Disonycha mellicollis Say Coleoptera Chrysomelidae

Natural History

Distribution. Spinach flea beetle and yellow-necked flea beetle occur throughout the United States and Canada, east of the Rocky Mountains. Three-spotted flea beetle occupies the same area as the aforementioned species, but also occurs in British Columbia, Idaho, and Utah. These insects are native to North America.

Host Plants. These flea beetles are known principally as pests of the family Chenopodiaceae—beet, spinach, and Swiss chard. Therefore, it is not surprising that they damage sugarbeet, but they also are known to damage cabbage, canola, horseradish, lettuce, and radish on rare occasion. Weeds are their principal host, principally chickweed, Stellaria media; purslane, Portulaca spp.; lambsquarters, Chenopodium album; and pigweed, Amaranthus spp.

Natural Enemies. Little is known concerning the natural enemies of these beetles, although Chittenden (1899) reported that Medina barbata (Coquillett) (Diptera: Tachinidae) was a parasitoid of the adult spinach flea beetle, and Loan (1967a,b) found threespotted flea beetle to be attacked by Microctonus disonychae (Loan) (Hymenoptera: Braconidae).

Life Cycle and Description. These insects are poorly known, but spinach flea beetle has two generations annually in Maryland, with adults present throughout the year. The life cycle is reported to require 30-60 days. Apparently, these beetles overwinter in the adult stage and have been observed under loose bark of trees and other sheltered locations during the winter months. From the report of Beirne (1971) that adults are present in May and June and again in September and October, we might surmise that only one generation occurs in Canada. The life cycle of the other Disonycha flea beetles seems to be similar.

  1. The eggs of spinach flea beetle are laid in clusters of about 4-30 eggs, attached on end to leaves, stems, and sometimes on soil. They measure 1.251.50 mm long and 0.40-0.57 mm wide, and are orange in color. The eggs of threespotted flea beetle seem to be undescribed, but they likely are similar to spinach flea beetle. Yellownecked flea beetle is known to deposit clusters of eggs in a manner similar to spinach flea beetle, but they are somewhat unusual in that they are red in color. Eggs hatch in 4-10 days, the larvae escaping by chewing a slit in the side of the egg.
  2. The larvae are normally grayish, though sometimes purplish when feeding on beet foliage. The head is darker, and the body is well-equipped with short and stout spines. Initially measuring about 1.8 mm long, the larvae reach 8-9 mm at maturity. Larvae require 10-30 days to complete their development.
  3. Larvae drop to the soil to form a small pupation cell. Pupae resemble adults, but are grayish in color. Pupation requires 10-14 days.
  4. Adults of Disonycha are fairly large for flea beetles, measuring 5-6 mm long. Among the common crop-infesting flea beetles, only Systena spp. approach Disonycha in size. Their elytra are shiny black, sometimes tinged with blue or green. The prothorax is yellow or red. Threespotted flea beetle can be distinguished from the other species by the three black spots on the thorax. (See color figure 117.) Yellownecked flea beetle can be distinguished from spinach flea beetle by the color of the femora: in the former the femora are entirely yellow, whereas in the latter they are partly blue or green. Females produce an estimated 100-300 eggs.

The biology of spinach flea beetle was provided by Chittenden (1899), that of threespotted flea beetle

Adult spinach flea beetle.
Pictures Spinach Flea Beetles
Adult threespotted flea beetle.

by Maxson (1948), and of yellownecked flea beetle by Chittenden (1912b).

Damage

The larvae of Disonycha flea beetles differ from the more common genera in that they feed on foliage rather than roots. They tend initially to be gregarious, but this habit dissipates as they mature. They usually feed on the underside of the leaves, initially feeding only partially through the leaf tissue, but eventually creating holes. Adults similarly feed on the leaf tissue, skeletonizing the foliage. Generally, these flea beetles are not considered serious pests.

Management

Because weeds are often important in the biology of these insects, an important element of insect control is weed suppression. Should the insects require suppression, foliar insecticides provide quick relief. The beetles do not seem to overwinter in the soil, so covering crops with netting or row cover material will prevent damage in the spring.

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Responses

  • settimio
    How to get rid of the flea beetles on my spinach and swiss chard?
    6 years ago

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