Are All Flea Beetles the Same?
Crucifer Flea Beetle Versus Leafy Spurge Flea Beetles

E-1274, July 2005

Denise L. Olson, Assistant Professor, Department of Entomology
Janet J. Knodel, Extension Crop Protection Specialist, NCREC, NDSU

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Flea beetles have enlarged hind legs that they use to jump quickly when disturbed.

"FLEA BEETLE" is a common name describing many species of beetles that use their enlarged hind legs to jump quickly when disturbed. The adults feed on the leaves of their host plants. Heavily fed-on leaves have a shot-hole appearance. The larvae (wormlike immature stage) usually feed on the roots of the same host plants as adults.

Crucifer flea beetle is an exotic insect pest.

Common flea beetles that occur in North Dakota include the crucifer flea beetle (Phyllotreata cruciferae) and the leafy spurge flea beetles (Aphthona species). The crucifer flea beetle is a non-native insect pest that accidentally was introduced into North America during the 1920s. Phyllotreata cruciferae now can be found across southern Canada and the northern Great Plains states of the United States. The leafy spurge flea beetles are non-native biological control agents and were introduced for spurge control beginning in the mid-1980s. These biological control agents have been released in the south-central provinces of Canada and in the Upper Great Plains and Midwest states of the United States. Although P. cruciferae and Aphthona species are both known as flea beetles and do look similar, they differ in their description, life cycle and preference of host plants.

Leafy spurge flea beetle species are introduced biological control agents.

Crucifer Flea Beetle

Description

The adult is a small (about 1/32 to 1/8 inch), oval-shaped, bluish-black beetle with numerous dimples on the wing covers (Figure 1). The whitish larva is wormlike and approximatley 1/8-inch in size, with tiny legs and a brown head.

Figure 1. Crucifer flea beetle. (Click here for a 51KB color photo.)

Life Cycle

The crucifer flea beetle has one generation per year. Adult flea beetles overwinter in leaf litter of shelterbelts and grassy areas. They emerge from the overwintering sites during early spring as temperatures reach up to 57 F.

Overwintered adults feed on seedling cruciferous host plants. Summer adults feed on the pods of canola, mustard and cruciferous weeds.

Volunteer canola and wild mustard are usually the first available host plants, with the beetles moving into the new canola fields as the crop emerges. Overwintered adults are usually active in the fields until late June, feeding on the foliage and depositing their eggs in the soil. The larvae can be found in the root zone of host plants during June and July. The pupal stage occurs from early to mid-July. The new generation, or summer adults, are present from late July to early September. They can be found feeding on the pods of canola, mustard, and cruciferous weeds. The summer generation will move to overwintering sites in early fall.

Host Plants

The crucifer flea beetle is an economic pest of oilseed Brassica (canola) and has a narrow host range restricted to plants in these families: Capparidaceae - clammyweed and spider plant; Tropaeolaceae - nasturtium; Limnanthaceae - meadow-foam; Cruciferae - candytuft, cow-cress, poor-mans pepper, shepherds-purse, radish, charlock, turnip, cabbage, cauliflower, broccoli, hedge-mustard, common wintercress and honesty. The crucifer flea beetle is known to be attracted to mustard oils. Mustard oils are common components among the plants selected by the crucifer beetle, suggesting that these compounds are the basis for host plant selection by this flea beetle species.

Feeding Injury

The overwintered adults cause the injury to their host plants. In the spring, they feed on the seedlings, producing pits in the tissue of the cotyledons and first true leaves. As the leaf tissue dies around the pits, the cotyledons and leaves appear shot-holed (Figure 2). Plant stand and plant growth can be reduced and maturity delayed when the crucifer flea beetle feeds on the seedling stage of its host plants. The larvae feed on secondary roots of host plants but this feeding has a negligible effect on plant vigor or yield. After "mid-July, summer adults feed on the developing pods or seeds (Figure 3). The host plant can have poor seed fill, premature pod drying, shriveled seed, or pod shattering from these infestations.

Figure 2. Crucifer flea beetle feeding injury. (Click here for a 123KB color photo.)

