POTATO and TUBER FLEA BEETLES
There are many small leaf feeding beetles called flea beetles because of their well-developed hind legs that allow them to jump like fleas. In potato, the principle flea beetles are in the genus Epitrix and are considered a minor pests. Of these the potato flea beetle (E. subcritita) and the tuber flea beetle (E. tuberis) are the most economically important. They look very much a like and are hard to distinguish; however they are geographically separate. The potato flea beetle is found from mid-Nebraska east to Maine and along the Atlantic Coast south to the Carolinas. The tuber flea beetle is found from western Nebraska and Colorado west through the inter-mountain States to the Pacific Coast up through the Pacific Northwest.
Adults have an oval body, and their color is shiny green to brown to black. Their hind legs are enlarged for jumping. They are about 1/16 inch long.
Eggs are white and oval. They are deposited in soil crack near the surface and are not seen due to their very small size.
Larvae are elongated soft-bodied grubs about a quarter to a third inch long. Their body is whitish with a yellowish or light brown head. They have six short legs.
Pupa are rarely seen as they form several inches in the soil.
Flea beetle adult, flea beetle leaf damage, flea beetle tuber damage (from left)
Adult flea beetles overwinter near where they emerged. They will overwinter in plant debris and weed hosts. The potato and tuber flea beetles usually will burrow into the ground a few inches but may go as deep as a foot and a half. In light soils, many of the adults will go into a hibernation period below normal plowing depth. Adults emerge when the temperature reaches 50oF, between May to early June in the North and earlier in the South, and begin feeding on weeds or Solanaceous bedding plants such as tomato. When potato plants have emerged, many will fly into the potato field and the adults begin feeding on the foliage. Adults mate and eggs are deposited on the soil surface and in its cracks near potato plants. After about 10 days, larvae hatch. The early generations’ larvae feed on roots and underground stems, and sometimes on growing tubers. Mature larvae leave the potato structure and dig a small smooth earthen chamber in which they pupate. Pupation is short; newly-formed adults are soft-shelled and crawl to the surface where their shell hardens and darkens. The cycle normally takes four to six weeks but can be delayed to nine weeks under unfavorable conditions. Normally, there are one to four generations per season depending on locale.
Damage by flea beetles is of two major types, on foliage and on tubers. The principle damage by the potato flea beetle is foliar while the economic damage by the tuber flea beetle is to the tubers to be harvested.
Damage to foliage is from feeding adults of all flea beetles and are small round holes scattered in the leaf blade giving them a “shot hole” or seive-like appearance. A slight chlorosis, yellowing, may occur around the holes. This injury is not economic to treat for and rarely defoliation occurs. Usually only the potato flea beetle, found in the eastern half of North America, will occasionally cause enough foliar injury to be economically important. When the rare severe infestation occurs, plants can defoliate, and tubers can become remain small and become deformed.
The last generation of larvae cause the most economic damage by feeding on mature tubers. Their feeding results in tubers with narrow, straight tunnels about 1/32 inch wide along the perimeter of the tuber. The tunnels are usually shallow but can extend as much as 1/2 inch deep. The tuber flea beetle, found in the western half of the continent, is especially damaging as they scar the tuber badly and also drill deeper. So, besides holes, small raised bumps also may appear on the tuber surface. Extensive tuber feeding can make the tuber unmarketable for the fresh and processing markets but have no effect on seed tuber vigor. However, there also are reports that the tuber holes can act as entryways for pathogenic bacteria such as soft rot and fungi such as dry rot making the tubers unsuitable for seed as well.
Flea beetle infestation are sporadic and unpredictable; economic thresholds are not known. Since flea beetles tend to stay around potato plants, crop rotation may play a key role. Controlling weeds around and in potato fields is a key part of holding down flea beetle populations. Common, soil-applied systemic insecticides work well in controlling adults. Foliar products used for other pests such as Colorado potato beetle and green peach aphid work well against flea beetle adults. Treatment for larvae are not available.
Adult - oval; shiny green to black; large hind legs; 1/16 inch
Larvae - thread-like grubs; whitish; up to 1/3 inch
Overwinters as adults in debris or hibernate
One to four generations per season
Generation is 4 to 6 weeks up to 9 weeks
Foliage has shot-hole appearance
Tubers have narrow tunnels and possibly scars
Systemic soil insecticides at planting
Foliar insecticides when used for other pests