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Aphids (Plant Lice)


  • Larvae: Nymphs hatch from the eggs in spring and start feeding on plants. All nymphs are female and are born already pregnant with the next generation. This is why aphid infestations are so hard to control. Several generations of larvae will grow up during a summer season.
  • Adult: Aphids are small, soft-bodied, insects about the size of a pinhead. They are generally green, but can vary in colour from yellow to pink to brown or black. They often live in large groups or colonies. When the host plant becomes overcrowded with larvae, aphids grow wings and move to other plants. In the fall, winged males appear to mate with females who lay eggs on perennial plants to over winter until next spring.

Identifying infestations:

  • Damaged plants: Aphids bite plants to draw sap, which in turn causes the plant to lose vigour, wilt, distort, or show spots. Most aphids feed on only one type of plant and do not bother others. For example, the woolly elm aphid causes the tree’s leaves to curl. This action ‘hides’ the aphid as it continues to feed from the leaf.
  • Sooty black droplets on surfaces: As they feed, aphids produce a sticky, sweet substance called honeydew that drips onto cars, sidewalks, porches etc. Black mould then grows on the droplets.
  • Ant colonies: Ants are often found where there is an aphid infestation since the ants ‘herd’ the aphids and feed on the honeydew produced.

IPM Toolkit:

  • Preventive tools: Not applicable
  • Physical tools:
    • Hose aphids off infested plants with a heavy spray of water. Hose again as needed.
    • Prune off heavily infested branches and destroy.
  • Biological tools:
    • Ladybird beetles, or Ladybugs, prey on aphids and can control small infestations. If you use chemical tools, you will kill these beneficial insects along with the aphids.
  • Chemical tools:
    • Insecticidal soap can control most aphid populations when applied according to label directions.