Exotic Invasive Pests in Southern California Gardens

The following is a sampling of exotic, invasive pests found in Southern California gardens:

Ash Whitefly

  • Attacks fruit and shade trees
  • First found in California in the late 1980s
  • Caused defoliation, fruit loss, and tree death
  • Brought under control by a parasitic wasp from its native Middle East and Mediterranean

Black Scale

  • Periodic citrus pest and consistent issue for olives in San Jacinto Valley
  • Likely native to Africa, arrived in California before 1880
  • Infests a wide range of plants
  • Controlled to some extent by a natural enemy introduced in 1940, but still a persistent problem
  • Decreases fruit size and production when infestations are high

Eucalyptus Longhorned Borer

  • Discovered in Orange County in 1984
  • Destroys eucalyptus trees in larval stage by cutting off nutrient supply
  • Removal of dead trees costs $500–$5,000
  • Controlled via education, resistant species research, and parasite introduction

Formosan Subterranean Termite

  • Native to mainland China, introduced from Hawaii over 10 years ago
  • Colonies can exceed 1 million termites
  • Highly destructive—can render homes uninhabitable within two years
  • Strong presence in San Diego
  • Limited control success with insect growth regulators

Giant Whitefly

  • Likely native to Mexico
  • Attacks over 50 common ornamental plants
  • Causes defoliation, stunting, and potential plant death
  • Found in California, Texas, Louisiana, and Florida
  • Miniature parasitic wasps show promise in early field trials

Mediterranean Fruit Fly (Medfly)

  • First discovered in Southern California in 1975; reappeared in 1998
  • Affects at least 253 species of fruits, nuts, and vegetables
  • Females lay eggs under fruit skin; maggots rot the fruit
  • Researchers are studying behavior in Mediterranean regions for control strategies

Red Gum Lerp Psyllid

  • Australian native first detected in South El Monte in 1998
  • Rapidly spread across California, damaging eucalyptus trees
  • Feeds on plant fluids and can kill trees if untreated
  • Six Australian parasites being studied for natural control
  • Best prevention: proper watering, avoiding over-fertilizing and overpruning

Red Imported Fire Ant

  • Native to South America; major issue in the southern U.S.
  • Stings cause painful pustules, potential scarring, and in rare cases, death
  • Detected in Orange County in 1998
  • More than $1.1 billion spent annually in Texas on control efforts
  • Researchers studying insect behavior and insecticide options