Epicauta maculata Say Coleoptera Meloidae

Natural History

Distribution. This native species occurs primarily in the Great Plains region of North America. It is abundant from southern Manitoba and Saskatchewan south through the western plains to central Mexico and Guatemala. It is rare east of Iowa, and occurs west of the Rocky Mountains only in Arizona. There are other spotted blister beetles with which it can be confused, but there is little overlap in the geographic distribution. Also see the discussion of blister beetles in the section on black blister beetle, Epicauta pensylvanica (De Geer).

Host Plants. Spotted blister beetle is reported from such vegetable crops as bean, beet, cabbage, potato, and spinach. Other crops affected include alfalfa, soybean, and sweet clover. Weed hosts include silver-leaf nightshade, Solanum elaeagnifolium; and lambsquar-ters, Chenopodium album.

Natural Enemies. Natural enemies are poorly known. For discussion of natural enemies of blister beetle, see the sections on black blister beetle, Epicauta pensylvanica De Geer, and striped blister beetle, Epicauta vittata (Fabricius).

Life Cycle and Description. The life cycle of spotted blister beetle is not as clearly defined as some of the other blister beetles. In most cases, only a single generation per year occurs, but in some cases larvae do not diapause, so the possibility exists of a second generation. The adult of this species is one of the last blister beetles to emerge and, as with other Epicauta spp., late instars overwinter.

  1. The eggs are elongate oval, with rounded ends. Eggs measure about 1.2 mm long and 0.5 mm wide, and are whitish in color. The female deposits 50-100 eggs per egg mass within a cavity in the soil. The egg cavity is reported to be flared or bell-shaped, wider at the bottom than at the top, and to extend to a depth of about 2.5 cm. Duration of the egg stage is 10-21 days.
  2. This insect is not as well-studied as some other blister beetles, so knowledge of the developmental biology is incomplete. In most respects, morphology and development should be equivalent to that of black blister beetle, Epicauta pensylvanica, with five instars developing on grasshopper eggs followed by two non-feeding instars. Mean duration of the first five, or feeding, instars of spotted blister beetle is 4.1, 1.6,1.5, 2.0, and 13.6 days, respectively. The larvae are yellowish in color.
  3. The pupal stage resembles the adult, though the wings and legs are drawn under the body. It is yellowish white and measures about 10 mm long. Like the larval stage, it occurs in the soil.
  4. The adult is small, measuring 6-12 mm long, and moderately elongate and slender. It is black but densely clothed with short-gray or olive-gray hairs; this pubescence imparts a grayish color to the beetles. The pubescence is absent in small to moderately sized spots, particularly on the elytra, which produces the black-spot pattern that is the basis for the common name of this species. As is typical with this family, the thorax is narrower than the head and abdomen, and the legs and antennae are moderately long. The elytra are long, covering the abdomen but separated or divergent at the tips. The hind wings are transparent. (See color figure 102.)

Spotted blister beetle and its biology were described by Milliken (1921), Gilbertson and Horsfall (1940), and Pinto (1980). Werner (1945) and Pinto (1991) included this species in keys to North American Epicauta.

Epicauta Maculata
Adult spotted blister beetle.

Horsfall (1943) is a good source of information on all the common Epicauta spp. and he described a method of rearing blister beetles. Downie and Arnett (1996) provided keys to the eastern species of blister beetles, though their key was derived from Werner's 1945 key; Werner et al. (1966) provided keys to blister beetles in the southwest.

Damage

The adult blister beetles cause injury by defoliating plants, though they are relatively small beetles, and less damaging than those of the larger species because they eat less. Beetles tend to aggregate, apparently in mating swarms, so damage can be significant in relatively small areas of a crop and is absent or trivial elsewhere. Although adults of spotted blister beetle inflict damage to vegetable crops through consumption of foliage, in some instances they prefer blossoms, and larvae are beneficial due to their consumption of grasshopper eggs. For a more complete discussion of the damaging and beneficial aspects of blister beetles, see black blister beetle, Epicauta pensylvanica.

Management

Blister beetles are not often vegetable crop pests, though they may become quite abundant during and following long-term grasshopper population increases. Gilbertson and Horsfall (1940) reported that spotted blister beetle was generally associated with eggs of migratory grasshopper, Melanoplus sanguinipes (Fabricius) though certainly larger grasshopper species with larger egg pods would also be suitable hosts. Suppression of grasshoppers indirectly suppresses blister beetles by depriving the beetle larvae of grasshopper eggs. Blister beetles also are easily controlled with foliar applications of common insecticides, and small crop plantings can be protected with row covers or screening.

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