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.
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.
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.
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.
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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