Epicauta vittata Fabricius Coleoptera Meloidae

Natural History

Distribution. The striped blister beetle, Epicauta vittata (Fabricius), is a native species and eastern in distribution. It has been collected from all eastern states west to, and including, South Dakota, Nebraska, Kansas, and Oklahoma. In Canada, it is known from Quebec and Ontario. Populations from the southeastern coastal plain including Florida, southern Georgia, and eastern South Carolina differ in appearance from beetles found elsewhere and are called the "lemniscate race," but interbreed successfully with normal beetles. Also see the discussion of blister beetles in the section on black blister beetle, Epicauta pensylvanica (De Geer).

Host Plants. Vegetable crops such as bean, beet, carrot, cabbage, Chinese cabbage, corn, eggplant, melon, mustard, pea, pepper, potato, radish, spinach, squash, sweet potato, tomato, and turnip are sometimes injured. Clover and soybean can also be attacked. Pigweed, Amaranthus spp., is highly preferred by adults.

Natural Enemies. Little is known concerning the natural enemies of striped blister beetle, though Ingram and Douglas (1932) reported consumption by robber flies (Diptera: Asilidae) and avian predators, including meadowlark, Sturnella neglecta Audubon; bluebird, Sialia sialis (Linnaeus); and scissor-tailed flycatcher, Muscivora forficata (Gmelin). Selander (1981, 1982) reported predation of striped blister beetle eggs by the predatory blister beetle, Epicauta atrata (Fabricius). See the section on black blister beetle for further discussion on natural enemies.

Life Cycle and Description. There are 1-2 generations per year. In Arkansas, the May-June or early-emerging adults go on to produce another generation in which adults emerge in September. Maximum emergence of adults occurs in July, however, and few of the later-emerging adults contribute to the second generation. The generations overlap, resulting in adults present in the field from late-May to late-October. Overwintering occurs as instars five and six. In Florida, the season is considerably advanced, with most adults found during April-June.

  1. The eggs of striped blister beetle are whitish and average about 1.8mm long and 0.7mm wide, though they vary greatly in size, with the length ranging from 1.4-2.1 mm. In shape, they are elongate oval, with rounded ends. The eggs are deposited in the soil within a tubular chamber 3-4 cm deep, normally in clusters of 100-200 eggs. The female covers the eggs after oviposition, and hatching occurs in 10-16 days. Eggs can be found from June-September in Arkansas. Females are reported to produce several hundred eggs in captivity, though this estimate may be low, because many closely related species produce 2000-3000 eggs during the life span of 20-50 days (Adams and Selan-der, 1979).
  2. As is typical with blister beetles, the larval form initially has long legs and is quite mobile. The legs become reduced in size, however, as the larva develops, and instars 6-7 (if present) have small head capsules and do not feed. Newly hatched larvae are whitish but soon turn reddish brown with dark brown bands on the thorax and abdomen. The first instar must disperse from the egg mass and can locate grasshopper eggs on which to feed. Once locating a grasshopper egg pod, the larva feeds and molts at short intervals. The mean duration of the first five instars, all of which feed on grasshopper eggs, is 3.4,1.2, 1.1, 1.6, and 11.3 days, respectively, at warm temperature. Overwintering also may occur in the fifth instar, followed by pupation in the spring. Alternatively, larvae may display a sixth and seventh instar before pupation, with the sixth instar persisting for about 230 days and the seventh for 6-14 days. Seventh instars are found in April-July at about the same time other individuals are pupating or emerging as adults. Mean larval head capsule widths (range) are 0.63 (0.53-0.82), 0.83 (0.75-0.91), 1.10 (0.93-1.20), 1.64 (1.37-1.75), 2.28 (2.18-2.37), 1.73 (1.37-2.18), and 2.42 (1.75-2.68) mm for instars 1-7, respectively.
  3. The pupal stage is found in the soil. The pupa greatly resembles the adult, though the wings and legs are tightly drawn to the ventral surface. Initially the pupa is whitish, but becomes darker with maturity. Duration of the pupal stage is 9-13 days. Pupae are found in May-August.
  4. The adults measure 9-17 mm long and are black and yellow. The color pattern varies geographically, but normally two black spots occur dorsally on the head and on the thorax, and the elytra each bear two or three black stripes. Northern populations often bear only two black stripes on the elytra, whereas southern populations usually bear three black stripes. The southern Coastal Plain race, which has three stripes on each elytron, is termed the lemniscate race. Like most other blister beetles, the adult is elongate and slender, the thorax is narrower than the head and abdomen, and the legs and antennae are moderately long. The body bears numerous small punctures, and is densely clothed with short hairs. The elytra are long, covering the abdomen but separated or divergent at the tips. The hind wings are transparent.

