Acrosternum hilare Say Hemiptera Pentatomidae

Natural History

Distribution. This species, which is native to North America, occurs throughout the United States and southern Canada. It is less damaging, and therefore less well-known than southern green stink bug, Nezara viridula (Linnaeus). Although green stink bug is readily confused with southern green stink bug, the distribution of this latter species is limited principally to the southeastern states.

Host Plants. Green stink bug has a wide host range, though it is known principally as a pest of soybean and tree fruit. Among vegetables it has been observed to feed upon are asparagus, cabbage, corn, cowpea, cucumber, eggplant, lima bean, okra, mustard, pea, pepper, squash, snap bean, tomato, and turnip. Beans, particularly lima bean, are often damaged. Other common hosts are fruit such as apple, apricot, blackberry, cherry, elderberry, grape, mulberry, orange, pear, and strawberry; trees such as ash, basswood, black cherry, black locust, dogwood, hackberry, honey locust, holly, maple, and redbud; and field crops such as alfalfa, cotton, and soybean. Green stink bug may also be found on such weeds as common elder, Sambucus canadensis; goldenrod, Soli-dago spp.; jimsonweed, Datura stramonium; mallow, Malva spp.; mullein, Verbascum thapsus; and rattlebox, Crotalaria sp. Schoene and Underhill (1933) suggested that suitability of host plants changed through the season, and that stink bugs relocated as necessary. Availability of appropriate wild hosts early in the season is a prerequisite for high densities of green stink bugs in crops. McPherson (1982) provided a comprehensive list of hosts. Schoene and Underhill (1933) and Jones and Sullivan (1982) provided less complete lists but they indicated relative preference in Virginia and South Carolina, respectively.

Natural Enemies. Green stink bug is subject to attack by several natural enemies; McPherson (1982) and Jones et al., (1996) provided lists of the insect enemies. Eggs are parasitized by several wasps, but the most important seem to be Telenomus podisi Ash-mead, Trissolcus euschitis (Ashmead), and T. edessae (Fouts) (all Hymenoptera: Scelionidae), and Anastatus reduvii (Ashmead) (Hymenoptera: Eupelmidae). The late instar and adult bugs are attacked by Trichopoda pennipes (Fabricius) (Diptera: Tachinidae), a common parasitoid of hemipterans. Predators known to affect green stink bugs include predatory stink bugs (Hemi-ptera: Pentatomidae), green lacewings (Neuroptera: Chrysopidae) and various birds, particularly quail, Colinus virginianus. Yeargan (1979) studied the fate of stink bug eggs in two cropping systems and noted that green stink bug suffered less natural mortality than some other species of stink bugs. Also, mortality from unspecified chewing predators was more common than from parasitism, and mortality due to sucking predators was negligible.

Life Cycle and Description. The number of generations appears to vary. In Virginia (Underhill, 1934) and Ontario and Quebec (Javahery, 1990) it is reported to be one, but in Arkansas (Miner, 1966) and Kansas (Wilde, 1969) apparently there are two generations annually. In Arkansas, the first generation often occurs on dogwood, with the second generation attacking principally soybean. It would be easy to overlook the first generation, which may explain some of the disagreement about generation number. Development time is long, especially the adult pre-oviposi-tion period, so generation number is likely limited to one in the north, but the climate of southern states should allow a second generation. Photoperiod, rather than temperature, may determine generation number. Wilde (1969) reported that increasing day length stimulated egg production, whereas decreasing day length inhibited egg production. The life cycle requires about 100 days when stink bugs are cultured at 22°C. The adult is the overwintering stage. Adults become active in the spring when temperatures exceed about 21°C, and feed on young leaves and stems of trees.

  1. Oviposition in both Virginia and southern Canada does not occur until about mid-June, though in the midwestern states oviposition in early June has been observed. Eggs are normally deposited in clusters of about 30 eggs, though clusters of up to 69 eggs have been observed. The first egg cluster produced by a female is the largest, with subsequent clusters diminishing in size. The female is not very selective in her choice of oviposition site, with eggs deposited on both foliage and fruit. Mean egg production per female was estimated by Miner (1966) to average 60, but egg production of up to 170 per female was observed. The rearing conditions of Miner's study were suboptimal, and egg production likely suppressed. Javahery (1990) obtained oviposition of 130150 eggs per overwintered female, and this is probably a better estimate of fecundity. The mean incubation period at 22°C is 12.7 days (range 9-19 days). Incubation length decreases as temperature increases, with eggs hatching in only six days at 30-33°C. The eggs are deposited on end and in fairly definite rows, but the rows are not as tightly interlocked as in most stinkbug species. They are light green when first produced, but turn yellow and then pink as they mature. The cap of the egg becomes red immediately preceding hatch. The eggs measure 1.3-1.5 mm long, and 1.1-1.3 mm in diameter. The egg is somewhat cup-shaped, the top being slightly broader than the base. The top is ringed with a row of 45-65 small flattened processes (Essel-baugh, 1946).
  2. The eggs from the overwintering adults begin to hatch in July, though overwintered females continue to produce eggs throughout the summer. Nymphs tend to remain aggregated during the first instar, but disperse thereafter. Mean duration (range) of the five instars is 7.0 (5-10), 8.9 (6-14), 7.9 (6-11), 8.9 (6-11), and 12.8 (8-20) days, respectively, when reared at 22°C on soybean (Miner, 1966). Development times are shorter when reared on apple, pear, and snap bean at 23°C, averaging 6, 6-7, 6-8, and 8-9 days, respectively, for instars 1-5 (Javahery, 1990). Simmons and Yeargan (1988a) studied development over a range of temperatures and observed fastest development at 27°C, with the egg to adult stage completed in about 40 days, whereas nearly 50 days were required at 24° and 30°C, and 70 days at 21 °C. The nymphs measure about 1.6-2.0, 2.3-3.2, 4.0-5.2, 6.8-8.2, and 10.012.7 mm long for instars 1-5, respectively. In color, the dorsal surface of instars 1-4 tends to be brownish-black on the head and thorax, with a yellow spot centrally and yellow at the lateral margins of the thorax. The abdomen is marked with transverse black and light-blue stripes, and large black spots centrally. The lateral margins of the abdomen bear a row of semi-elliptical spots, blackish-bronze in color. The fifth instar differs from the earlier instars, as the abdomen lacks stripes, and is rather uniform yellow-green in color.
  3. Nymphs from the first generation begin to attain the adult stage in August. Adults begin feeding within a few hours of attaining the adult stage, but mean days to copulation by adults is 22.3 (range 1130 days). Mating requires only a few minutes, but sometimes persists for several hours. Females usually mate after each egg cluster is deposited. Another 21.7 (19-33) days are required, following copulation, until egg production commences. Duration of the adult stage is about two months during the summer, but
Hemiptera Nymph
Nymph of green stink bug, dark form.

