leaves, wilting, stunting, increased tillering, delayed silk production, and smaller grain weight. Even a single day of feeding by stink bugs reduced corn growth and yield. The first instars, however, feed a little or not at all—a common condition among stink bugs.

Management

Phillips and Howell (1980) stressed the importance of weeds in stink bug biology, and noted that damage was higher in weedy areas, especially following senescence of the weeds. Reduced tillage practices and presence of cover crops, especially wheat, contributed to increase in stink bug abundance. Foliar insecticides are effective, with special care needed to protect the blossoms and fruit.

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