Distribution. This native species is found widely in the midwestern states and Great Plains region of the
United States from Kentucky west to Colorado and New Mexico.
Host Plants. Immaculate blister beetle has a fairly broad host range, and though it is especially often recorded as a pest of potatoes, it also attacks such vegetables as bean, beet, cabbage, onion, pea, pumpkin, radish, squash, and tomato. Post-bloom lima bean also is suitable, though pre-bloom plants are reportedly toxic. Other crops and flowers including alfalfa, sweet clover, hollyhock, gaillardia, and marigold can serve as hosts. Weeds including sunflower, Helianthus spp.; cactus blossoms, Opuntia sp.; wild lettuce, Lactuca sp.; Russian thistle, Salsola kali; and mullein, Verbascum sp.; also are consumed.
Natural Enemies. The natural enemies of immaculate blister beetle are not precisely defined, but undoubtedly are the same or similar to those affecting black blister beetle, Epicauta pensylvanica De Geer, and striped blister beetle, Epicauta vittata (Fabricius).
Life Cycle and Description. There is a single generation annually. In South Dakota, adults are present from June to August, but are most abundant in July. Eggs are present in July and August, and early instars through November. Overwintering occurs in instar six, with the final instar and pupation in May.
Immaculate blister beetle and its biology were described by Milliken (1921) and Gilbertson and Horsfall (1940). Werner (1945) and Pinto (1991) included this species in keys to North American Epicauta. Horsfall (1943) described a method of rearing blister beetles. Downie and Arnett (1996) provided keys to the eastern species of blister beetles, though it was derived from Werner's key.
Immaculate blister beetles are large and can cause extensive defoliation. Also, adults are quite gregarious and sometimes assemble in very large numbers.
Adult immaculate blister beetle.
Such aggregations can cause severe localized injury, though many nearby areas may escape with no visible damage. In most respects, the injury caused by immaculate blister beetle is equivalent to damage by other meloids. (See the discussion of damage in the section on black blister beetle for additional information.)
Blister beetles infrequently are vegetable crop pests, though they may become quite abundant during and following long-term grasshopper population increases, particularly populations of differential grasshopper, Melanoplus differentialis Thomas, and twostriped grasshopper, Melanoplus bivittatus (Say). As immaculate blister beetle is a large species and requires considerable food, the larvae develop successfully only in the presence of grasshoppers which produce large egg pods, such as differential grasshopper and twostriped grasshopper. Suppression of grasshoppers indirectly suppresses blister beetles by eliminating the food supply of the blister beetle larvae. Direct suppression of blister beetles usually does not occur in conjunction with chemical treatment of grasshopper populations because the grasshoppers occur earlier in the season, when blister beetles are still in the soil. Blister beetles are easily controlled by application of common insecticides to crop foliage, and small plantings can be protected with row covers or screening.
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