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.
The biology of spinach flea beetle was provided by Chittenden (1899), that of threespotted flea beetle
by Maxson (1948), and of yellownecked flea beetle by Chittenden (1912b).
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.
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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