Systena elongata Fabricius Coleoptera Chrysomelidae

Natural history

Distribution. Palestriped flea beetle is widely distributed in the United States. It is found from New York to Florida on the east coast and west to California. This native pest is rare or absent in the northern states from New England to Washington. Its pest status seems to be limited to the central United States from Virginia to Colorado. In Canada, this flea beetle is known from Alberta and Ontario, but is so infrequent as not to be considered a pest.

A closely related species, elongate flea beetle, is found over the same geographic area. However, it is most abundant in the southeastern United States. In Canada, it is known only from Manitoba. Rarely it has been known to reach damaging levels of abundance.

Host Plants. A very broad range of plants is eaten by the adults of S. blanda. Elongate flea beetle, although less well-known, seems to have a very similar host range. Vegetable crops reported to be attacked include beet, cabbage, carrots, cucumber, eggplant, lima bean, lettuce, melon, okra, onion, parsnip, potato, pepper, pumpkin, radish, rhubarb, snap bean, Swiss chard, sweet potato, tomato, turnip, and watermelon. Other crops such as alfalfa, apple, clover, corn, cotton, peanut, pear, soybean, strawberry, sugarbeet, and sunflower also are reported as hosts. Numerous common weeds such as ield bindweed, Convolvulus arvensis; kochia, Kochia scoparia; lambsquarters, Che-nopodium album; purslane, Portulaca oleracea; plantain, Plantago spp. ; nightshade, Solanum spp. ; poverty-weed, Franseria discolor.; ragweed, Ambrosia spp.; redroot pigweed, Amaranthus retroflexus; and sorrel, Rumex spp. also support palestriped flea beetle adults. Suitable larval hosts are known to include plantain, ragweed, and lambsquarter (Hawley, 1922; Underhill, 1928), but there are probably many others. Despite the apparent wide host range, sugarbeet and bean are most frequently observed to be damaged. Weeds, especially bindweed and povertyweed, are often preferentially consumed, if they are available.

Natural Enemies. These insects are poorly studied, so the natural enemies are not well known. The parasitoids Microctonus epitricis Viereck (Hymenop-tera: Braconidae) and Howardula sp. (Nematoda: Allantonematidae) were recovered from palestriped flea beetle in Colorado (Capinera, 1979b). The wasp M. epitricis is often found associated with Phyllotreta and Epitrix spp. flea beetles (Loan 1967b); in Colorado it parasitized over 50% of palestriped flea beetles in the August collection, but generally the incidence of parasitism was negligible. Parasitized palestriped flea beetles also ate less foliage than unparasitized insects. Flea beetles, on average, supported 2.4 reproductive female nematodes per beetle. Infection by nematodes shortened beetle longevity by about three days. Nema-todes probably increase the rate of larval mortality, but this has not been studied in palestriped beetle. Elsey (1977a,b), Elsey and Pitts (1976) and Poinar

(1979) should be consulted for information on Howar-dula spp.

Life Cycle and Description. The number of generations per year for palestriped flea beetle is one in Canada and New York and two in Virginia. In California, the number is not known, but beetles are active from January through September. The adults of pales-triped flea beetle are active from mid-June until September in New York, whereas in Virginia the first generation of adults occurs from May through July, and the second generation from mid-July until September. Oviposition occurs from late July to late September in New York, where only a single generation occurs annually. In Virginia, where two generations occur, eggs are deposited from mid-May until mid-August for the first generation, and from late July until early September for the second generation. The insects overwinter as larvae in all locations.

