Blissus leucopterus Say Hemiptera Lygaeidae

Natural History

Distribution. The chinch bug, Blissus leucopterus, is found through much of the eastern United States and southern Canada, west to about the Rocky Mountains. However, it is absent from the Gulf Coast region, where it is replaced by a closely related species, the southern chinch bug, Blissus insularis Barber. The two species have overlapping ranges in portions of the southern states from North and South Carolina through central Georgia and west to Texas. Southern chinch bug feeds only on lawn and forage grasses, particularly St Augustine grass, and is not a food-crop pest. Other species of Blissus occur in both eastern and western states but they are of little consequence. The Blissus spp. may have dispersed northwards from South America, but if it is so they apparently dispersed in pre-colonial times, as there is no record of their introduction.

The range of B. leucopterus can be subdivided because two discrete subspecies exist; B. leucopterus hirtus Montandon in the northeast, and B. leucopterus leucopterus (Say) in the central region of the eastern states. In eastern Canada, the New England states, and south to about northern Virginia and eastern Ohio, the northeastern form, B. leucopterus hirtus, is a pest of lawn grasses, but not of food crops. This subspecies is also called "hairy chinch bug" to distinguish it from the food crop-attacking subspecies, B. leucop-terus leucopterus, which is known simply as "chinch bug." Chinch bug occurs from Virginia to Georgia in the east, extending to South Dakota and Texas in the west. Chinch bug generally is not damaging throughout its entire range, and is considered to be a pest mostly in the midwestern and southwestern states from Ohio in the east to South Dakota and Texas in the west.

Host Plants. Hosts of chinch bug consist solely of plants in the family Gramineae, but include both wild and cultivated grasses. It is known principally as a pest of such grain crops as barley, corn, millet, oat, rye, sorghum, and wheat, but oat is only marginally suitable. Among vegetables, only corn is damaged. However, it also damages forage grasses including sudangrass and timothy, and feeds on wild grasses such as foxtail, Setaria spp.; crabgrass, Digitaria spp.; and goosegrass, Elusine indica (Ahmad et al., 1984).

Females select sorghum for oviposition over wheat and corn; barley is intermediate in preference. Crop suitability, as measured by development time, is similar to oviposition preference (M.T. Smith et al., 1981).

Natural Enemies. Numerous natural enemies have been observed. Among avian predators feeding on chinch bugs are common birds as barn swallow, Hirundo erythrogastra Boddaert; horned lark, Otocoris alpestris (Linnaeus); meadowlark, Sturnella magna (Linnaeus); redwinged blackbird, Agelaius phoeniceus (Linnaeus); and kingbird, Tyrannus tyrannus (Linnaeus).

Insect predators of special importance are insidious flower bug, Orius insidious (Say) (Hemiptera: Antho-coridae), an assassin bug, Pselliopus cinctus (Fabricius) (Hemiptera:Reuviidae), and various ants (Formici-dae). Lady beetles (Coleoptera: Coccinellidae) and lacewings (Neuroptera: Chrysopidae) frequently have been observed on plants infested with chinch bugs, but their effects are uncertain.

Parasitoids are sometimes found in these small insects, but rarely are they considered to be significant mortality factors. An egg parasite, Eumicrosoma benefica Gahan (Hymenoptera: Scelionidae), the nymphal or adult parasite Phorocera occidentalis (Walker) (Diptera: Tachinidae), and an unspecified, naturally occurring nematode have been reported. The egg parasitoid, which is found throughout most of the range of the chinch bug and is active during much of the season when chinch bug occurs, was reported to parasitize up to 46% of the eggs in Nebraska, so it may be of considerable value in biological control (Wright and Danielson, 1992). Also, chinch bugs are susceptible to infection by the entomopathogenic nematodes Steiner-nema spp. (Nematoda: Steinernematidae), but the dry environment inhabited by chinch bug is not very suitable for movement and infection by nematodes.