Figure 3. Adult crucifer flea beetles feeding on mature stems and pods of canola. (Click here for a 182KB color photo.)

Leafy Spurge Flea Beetle

Six Aphthona flea beetle species were released in North Dakota for biological control of leafy spurge. Of these six species, the black flea beetle, A. lacertosa (Figure 4), and the brown flea beetle, A. nigriscutis (Figure 5), are the two species that have been the most successful and most commonly are redistributed to areas infested with leafy spurge. The first release of A. lacertosa in North Dakota was in 1988 and A. nigriscutis first was released in 1989. These two species have reduced leafy spurge to a nonweed problem in some areas of North Dakota.

Figure 4. A. lacertosa. (Click here for a 101KB color photo.)

Figure 5. A. nigriscutis. (Click here for a 57KB color photo.)

Aphthona lacertosa and A. nigristus have been the most successful against leafy spurge.

Description

Aphthona flea beetles appear shiny or "polished" rather than being "dimpled" as in the economically important crucifer flea beetle, and they are approximately 0.10 inches long. The brown flea beetle, A. nigriscutis, has a clearly visible dark brown to black triangular mark directly below the thorax and between each wing cover (Figure 5). The black flea beetle, Aphthona lacertosa, is actually metallic blue and the enlarged segment of the hindlegs is yellow to brown (Figures 4 and 6).

Figure 6. A. lacertosa. (Click here for a 63KB color photo.)

Life Cycle

The leafy spurge flea beetles have one generation per year. However, they overwinter as third instar larvae (Figure 7) in the soil near the spurge roots. The larvae resume feeding on the spurge roots as the soil temperature exceeds 45 F in April and May. Root feeding continues into late May and early June, at which time they enter the pupal stage. The adults emerge from the soil during late spring into early summer and feed on the spurge vegetation and lay eggs in the cracks of the soil near the base of the leafy spurge stems. Aphthona lacertosa and A. nigriscutis adults live for about 1-1/2 months in hot and dry conditions, and up to two months in cooler, wetter conditions. The newly emerged larvae tunnel into the soil searching for the leafy spurge fibrous roots (feeder roots) near the soil surface. Second and third instar larvae (Figure 6) feed on the larger roots and root buds. The third instar larvae move deeper into the soil to overwinter as the soil temperature falls below 45 F.

Figure 7. Aphthona flea beetle larva. (Click here for a 110KB color photo.)

The leafy spurge flea beetle larvae overwinter in the soil near the spurge roots.

Host Plants

Both leafy spurge flea beetles feed exclusively on plants in the family Euphorbiaceae (spurges). Variation in plant structure and habitat of the spurge species recorded as hosts suggest that secondary compounds, possibly latex, are important in this strong relationship between spurges and their flea beetles. Before releasing the Aphthona flea beetles into the United States, host specificity tests were conducted using several economic plants including canola, beet, corn, potato, sweet potato, carrot, rhubarb, and a perennial herb. None of these crops serve as hosts for the Aphthona species released into the United States.

Feeding Injury

The adult spurge flea beetles feed on the foliage of leafy spurge (Figure 8). However, it is the feeding by the larvae on the root system that causes the greatest damage to spurge and results in stand reduction. First instar larvae feed on the fine feeder roots, which reduces water and nutrient uptake. Second and third instar larvae reduce the energy storage tissue of the root crown by feeding on the larger roots. In addition, the plant becomes more susceptible to herbicides and infection from soil-borne pathogens after the larvae have injured the root system.

Figure 8. Adult Aphthona on spurge foilage. (Click here for a 63KB color photo.)

Photograph credits:

Figure 1, 4, 5, 6 -- Gerald Fauske, Department of Entomology, NDSU
Figure 2, 3 -- Janet Knodel
Figure 7 -- Denise Olson
Figure 8, Cover (Aphthona lacertosa) -- USDA-APHIS-PPQ
Cover (Phyllotreata cruciferae) -- Lloyd Harris, Regina, SK, Canada

For more information on this and other topics, see: www.ag.ndsu.edu

E-1274, July 2005