  1. The egg of palestriped flea beetle is oval, and yellow. Eggs measure about 0.4 mm in width and 0.8 mm long. Eggs are deposited in the soil, adjacent to larval food plants, at a depth of 3.0-7.5 mm. The female may deposit the eggs singly, or in groups of up to eight, but 1-3 eggs per cluster seems to be normal for a single location. Beetles select several oviposi-tion sites for each oviposition event. Thus, 12-18 eggs are normally deposited per event, with 8 to 14 events observed during the life of each beetle. Total egg production per beetle averages 68-153, with fecundity of the spring generation tending to be lower. Incubation period of the eggs is 11-23 days.
  2. The larvae of palestriped flea beetles are elongate and slender and equipped with stout and black spines. Their color is white or yellowish, except for the reddish brown head. The abdomen bears an anal proleg, like most other flea beetle larvae, but also bears a large fleshy process dorsally at the tip of the abdomen. At hatching, young larvae measure about 1 mm long but attain a length of 8-11 mm at maturity. There are three instars, each requiring about six days for completion. Larvae consume the fibrous roots and the surface of larger roots. Occasionally, they tunnel into roots. Near the completion of the larval stage, larvae prepare a small cell in the soil, become shorter in length and thicker in diameter, and molt into the pupa. This nonfeeding prepupal stage lasts 3-4 days.
  3. The pupae are white and resemble the adult in form. Pupae measure 3.2-3.6 mm long. Duration of the pupal stage is about 8-21 days.
  4. The adult palestriped flea beetles measure 3.0-4.3 mm long. The most pronounced feature, and the basis for the common name, is the pair of pale yellow stripes along the back, one on each elytron. The stripe is broad, usually measuring one-third the width of the elytron. Although the background color of the elytron is usually dark, often black, in some specimens it is much paler, approaching yellow. In the latter case, the yellow band may not be evident. The thorax and abdomen are usually black or dark brown. The head is orange or reddish-brown. The hind femora are enlarged. (See color figures 3 and 116.)

Elongate flea beetle is poorly known. The immature stages have not been described. The adult is nearly identical to palestriped flea beetle. Palestriped flea beetle is quite variable in appearance, so there are no simple diagnostic characters to distinguish it from elongate flea beetle. In fact, further study may show that they are different forms of the same species. Blatchley (1910) and Smith (1970) suggested that these two species could be separated by the punctations on the gena (face), head, and pronotum; S. blanda is smooth to moderately punctate, whereas S. elongata is coarsely punctate.

The large size of Systena spp. is a good diagnostic character. Among the common crop-feeding flea beetles only Systena and Disonycha spp. exceed 3.5 mm in length.

The most comprehensive treatment of palestriped flea beetle was given by Underhill (1928). He distinguished S. blanda, palestriped flea beetle, from S. tae-niata Say, which he called the banded-flea beetle. Although these are now considered one species, Underhill (1928) suggested that the former overwinters as larvae while the latter passes the winter as adults. The biology of elongate flea beetle was reviewed by Smith (1970).

Damage

As is the case with most flea beetles, palestriped flea beetle larvae feed on roots. There are surprisingly few

Beetle Coleoptera

reports of larval feeding injury, possibly because weeds are preferred for oviposition. A notable exception is serious damage to young onions in Iowa, where not only roots but young bulbs were consumed (Drake and Harris, 1931). Sweet potato tubers also have been reported as injured.

The adults of palestriped flea beetle have been noted as serious pests, especially of seedling plants. Adults normally feed on the upper surface of foliage, making an irregular round feeding site. Beetles consume foliage at a rate of 0.3 sq cm per day (Capinera, 1978a). The lower epidermis, while left intact by the beetle, soon dies, forming a translucent membrane. Eventually, this membrane dries and drops from the leaf, leaving a hole. Leaves are often riddled with holes, with little more than veins remaining, where beetle density is high and availability of foliage is low. Such seedlings may perish, especially if water or temperature conditions are stressful for the plant. Beetles often aggregate, which leads to some plants being severely damaged, while others escape with minimal injury.

Management

  1. Beetles can be sampled with a sweep net or with traps. Yellow water-pan traps are very effective at capturing beetles relative to blue, green, black, red, orange, or white traps. Water-pan traps also are more effective than sticky traps (Capinera and Walmsley, 1978). If sticky traps are used, those positioned close to the soil (0.6 m above the soil) will catch more beetles than those that are elevated (1.2 m) (Capinera, 1980).
  2. Granular insecticide formulations, applied at planting time, often are used to protect seedlings from flea beetle larvae. Systemic materials also confer protection to seedlings, or aqueous materials may be applied as seedlings emerge. In most cases, it is only the seedlings that require protection.
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