The most important natural mortality factor is fungal disease, particularly Beauveria bassiana. Interestingly, this fungus was intensively redistributed, particularly in Kansas, during the late 1880s in an effort to increase suppression. However, it eventually became apparent that the disease spread naturally, and that the effectiveness of the fungus was related more to weather than to the efforts of agriculturalists and entomologists to foster epizootics. The fungus is invasive and pathogenic at relative humidities of 30-100%, but fungal replication and conidia production require humidities of at least 75% (Ramoska, 1984). Clumps of such bunch grasses as little bluestem, Andropogon sco-parius, serve to harbor not only overwintering bugs, but Beauveria as well (Krueger et al., 1992), and may be important in initiating fungal epizootics. The food plant of the chinch bug affects susceptibility to B. bassi-ana, with a diet of corn and sorghum suppressing fungus development and bug mortality (Ramoska and Todd, 1985).

Weather. Weather has significant impact on chinch bugs. The overwintering period is moderately critical. The adults seek shelter in stubble and debris, but one of the most favorable locations is among the stems of bunch grasses. Bunch grasses provide food in the autumn before the onset of winter temperatures, and again in the spring before it is consistently warm and the bugs disperse. Bunch grasses also serve to break the wind by reducing desiccation and the sever ity of the wind, and by keeping excessive rainfall from the insects. Thus, in the absence of bunch grasses or similar shelter, survival can be poor. Heavy snow cover is favorable, keeping the bugs warmer and sheltered from the drying wind.

Summer weather is perhaps even more critical. Chinch bugs thrive in warm, dry conditions, at least in the midwestern states. Heavy rainfall can kill many bugs, and wet, humid weather fosters epizootics of fungal disease. In the southwest the situation is different because dry weather is usually assured, but the absence of summer rain causes premature senescence of plants, depriving bugs of green food late in the summer.

Life Cycle and Description. There are at least two generations per year throughout the range of B. leucop-terus leucopterus. The first generation commences in the spring, with oviposition by overwintering adults, usually in April or May. The second generation begins in June-August. Second generation adults overwinter, often in the shelter of clump-forming wild grasses, dispersing in the spring to early-season crops, and then in early summer to later-developing crops where the second generation develops. Generations overlap considerably due to prolonged oviposition, and in the southwestern states there is some evidence of a third generation. A complete life cycle can occur in about 30-60 days.

  1. The elongate-oval eggs are rounded at one end, truncate at the other, and measure about 0.85 mm long and 0.31 mm wide. The truncate end bears 3-5 minute tubercles, 0.1 mm long. The eggs are whitish initially, turning yellowish-brown after a few days and reddish before hatching. The eggs are deposited in short rows at the base of the plant on roots, on the lower leaf sheaths and stems, and on the soil near the plant. Females deposit eggs at a rate of 15-20 per day over a two- to three-week period, producing up to 500 eggs. Duration of the egg stage is about 16 days at 27°C and eight days at 31°C.
  2. There are five instars. Duration of the instars is about 5, 6, 5, 4, and 6 days for instars 1-5, respectively, when reared at 29°C. Under field conditions the development time may be extended, with a period of about 30-40 days considered normal, and 60 days not unusual. During the early instars the head and thorax are brown, and the legs are pale. These structures become darker as the nymphs mature, so the mature nymph is blackish. The first two segments of the abdomen are yellowish or whitish, the remainder is red except for the tip of the abdomen, which is black. The reddish abdomen becomes progressively

Chinch bug nymph.

darker, however, appearing almost black at nymphal maturity. The wing pads become visible in the third instar, but are difficult to discern. In the fourth instar the wing pads extend about half the width of the first abdominal segment, whereas in the fifth instar they extend to the third abdominal segment. The nymphal body lengths are about 0.9,1.3,1.6, 2.1, and 2.9 mm for instars 1-5, respectively. Nymphs prefer to feed in sheltered locations such as curled leaves and on roots, but are often found aggregated on the stem near the base of the plants. When not feeding they may hide under clods of soil and rubbish, or in loose soil. (See color figure 142.)

