Chlorochroa uhleri Stl Hemiptera Pentatomidae

Natural History

Distribution. These stink bugs are native to western North America. Say stink bug is found throughout the west, from Montana and eastern Texas west to Caifornia and British Columbia. It has also been taken in Arkansas, which seems to be unusually far east for this species. Similarly, Uhler stink bug is found from the Saskatchewan and the Dakotas, Nebraska and New Mexico west to the Pacific Ocean.

Host Plants. Say and Uhler stink bugs feed on the fruit and seeds of many plants. They are known principally as a pest of grains, and prefer to attack the seed head of such crops as alfalfa, barley, oat, rye, and wheat. However, on occasion they damage such vegetables as asparagus, bean, cabbage, lettuce, pea, and tomato. They also feed extensively on such weeds as broom snakeweed, Gutierrezia spp.; lambsquarters, Chenopodium album; mallow, Malva spp.; musk thistle, Carduus nutans; pigweed, Amaranthus spp.; prickly pear cactus, Opuntia sp.; Russian thistle, Salsola kali; tansymustard, Descurainia pinnata; toadflax, Linaria vulgaris; tumblemustard, Sisymbrium attissimum; sage, Artemisia spp; saltbush, Atriplex spp.; and feathergrass, Stipa spp.

Natural Enemies. Several parasitoids are known. An egg parasitoid, Telenomus utahensis Ashmead (Hymenoptera: Scelionidae), is an important mortality factor of Say stink bug, sometimes causing 60% mortality or greater late in the season (Jubb and Watson, 1971a,b). When this wasp discovers an egg clutch, few if any eggs escape parasitism. Several generations of the parasitoid occur annually (Caffrey and Barber, 1919). The other known wasp parasitoids, Telenomus podisi Ashmead (Hymenoptera: Scelionidae) and Ooencyrtus johnsoni (Howard) (Hymenoptera: Encyrti-dae), also attack eggs. Among fly species reared from Say stink bug are Cylinromyia armata Aldrich, C. euche-nor (Walker), and Gymnosoma fuliginosum Robineau-Desvoidy (all Diptera: Tachinidae). Although the Cylinromyia spp. seem to be of little importance, the latter fly species attacks up to 25% of late instar nymphs and adults. Parasitoids of Uhler stink bug are less well-known, though Telenomus utahensis caused higher levels of parasitism in Uhler stink bug than in Say stink bug (Jubb and Watson, 1971b), and G. fuliginosum is also known from C. uhleri.

General predators, including the assassin bug Sinea spinipes (F.) (Hemiptera: Reduviidae), and the ambush bug, Phymata erosa Stal (Hemiptera: Phymatidae), feed on nymphs. The soft-winged flower beetle, Collops bipunctatus Say (Coleoptera: Melyridae), feeds on stink bug eggs. Songbirds and lizards sometimes consume both Say stink bug and Uhler stink bug (Knowlton, 1944; Knowlton et al., 1946) despite the fact that some vertebrate predators learn to avoid these odor-producing and presumably distasteful insects.

Life Cycle and Description. Three or four generations of Say stink bug are known from New Mexico. The overwintering adults deposit eggs in late April or May, with first generation adults appearing in June, second in August, and third in September. A small fourth generation sometimes occurs, though many nymphs from this generation perish with the onset of cold weather. The adults from generations 2-4 enter diapause during late October or early November, and re-emerge the following spring. A complete generation requires about 80 days. Uhler stink bug's biology and morphology are largely undescribed, but presumably about the same as Say stink bug.

