The term Flea beetle is a generic name applied to many species of small jumping beetles commonly seen early in the gardening season. Some species are general feeders while others have a more restricted host range. All flea beetle life stages are completed underground. Only the adults are commonly seen by gardeners and vegetable producers.
Flea beetles may be somewhat elongate to oval in shape, and vary in color, pattern, and size. For instance, potato flea beetles (Epitrix cucumeris) tend to be more oval, blackish, and about 1/16" long.
Striped flea beetles (Phyllotreta striolata) are more elongate and dark with yellowish crooked stripes, and measure about 1/12" long.
Spinach flea beetles (Disonycha xanthomelaena) are both oval and elongate. They have a black head, antennae and legs. The collar behind the head is yellow to yellowish-orange. Wing covers have blackish-blue luster. They approach 1/5" in body length.
With most species of flea beetle, the adults over winter underground or beneath plant debris. During April and May, they become active, mate, and deposit eggs.
Egg laying varies depending upon species. Some deposit individual eggs while others deposit them in clusters. Egg sites may be in soil, on leaves, on leaf petioles, or within holes chewed into stems.
Eggs typically hatch in 10 days. Larval and pupal development take place during the summer. "New" adults emerge and feed during late summer and fall before seeking over wintering sites.
Adults generally over winter in fields of host plants, and move to weeds and plant beds in early spring and later to transplanted vegetables and garden plants. They are most destructive to young plants. There are 3 or more generations per year.
Larvae feeding on underground portions of plants may result in decreased plant vigor. In some instances, crops produced underground may be scarred because of larval feeding activities.
Large populations of feeding adults can devastate plantings, especially if the planting is in the seedling stage. Small circular gouges taken mainly from bottom leaf surfaces cause plants to take on a peppered or shot holed appearance. Corn flea beetles feed between veins on upper leaf surfaces, resulting in a silvery and streaked appearance.
Flea beetles also transmit Stewart's Bacterial Wilt to corn.
Management is seldom required for this pest; however, there are a few tactics that can help reduce the likelihood of problems. Agricultural fields kept free of weeds in and around the field are less likely to be injured by the pest. Avoid early planting dates that slow seedling development. In cases where early planting is necessary, the field should be watched closely for developing infestations (from emergence to the fourth leaf stage), and a rescue insecticide treatment can be applied if needed. It is not economical to apply a preventative treatment just for this pest.
However, if a soil insecticide will be applied for other more common pests, then select a material also effective against the flea beetle to prevent injury.
In the home landscape garden, insecticides containing carbaryl (Sevin), spinosad, bifenthrin and permethrin can provide fairly good control for about a week. However, to protect seedlings, applications usually must be reapplied. The plants produce continuous new growth and the highly mobile beetles may rapidly reinvade plantings. As with all pesticides, carefully read and follow all label directions. Pay particular attention to ensure that any flea beetle insecticides being considered are properly registered for use on the crop.
Diatomaceous earth is one of the more effective repellents, applied as a dry powder to the plants. Horticultural oils and some neem insecticides also have some repellent effect on this insect.