Adult. The body and legs of the adult are blackish. The wings of B. leucopterus leucopterus nearly attain the tip of the abdomen, and are white in color with a pronounced blackish spot found near the center and outer margin of the forewings. The adult measures 3.54.5 mm long. The black-spotted white wings serve to distinguish the chinch bug from similar crop-damaging species such as false chinch bug, Nysius spp. In the related form of hairy chinch bug, the wings generally are abbreviated, usually not extending beyond the middle of the abdomen.

There are numerous publications on chinch bugs, though many of the early works treated B. leucopterus leucopterus, B. leucopterus hirtus, and B. insularis as synonymous. A bibliography was published by Spike et al. (1994). Perhaps the most useful publications on biology were Webster (1907) and Luginbill (1922b), though Swenk (1925) presented a very good synopsis. Leonard (1966, 1968) revised the eastern Blissus, and provided descriptions and keys. Culture techniques were described by Parker and Randolph (1972), and Ramoska and Todd (1985).

Damage

Chinch bug is a plant sap-feeding insect, causing a reddish discoloration at the site of feeding and death

Adult chinch bug.

of that portion of the plant. Plant growth can be stunted, or plants killed when fed upon by numerous bugs. Their destructiveness is attributable, in part, to their gregarious nature. Not only do many bugs aggregate on certain plants, but they also disperse in tremendous numbers from field to field. Bugs at densities of 10-20 per young plant reduce growth rate of corn (Negron and Riley, 1985). When plants are infested while young they suffer more damage than if infested later in growth (Negron and Riley, 1990). It rarely is reported as a sweet corn pest, however.

Management

Insecticides. Granular and liquid insecticides are used to protect plants, particularly fields that are invaded by nymphs or adults dispersing from senescent early-season crops. Systemic insecticides can be applied at planting time, and either contact or systemic materials are used after the crop has emerged from the soil (Peters, 1983; Wilde et al., 1986). Liquid insecticides should be directed to the base of the plants—a location favored by the insects.

Cultural Practices. Historically, most damage occurred when early-season small-grain crops were matured, and large numbers of first generation nymphs dispersed by walking to adjacent crops, usually corn. This was combated by erecting barriers, usually in the form of a ditch, between crops. Also, some destruction of overwintering bugs in wild grasses was accomplished by burning, though it was only 50% effective. These practices are largely obsolete, and insecticides are now used effectively. However, it is advisable to rotate among susceptible and nonsusceptible crops, and to grow susceptible crops in isolation from alternate hosts. Because the combination of small grains and corn leads to damage by chinch bugs, it may be desirable to eliminate one of these crops and thereby eliminate an important foods from the chinch bug life cycle. In southern states the crop sequence is different, with both wheat and corn invaded by overwintering bugs early in the season (Negron and Riley, 1991).

Cultural practices that promote dense growth and shade will increase humidity and decrease chinch bug numbers. Thus, fertilization and irrigation can be detrimental to chinch bug survival.

Host-Plant Resistance. There is considerable difference among crops in susceptibility to injury, and within crops the level of resistance also is variable. For example, Stuart et al. (1985) examined resistance among wheat cultivars, though not because the bugs are a great problem in wheat but because they disperse from wheat to sorghum, where damage is more likely. They reported measurable levels of difference in longevity, development, and reproduction of bugs fed different varieties, but concluded that there was not a practical level of resistance. In contrast, Wilde and Morgan (1978) identified a resistant variety of sorghum, and Flint et al. (1935) reported considerable resistance in grain corn.

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Responses

  • How to control chinch bugs organically?
    8 years ago
  • birgit
    Why has there been an increase in coridae insects lately?
    6 years ago

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