Insects of the Month - Home Invaders - Roots Weevils and Maple Bugs

  Hort Snacks - September 2018
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 Maple Bugs / Box Elder Bugs | Root Weevils (Strawberry Root Weevils)

Each year, whether summer or fall, a number of insects will gather together and make attempts to enter buildings to shelter and/or overwinter. Most are not plant pests, and are merely nuisance insects that invade our residences. This article is meant to provide a bit more information on a couple of invaders that you might encounter.

Maple Bugs / Box Elder Bugs

Causal Agent: Boisea trivittata

Host plants: Various species of maple (Acer) and ash (Fraxinus); No agricultural crops


  • Adults are narrow, 14mm (1/2 inch) long insects, black/dark grey in colour, with red along the edges of their wings, and three distinctive stripes on their thorax (upper back/shoulders).
    • Stripes form a subtle X on the back when wings are folded flat (similar insects have a more distinct X)
  • Nymphs (immature stages) are bright red, with black wing buds
  • Nuisance pest
    • Stain surfaces when squished
    • Crushed bugs emit a foul odor
    • Poop can stain fabrics
Adult and various nymphal stages of Box Elder Bug
Photo by: William M. Ciesla, Forest Health Management International,

Life Cycle:
  • Adults emerge in the spring to lay eggs on the leaves and bark of host trees
  • Nymphs feed on seeds, foliage, twigs and fruit
    • Nymphs progress through several developmental stages until they become adults and begin reproducing immediately
    • Feeding on host trees does little damage
  • 2nd generation of adults will overwinter
  • Large numbers of nymphs and adults will be observed on the trunks of trees in early fall, just prior to migration
  • Insects seek a protected location to overwinter
    • Locations must be warm enough to be above freezing while they hibernate, but not so warm that they will expand all of their energy reserves and die
      • 4-10C (40-50F) is the preferred temperature range
    • Only adults have sufficient energy to survive the winter; the remainder of the insects (nymphs) will die
  • Block entrance points into buildings by caulking gaps and ensuring screens are intact
  • Vacuum up rogue invaders to avoid stains or odors
  • Spray groupings of mature/immature insects prior to migration with a mixture of water and dish soap (3-4% solution)
    • Contact with soapy solution will suffocate insects – insects not contacted with solution are unaffected
  • Removing host trees may remove breeding sites
Root Weevils (Strawberry root weevil)

Causal Agent: Otiorhynchus ovatus

Host plants: strawberries Description:
  • Adults are shiny, dark brown-black beetles, about inch in length, with blunt snouts and antennae that have elbows
    • Root weevils will drop to the ground when disturbed, do not fly and are nocturnal, emerging only at night to climb plants
  • Larvae are pale and legless
Strawberry Root Weevil adult
Photo by: Whitney Cranshaw, Colorado State University,

Life Cycle:
  • Root weevils overwinter as nearly fully grown larvae
  • Pupation is completed in the soil, with adults emerging in early summer
  • Eggs are laid near plant crowns
  • Larvae feed on host plant roots, whereas adults feed on leaves (resulting in leaf margin notching symptoms)
  • Adults often migrate into homes in late spring and late summer, perhaps to avoid hot, dry conditions
Management (around structures):
  • Block entrance points into structures
  • Vacuum up beetles found crawling around residences
  • Insecticidal treatments are generally unnecessary and/or ineffective – may be applied around the exterior of a structure
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on August 30, 2018.