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Ministry of Agriculture, Food and Rural Affairs

Flea Beetles

Flea beetle Flea beetles on cauliflower Flea Beetle
Click to enlarge.

Beginner

Scientific Name
Phyllotreta sp.

All of the cruciferous crops grown in Ontario are susceptible to the damage caused by flea beetles. There are several species of flea beetles that attack crucifers. By far, the majority of these are crucifer flea beetles. Striped flea beetles make up about 10% of the population. They are capable of destroying enough foliage on seedlings to kill the plant. While all crucifers are attacked by these beetles, they prefer the non-waxy, ethnic crucifers.

Identification

  • Small (2– 3 mm, 1/12- 1/8 in.) shiny black beetles
  • Adults are active and jump when disturbed
  • Feeding damage consists of numerous “shot-holes,” 1– 5 mm (1/25- 1/5 in.) in diameter
  • At the seedling stage, flea beetle feeding can kill the plant

Often Confused With
Diamondback moth, Imported cabbageworm, and cabbage looper damage

Period of Activity
Adult flea beetles overwinter in leaf litter. They emerge and begin feeding on young plants in mid-May. Eggs are deposited near the roots of host plants throughout the spring and early summer. Larvae develop on the roots. In late July, adults emerge from the soil, feed and then seek hibernation sites in the fall. Cold and/or wet spring and early summer temperatures tend to keep damage pressure of this pest low. 

Scouting Notes
Inspect 25 randomly selected plants throughout the field. Since flea beetles are active and will jump away when disturbed, observations should be made when approaching the plant.  Record the number of beetles on each plant and divide by 25 to get an ‘average’ number of beetles per plant. A damage assessment of the shot-hole injury typical of adult feeding should also be taken into consideration due to the rapid movement of the flea beetle on a plant.

Thresholds
Up to the 6-leaf stage, plants can tolerate no more than 1 flea beetle per plant. After this stage, feeding will not interfere with plant growth. Feeding damage at later stages may have an impact on marketability and crop quality.

Advanced

Scientific Name
Phyllotreta sp.

All of the cruciferous crops grown in Ontario are susceptible to the damage caused by flea beetles. There are several species of flea beetles that attack crucifers. By far, the majority of these are crucifer flea beetles. Striped flea beetles make up about 10% of the population. They are capable of destroying enough foliage on seedlings to kill the plant. While all crucifers are attacked by these beetles, they prefer the non-waxy, ethnic crucifers.

Identification
The most common flea beetle attacking crucifers in Ontario is the crucifer flea beetle, Phyllotreta cruciferae. They are small, 2- 3 mm (1/12- 1/8 in.) long, shiny black beetles, with enlarged hind legs.  Adults are active and jump when disturbed. Striped flea beetles, Phyllotreta striolata are brownish-black with yellow stripes down their backs.

On cabbage, broccoli and cauliflower, flea beetles prefer the younger leaves. Typical damage consists of numerous 'shot-holes' 1- 5 mm (1/25- 1/5 in.) in diameter. Older feeding holes may be ringed with brown, dried leaf tissue, while fresh feeding holes have green edges. Numerous black or brown pellets of frass can be found scattered throughout the feeding area. Damage can be especially severe if the insects feed on the growing point of the plant. At the seedling stage, flea beetle feeding can kill the plant.

Often Confused With
Diamondback moth, Imported cabbageworm, and cabbage looper damage

Biology
Flea beetles in Ontario have one generation per year. Adult flea beetles overwinter in leaf litter and emerge early in the spring, around the middle of May. They feed initially on cruciferous weeds, volunteer crops and canola, and move in large numbers to cruciferous crops as they emerge. Eggs are deposited near or sometimes on the roots of host plants. Once hatched, larvae develop on the roots. Pre-pupal and pupal stages develop in the soil in an earthen cell. In late July, adults emerge from the soil, feed for a time and seek hibernation sites in the fall. The lifecycle from egg to adult may take as little as 7 weeks, making a second generation possible in some years.

Period of Activity
Adult flea beetles emerge early in the spring, around the middle of May and deposit eggs throughout the spring into early summer. The season’s newly emerged adults feed into the fall before seeking hibernation.

Weather plays a large role in flea beetle activity. Warm, dry conditions accelerate flea beetle development and the appearance of the new generation of adults, whereas cold spring and/or high rainfall in May or June tend to reduce the severity of damage and economic loss. 

Scouting Notes
Inspect 25 randomly selected plants throughout the field. Since flea beetles are active and will jump away when disturbed, observations should be made when approaching the plant.  Record the number of beetles on each plant and divide by 25 to get an ‘average’ number of beetles per plant. A damage assessment of the shot-hole injury typical of adult feeding should also be taken into consideration due to the rapid movement of the flea beetle on the plant.

Flea beetles tends to prefer to attack plants and foliage exposed to bright sunlight such as seedlings, isolated plants, or plants in widely spaced rows. Shade seems to inhibit their activity.

Thresholds
Up to the 6-leaf stage, plants can tolerate no more than 1 flea beetle per plant.  After this stage, the leaf surface is great enough that feeding will not interfere with plant growth. However, excessive feeding damage at any time leaves wounds where disease may enter. If black rot is present in the field, flea beetles may spread the disease. Control may be necessary because the threat of this disease is much greater than the threat of feeding damage.

Management Notes

  • Early plantings may be protected with row covers.
    Transplants are less susceptible to damage than direct-seeded crops.
  • Beetles tend to prefer specialty crucifers over traditional brassica crops.
  • In Ontario, flea beetles have been adequately controlled in cabbage, cauliflower and broccoli with the use of a trap crop, Indian mustard (Brassica juncea var. crispifolia). The trap crop should be planted up the drive rows.
  • The beetles are attracted to these plants when they are placed as far as 60 rows apart. They can be transplanted at the same time the crop is put in the field. 
  • It is not necessary to spray the trap rows, but uncontrolled feeding may reduce their effectiveness if flea beetles destroy too much of the foliage. 
  • Take care to ensure that the Indian mustard does not go to seed. 
  • The beetles are attracted to the Indian mustard even when the plant is mature and prefer this trap crop to the extent that they will usually not build up to threshold levels in the surrounding crop. 
  • Unfortunately in ethnic crucifer production systems the trap crop method has not been successful. The beetles appear to prefer the ethnic crucifers as much as the trap crop.