  1. The eggs of Say stink bug are barrel-shaped, and deposited on end. The height is 1.1-1.2 mm, and diameter about 0.6-0.9 mm. When viewed from above, the egg is marked with three white circles which alternate with gray. On one side of each egg is an irregular patch of gray. Mean duration of the egg stage is about nine days (range 4-13 days), though during the warmest months egg hatch tends to occur in 5-7 days. Eggs darken in color immediately preceding hatch. Egg clusters are placed on the underside of some object. Overwintering adults may deposit eggs on the dead plants or rubbish comprising their overwintering quarters, but later generations tend to oviposit on green plants. They often are placed in parallel rows, usually two or four rows, with rows consisting of 720 eggs. This tendency is most pronounced when ovi-position occurs on the narrow stems of grasses which constrain oviposition, whereas on broad surfaces the eggs may consist of several rows. The number of eggs per cluster averages about 26 (range 13-43 eggs).
  2. There are five instars in Say stink bug; the mean (range) duration is 5.0 (5), 8.2 (7-9), 6.4 (5-7), 8.2 (7-10), and 14.9 (13-17) days, respectively, during the summer months. Young nymphs usually remain on or near the egg mass for the duration of the first instar. The first instar measures 1.1-1.5 mm long. Its color is predominantly black, though a protruding area at the lateral margins of the thorax and abdomen bears some yellow pigment, and there are yellow-white spots on the abdomen. During the second instar, nymphs wander away from the egg mass to feed, but generally they remain fairly aggregated. The second instar measures 2.2-2.5 mm long and is colored like the first instar, except for also bearing yellow-white spots on the thorax. The later instars are solitary and move freely about the plant to feed. The nymphs feed during the morning and late afternoon, seeking shelter during the heat of the day and cool of the night. They also seek shelter during periods of high wind and rainfall. The third instar measures 3.1-3.2 mm long. The anterior region of the bug is black, but fading to dark-green toward the posterior. The lateral margins turn from white to orange during this instar, and some yellow spots remain on the abdomen. The fourth and fifth instars measure 5.2-6.6, and 8.910.6 mm, respectively. They are pale green, with the lateral margins white with an orange edge, and some yellow spots on the abdomen. The wing pads become evident during the final two instars, especially the latter.
Stink Bug Nymphs
Say stink bug nymph.

Adult. The adults of Say stink bug are about 1216 mm long. Their color is green, but the shade varies considerably. The lateral borders of the pronotum, three spots on the anterior border of the scutellum, and the apex of the scutellum are yellow, orange, or red. The apical portion of the front wings are marked with small purple flecks along the veins. The adult of Uhler stink bug greatly resembles Say stink bug, though it lacks purple flecks on the membraneous portion of the front wings and usually lacks the orange color common at the tip of the scutellum in Say stink bug. Newly emerged adults are unable to oviposit immediately. A period of 20-30 days normally is required before adults mate and begin to deposit eggs. Females deposit eggs over a period of about one month. Total fecundity is estimated to average 54 per female, with a maximum of 107 eggs. This seems to be a fairly small number of eggs, however, and may represent the adverse consequences of caging. Overwintering adults and first generation nymphs feed principally on early-developing native plants. The second generation adults feed extensively on grain, and cause considerable damage. Later generations also feed on native plants because grains have matured and have been harvested. Unlike the nymphs, which seek shelter during the heat of the day, adults are active throughout the daylight hours. The adults are long-lived, reportedly persisting for 3-4 months in the summer. During the winter, of course, adults must survive for several months. Adults are often found overwintering under plant debris, bales of hay, and dried livestock droppings. A key to distinguish stink bugs commonly affecting vegetables is found in Appendix A. (See color figure 146.)

The most complete research of Say stink bug biology, conducted in New Mexico, was published by Caf-frey and Barber (1919). Patton and Mail (1935) contributed some observations from Montana. Buxton et al. (1983) described both species, and provided a key to close relatives.

Stem Plant With Seed Heads Alabama
Adult Say stink bug.

Damage

Nymphs and adults prefer to suck liquids from seeds and fruits, but if these are not available they feed readily on young leaf and stem tissue. Once seeds, including grain, begins to harden, the bugs no longer are able to feed. Thus, rapidly growing seeds are preferred. Seed heads of grains that have been attacked acquire a dull yellowish-white color, in contrast to the green appearance of undamaged heads. Such seeds are hollow, or nearly so. When fruit is attacked, the tissue adjacent to the feeding puncture does not develop as the fruit grows, leaving a blemish in the form of a depression. Foliar tissue that has been fed upon becomes wilted or discolored, and often dies.

Management

These stink bugs are dependent upon weeds for development of the first generations of the season. Thus, suppression of weeds is a recommended management practice to suppress stink bugs. However, with the immense amount of rangeland supporting suitable food plants in the western states, it is improbable that weed management would be effective in many areas. Many growers, therefore, depend solely on application of foliar insecticides for stink bug control. It is useful, however, to monitor weedy areas and field margins for stink bugs, because they are infrequently abundant enough to damage vegetable crops.

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