several months during the winter. With the onset of cold weather, adults disperse to wooded areas. Overwintering occurs in leaf litter, and under bark of trees, in wooded areas. The adult bugs measure 13-19 mm long. They are largely uniform green in color, though the dorsal surface is darker than the ventral, and the edges of the head, pronotum, and abdomen are marked with yellow. The three distal segments of the antennae are marked with brownish-black.

Southern green stink bug, N. viridula (Linnaeus), is easily confused with green stink bug, A. hilare. However, the two species differ ecologically and morphologically. Acrosternum hilare is usually associated with trees and shrubs, rather than the herbaceous vegetation fed upon by N. viridula. Also, A. hilare is found widely in North America, though it is most abundant in the north. The two species can be differentiated by the shape of the abdominal spine. When viewed from below, A. hilare has a pointed spine protruding forward between the base of the hind legs whereas in N. viridula, the spine is rounded.

Male green stink bugs produce an aggregation pheromone that attracts both males and females, other stink bug species, and the tachinid parasitoid Tricho-poda pennipes (Aldrich et al., 1989). The pheromone consists of the same chemicals found in the phero-mone of southern green stink bug, but the ratios are different.

The biology of green stink bug was given by Whit-marsh (1917), Underhill (1934), Miner (1966), and Javahery (1990). Developmental biology was described by Simmons and Yeargan (1988a). Nymphs were described by Whitmarsh (1917) and Decoursey and Esselbaugh (1962). Culture on plant tissue was provided by many authors, such as Wilde (1968); culture on artificial diet was presented by Brewer and Jones (1985). A key to the common stink bugs found in vegetables is included in Appendix A.

Trissolcus Near
Adult green stink bug.

Damage

The green stink bug inserts its beak into fruit or foliar tissue and removes liquids. During feeding, the bug injects enzymes that liquefy plant tissue and cause the tissue at the feeding site to collapse. Subsequently, tissue adjacent to the feeding site continues to grow, but the tissues at the feeding site fail to grow, leading to dimples or similar deformities. Feeding sites also may become discolored, usually turning black and hardened, but sometimes white and spongy. Adults and nymphs inflict the same type of injury.

Damage potential varies considerably among insect stages. The first instar does not feed. Feeding frequency increases as the nymph matures, with the fifth instar feeding most frequently, an average of 3.4 times per day. Duration of each feeding session does not vary with bug age, however, averaging 1.5 h per session. The adults and fifth instars, and both sexes, displayed similar feeding behaviors (Simmons and Yeargan, 1988b). Plant responses to green stink bug feeding have not been well studied, but some states recommend treatment of beans if stink bug abundance attains 1 bug per 5 m of row.

Green stink bug harbors Nematospora coryli, a fungus that causes yeast-spot disease in beans and soybeans. Both adults and nymphs acquire the pathogen by feeding, retain it in their bodies, and excrete it in their saliva and feces (Foster and Daugherty, 1969; Clarke and Wilde, 1970). The pathogen greatly exacerbates the damage caused by green stink bug. Underhill (1934) reported the loss of entire lima bean crops due to this disease and its insect vector. Other fungi and bacteria can be transmitted by stink bugs (Russin et al., 1988), so the vector potential of green stink bug may not be limited to transmission of N. corylii.

Management

  1. Stink bug populations tend to be highest at field margins, probably reflecting the tendency of adults to overwinter in wooded areas surrounding fields, and the early season feeding preference for trees. Sampling in soybean is usually accomplished by shaking the plant over soil or a drop cloth, and counting the insects dislodged, but visual examination may be appropriate for crops with less vegetation. In all crops, sampling for eggs is done by visual examination.
  2. Stink bugs often are difficult to kill, but proper selection and timing of foliar insecticides can protect crops from injury. Residual materials are usually desirable because the stink bugs often develop outside the crop and enter at various times. It is most important to protect the crop during the blossom and early fruiting stage. Because bugs are entering from the crop margins, border treatments may be adequate.

Cultural Practices. Stink bug populations increase during the season, with maximum densities and damage occurring late in the growing season. Stink bugs commonly enter crop fields from adjacent vegetation, either woodlands or weedy areas. Thus, a common recommendation is to plant as early as possible to avoid peak insect abundance. However, in studies conducted with soybean, early plantings (early June) were as damaged as late (early July) (McPherson et al., 1988). Jones and Sullivan (1982) suggested that destruction of black cherry and elderberry would greatly reduce abundance of green stink bug. Trap crops also are sometimes recomended for stink bugs. For information on this subject, see the discussion on trap crops in the section on southern green stink bug. Pole beans are considered more susceptible than bush varieties (Underhill, 1934).

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