Diabrotica balteata LeConte Coleoptera Chrysomelidae

Natural History

Distribution. Banded cucumber beetle is a tropical insect. Before 1910, its distribution in the United States was limited to southern Arizona and Texas (Saba, 1970). Now it is distributed all over the southern United States from North Carolina to southern California, and south through Mexico and Central America (Krysan, 1986). Although, it has spread rapidly in the United States, its intolerance to freezing temperatures probably limits its northward distribution to its current status. Saba (1970) observed poor survival of all stages at 0°C, and no survival below 0°C.

Host Plants. Adults feed on a wide range of plants, but seem to prefer plants from the family Cucurbitaceae, Rosaceae, Leguminoseae, and Cruci-fereae (Saba, 1970). Vegetable crops damaged include cucumber, squash, beet, bean, pea, sweet potato, okra, corn, lettuce, onion, and various cabbages (Chitten-den, 1912a; Saba, 1970). Despite the common name, bean and soybean are especially favored and in tropical countries this insect is commonly viewed as a bean pest (Cardona et al., 1982).

Natural Enemies. Except for nematodes, the natural enemies of banded cucumber beetle are poorly known. The mermithid nematode, Filipjevimermis leip-sandra (Poinar and Welch), affects this species, as well as spotted cucumber beetle and several flea beetle species (Creighton and Fassuliotis, 1980). In banded cucumber beetle, natural infection levels in South Carolina peaked in late summer, but levels in the range of 20-40% were common from May through October. F. leipsandra reproduces parthenogenetically and has a life cycle duration of 65-70 days under favorable conditions (Cuthbert, 1968). The heterorhabditid nematode Heterorhabditis heliothidis (Khan, Brooks, and Hirschman), has also been isolated from field populations of banded cucumber beetle (Creighton and Fassuliotis, 1985), but it is uncertain whether this nematode is an important natural mortality factor. Ants have been shown as important egg predators in the tropics (Risch, 1981) and likely are important elsewhere.

Life Cycle and Description. Banded cucumber beetle does not enter diapause (Saba, 1970). It remains active as long as the weather remains favorable, with up to 6-7 generations per year reported in Louisiana (Pitre and Kantack, 1962) and Texas (Krysan and Branson, 1983). Under optimal conditions, a life cycle can be completed in 45 days.

  1. The eggs are yellow, oval in form, and measure about 0.6 mm long and 0.35 mm wide. They are deposited in cracks in the soil, and 5-9 days normally are required before hatching (Marsh, 1912a).
  2. The three instars have mean head capsule widths measuring about 0.24, 0.35, and 0.51 mm, respectively. The body length during these instars is reported to be about 2.3, 4.5, and 8.9 mm. Larval color is somewhat variable; initially it is white, but may also take on a pale-yellow color, depending on the food source. Development time is temperature dependent, but the range is about 4-8, 3-11, and 4-15 days for instars 1-3, respectively. Total larval development time is usually 11-17 days.
  3. Pupation occurs in the soil, with a duration of 4-6 days.
  4. The adults are 5-6 mm long, greenish yellow, with a red head and black thorax. Usually there are three transverse bands across the elytra, green in color but sometimes with a bluish tint, and a thin green band running down the center of the insect's back. The banding pattern is variable, and sometimes almost absent (Chittenden, 1912a). Copulation occurs about six days after adult emergence, whereas egg deposition begins about 16 days later. Oviposition takes place at 2-3-day intervals for 2-8 weeks. Females normally deposit 2-15 egg clusters up to 100 eggs each. A total of 850 eggs may be produced by a female. Adult longevity is 17-44 days, but averages 26 days. (See color figure 112.)

Detailed information on banded cucumber beetle biology was provided by Pitre and Kantack (1992), and Saba (1970). Rearing techniques were provided

Diabrotica Balteata Cerotoma
Adult banded cucumber beetle.

by Schalk (1986). Biosystematics of Diabrotica spp. was presented by Krysan and Branson (1983).

Damage

Banded cucumber beetle is nearly omnivorous, and in addition to numerous plants being attacked, all parts of the plant are injured. Marsh (1912a), for example, noted damage to foliage, blossoms, silk, kernels, the plant crown, and roots. Larvae feed only on the roots. The most frequent forms of serious injury are defoliation by adults and root feeding on plant seedlings by larvae. Some of the most serious injury results from larval feeding on sweet-potato roots. There are no reports of cucurbit wilt transmission by banded cucumber beetle, but this species is much less well studied than striped and spotted cucumber beetles. Banded cucumber beetle is known as a vector of virus diseases in beans (Cardona et al., 1982; Gergerich et al., 1986), and Latin and Reed (1985) suggested that larval feeding might increase the incidence and severity of Fusarium wilt.

Management

  1. A female-produced sex pheromone has been identified (Chuman et al., 1987).
  2. Insecticides are sometimes used to prevent damage to roots by larvae. Most often, granular insecticides are applied in a band over the row, either at time of planting or soon thereafter. Foliar insecticides are sometimes needed to prevent excessive damage to seedlings, but adults are rarely abundant enough to warrant control on large plants.

Biological Control. Two nematodes have been well studied for suppression of banded cucumber beetle: the mermithid, F. leipsandra and the heterorhabdi-tid, H. heliothidis. Creighton and Fassuliotis (1983) induced high levels of parasitism in banded cucumber beetle larvae by F. leipsandra with application of nema-

tode eggs to field microplots. This nematode also infects several other chrysomelids. Some progress toward mass production of the nematode also has been reported (Creighton and Fassuliotis, 1982), but the nematode is not available commercially. Hetero-rhabditis heliothidis was found naturally parasitizing banded cucumber beetle (Creighton and Fassuliotis, 1985), and effectively reduced beetle larval numbers in trials with potted plants. Although H. heliothidis is not available commercially, the related Steinernema nematodes are effective under experimental conditions (Poinar, 1979) and are readily available.

Fungi have been evaluated experimentally for banded cucumber beetle control (Bell et al., 1972). Beauveria bassiana and Metarhizium anisopliae infected both larvae and pupae, but Spicaria rileyi was relatively ineffective.

Cultural Practices. The wide host range of this insect, which includes many weed species (Saba, 1970) suggests that clean cultivation or some other form of weed control would be valuable in reducing damage to seedlings. Adults can be kept from attacking seedlings through use of screening or row covers.

Host-Plant Resistance. Cultivars of sweet potato partially resistant to cucumber beetle injury are known (Schalk and Creighton, 1989), but this information seems lacking for other plants.

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