Pest profile

Ash Whitefly

Siphoninus phillyreae · Hemiptera: Aleyrodidae[2]

The ash whitefly is an invasive whitefly found in Oregon by 2014; clouds of it appear in late summer and fall on ash, pear, hawthorn and many other trees.[1]

Ash whitefly nymphs and pupal cases covered in white wax tufts on a leaf underside
Ash whitefly nymphs and pupal cases covered in white wax tufts on a leaf underside. (c) Grey Smith, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are about 0.05 inch long, with translucent white wings that may show the yellow body through them.[1]
  • Nymphs are translucent and covered with tufts of white wax, and the waxy pupal cases ooze sticky honeydew.[1]
  • Infested leaves carry a sticky mess of eggs, waxy nymphs, pupal cases and honeydew.[1]

Where it lives

Detected in California in 1988, it was found in Oregon by 2014, and clouds of it appear in the Willamette Valley in late summer and fall.[1]

US map: public records from 7 states since 1990 (GBIF).

Biology and life cycle

Females lay eggs under leaves; nymphs settle and feed on sap, then pupate and emerge as winged adults.[1]

Adults live 30 to 60 days, with several generations a year.[1]

Adults leave summer hosts such as ash, pear and hawthorn to overwinter and breed on evergreen hosts.[1]

Damage and signs

  • Heavy feeding can defoliate trees, cause early fruit drop and, in severe infestations, kill the host plant.[1]

Health risk

It feeds on plants; the PNW Insect Management Handbook mentions no risk to people.[1]

Control

Prevention

Watch for clouds of tiny whiteflies, or sticky honeydew and sooty mold under infested leaves.[1]

Traps and physical control

Strong streams of water aimed at leaf undersides can dislodge or injure the various stages; sticky traps and screening give some protection.[1]

Biological control

In California the parasitic wasp Encarsia inaron parasitized 80 to 98 percent of ash whitefly nymphs, and pesticides were avoided to let it build up.[1]

Common questions

What are the clouds of tiny white insects around my ash tree in fall?
They may be ash whiteflies, which appear in clouds in late summer and autumn.[1]
Is there a natural control for ash whitefly?
Yes. The parasitic wasp Encarsia inaron was the most successful control in California and Florida.[1]

Sources

  1. Pacific Northwest Pest Management Handbooks (OSU, WSU, University of Idaho), “Emerging Insect Pests in the Pacific Northwest: Ash whitefly (2015).” pnwhandbooks.org/insect/emerging-insect-pests/emerging-insect/ash-whitefly-2015 (accessed 2026-10-06)
  2. iNaturalist, “Siphoninus phillyreae taxon page (order and family).” www.inaturalist.org/taxa/397210 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.