The adults are most active during the morning and late afternoon, seeking shelter from the sun at midday. In particularly hot and arid climates, they remain inactive during the day, confining activity to the evening hours. They are easily disturbed, dropping readily from the plant and hiding or scurrying away if disturbed. Pheromonal cues are likely involved in aggregation behavior, but this is poorly defined. The pre-ovipositional interval of striped blister beetle is about 20 days, with a 10 day interval between production of egg masses. (See color figure 100.)

The adults of striped blister beetle are very similar to Epicauta occidentalis Werner and E. temexa Selander and Adams, and these species frequently have been confused in the literature. Also, "Epicauta lemniscata" has been used for reference to these species, and to mixed populations of these species. Adams and Selan-der (1979) provided a detailed description of striped blister beetle, and keys to separate this species from close relatives. The biology of striped blister beetle is included in the publications of Gilbertson and Horsfall (1940) and Horsfall (1943). Werner (1945) and Pinto (1991) included this species in keys to North American Epicauta. Downie and Arnett (1996) provided keys to the eastern species of blister beetles, though these are derived from Werner's. Horsfall (1943) described a method of rearing blister beetles.

Damage

Striped blister beetle is one of the most damaging of the blister beetles to vegetable crops in areas where it occurs. This is owing to its feeding preferences, which include several common crops and greater preference for foliage than other species; its propensity to feed on fruits of solanaceous plants; its relatively large size and voracious appetite; its strong tendency to aggregate into large mating and feeding swarms; and its high degree of dispersiveness, which can result in

sudden appearance of large swarms of beetles. It also has been implicated in the transmission of bean pod mottle virus to soybean; this is not surprising because other beetles also are associated with spread of this disease (Patel and Pitre, 1971). In other respects, damage by striped blister beetle is nearly identical to black blister beetle, Epicauta pensylvanica De Geer. (See the section on black blister beetle for a thorough discussion of damage.)

Management

Insecticides. Blister beetle populations are easily controlled by foliar application of insecticides. The tendency of beetles to aggregate, however, may result in serious defoliation in small areas of a field, and little or no damage elsewhere. Thus, careful visual examination of plants is suggested, followed by spot treatment of infested areas.

Cultural Practices. Striped blister beetle is reportedly closely associated with grasshoppers that produce large egg pods, particularly twostriped grasshopper, Melanoplus bivittatus (Say) and differential grasshopper, M. differentialis Thomas. Thus, environments that favor these grasshoppers, such as an abundance of alfalfa, also favor occurrence of the blister beetles. However, young blister beetles may be present in the summer before these grasshoppers have produced egg pods, so Horsfall (1943) suggested that other, early maturing species of grasshoppers may be necessary to provide eggs to bridge the gap between the hatch of beetle larvae and the appearance of new M. bivitta-tus and M. differentialis eggs. This suggests that blister beetle abundance can be regulated not only by practices which affect grasshopper abundance, but that disruption of either the early season or late season species would be disruptive to striped blister beetle.

Striped blister beetle adult feeds readily on alfalfa, and can be abundant in this crop even in the absence of grasshoppers. The association of striped blister beetle with alfalfa implies that vegetable crops grown in proximity to alfalfa are at greater risk, and that the risk is elevated when alfalfa is harvested. Small crop plantings can be protected from blister beetles with row covers or screening.

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