Phyllotreta zimmermanni Crotch Coleoptera Chrysomelidae

Natural History

Distribution. Zimmermann's flea beetle is widespread in North America, and is known from nearly all states and provinces. However, it is most frequently found in the northeastern and midwestern states. Its abundance is reported to have diminished with the introduction from Europe of crucifer flea beetle, Phyllotreta cruciferae (Goeze), and striped flea beetle, Phyllotreta striolata (Fabricius), presumably owing to competition.

Host Plants. This beetle feeds principally on cru-cifers, including such vegetables as broccoli, cabbage, collards, mustard, radish, turnip, and watercress. The adults sometimes feed on other plants, however, and have occasionally been observed feeding on alfalfa, clover, horseradish, peach, sunflower, tobacco, and wheat. Weeds serving as suitable hosts are black mustard, Brassica nigra; Virginia pepperweed, Lepidium virginicum; shepherdspurse, Capsella bursa-pastoris; yellow rocket, Barbarea vulgaris; and especially common hop, Humulus lupulus; and pepperweed, Lepidium spp. Larval hosts are reported as watercress, pepper-weed, and infrequently rock cress, Arabis sp.

Natural Enemies. A common flea beetle parasi-toid, Microctonus vittatae Muesebeck (Hymenoptera: Braconidae), attacks Zimmermann's flea beetle and attains levels of parasitism of 60-70% (Loan, 1967b). The parasitoid is subject to hyperparasitism by Mesochorus phyllotreta Jourdheuil (Hymenoptera: Ichneumonidae), which diminishes the effectiveness of the primary parasitoid in regulating flea beetle abundance. A nematode, Howardula sp. (Nematoda: Allantonematidae) also was reported to parasitize this beetle (Elsey, 1977a).

Life Cycle and Description. Apparently there is only a single generation per year, though the complete life cycle requires about 30 days. Adults are the overwintering stage, and become active early in the spring, which is March in most of the United States, but April or May in Canada.

  1. Beetles deposit their eggs on the upper surface of foliage along the midvein. They were reported by Riley (1884) to be white and elongate, and measure only 0.02 mm long, but this measurement is likely an error; 0.2 mm is more probable.
  2. The larvae are dark orange, with darker spots, and a head that is nearly black. They attain a length of about 5 mm at maturity. The larvae burrow into the foliage and feed as leaf miners between the upper and lower epidermis. This feeding habit is unusual among crop-feeding flea beetles, although several weed-feeding species also are leaf miners. In Missouri, the larvae are very abundant during May and June (Riley, 1884). The larvae may leave their mine and form another in a more suitable location, including another leaf.
  3. Pupation occurs in the soil. The pupa seems to be undescribed, but likely is very similar to that of crucifer flea beetle, Phyllotreta cruciferae (Goeze).
  4. Beetles are black or blackish, with a straw-yellow irregular band running the length of each elytron. They greatly resemble striped flea beetle and western striped flea beetle. These flea beetles are most easily distinguished by the size of the fifth antennal segment of males. In western striped flea beetle, Phyllotreta ramosa (Crotch), antennal segments 4-6 are nearly the same size. In striped flea beetle, the fifth segment is wider and longer than adjacent segments, about twice the length of the sixth segment. In males of Zimmermann's flea beetle, the fifth antennal segment is even more enlarged, about three times the length of the sixth segment. Zimmermann's flea beetle measures 2.0-3.0 mm long and averages larger than the other two species.

The biology of Zimmermann's flea beetle was outlined by Riley (1884), Chittenden (1927), and Smith (1985).

Damage

Although larvae are leaf miners, they generally confine to their feeding activity to weeds, and so cause no

Phyllotreta Striolata
Adult Zimmermann's flea beetle.

economic loss to crops. Adults can sometimes become abundant, and in early spring they can be damaging to seedling plants. Adults eat small holes in the foliage, sometimes completely skeletonizing leaves, leading to the death of young plants.

Management

Management of adult flea beetles was discussed in detail under crucifer flea beetle, which should serve as a guide for Zimmermann's flea beetle control. Unlike crucifer flea beetle, however, larval control is not an issue.

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