Coleoptera Chrysomelidae

Natural History

Distribution. Western black flea beetle is distributed widely in the western regions of the United States and Canada. It is particularly damaging along the western edge of the Great Plains, from Saskatchewan in the north to New Mexico in the south.

Host Plants. This insect has also been called the western cabbage flea beetle, which is a fair indication of its host preference. However, unlike many cruci-fer-feeding flea beetles, it will feed readily on other crops. Western black flea beetle is most damaging on mustard, radish, and turnip; but broccoli, cabbage, cauliflower, horseradish, kohlrabi, rutabaga, and watercress also are attacked. Among other vegetable crops, damage also has been reported on carrot, corn, beet, bean, lettuce, pea, potato, and tomato. Other economic plants injured include sugarbeet and nasturtium. Common weed hosts include pepperweed, Lepidium spp. and tansymustard, Descurainia pinnata. Feeding by larvae seems to be restricted to crucifers.

Natural Enemies. The principal natural enemies seem to be wasp and nematode parasites. Microctonus pussillae Muesebeck (Hymenoptera: Braconidae) is found throughout the summer months, but parasitism in excess of 16% has not been observed. A closely related parasitoid, M. punctulatae Loan and Wylie, also readily parasitizes this flea beetle under laboratory conditions, but levels of parasitism in the ield are unknown (Wylie, 1984). Nematodes, probably Howardula sp. (Nematoda: Allantonematidae) have been observed to be numerous in western cabbage flea beetle, but the only reported effect seems to reduce egg production by the beetles (Chittenden and Marsh, 1920). Birds also will consume flea beetles.

Life Cycle and Description. The number of generations per year is about three in Colorado, where the season of activity ranges from April until September. The duration of the life cycle is about 30 days. Adults overwinter in soil or under organic debris in northern climates. In warmer climates, beetles may remain active throughout the year.

  1. The eggs are deposited in soil near plants, with females each producing up to 250 eggs over a ten-week period. The oval eggs are light yellow, and measure about 0.5 mm long. Eggs hatch in 5-10 days.
  2. Young larvae feed on root hairs, while older larvae also feed on large roots. Larvae are whitish, except the head and anal plate that are brown. The larva bears an anal proleg, and eventually attains a length of about 5 mm. Duration of the larval stage is about 20-25 days.
  3. Mature larvae construct small pupal chambers in the soil, and spend two to ive days just before to pupation. Duration of pupation is about 10 days.
  4. Beetles are blackish with a shining surface, and have a metallic copper or bronze cast. The hind femora are enlarged. They measure 1.5-2.9 mm long.

The biology of western black flea beetle was outlined by Chittenden and Marsh (1920).

Damage

The principal form of damage is leaf feeding by adults. Beetles chew small holes in foliage, which can kill or impair the growth of seedling plants. Larvae also feed on the roots, reducing growth rates of plants. A more complete description of flea beetle injury can be found in the section on crucifer flea beetle, Phyllotreta cruciferae (Goeze).

Management

Management practices for this insect are similar to those recommended for crucifer flea beetle. The principal difference to consider is the wider host range of western black flea beetle. Not only may noncrucifer crops be damaged, but a wider variety of weeds will support beetle survival.

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