Pest profile

Allium Leafminer

Phytomyza gymnostoma · Diptera: Agromyzidae[3]

Allium leafminer is an invasive fly whose larvae feed in the leaves of onions, leeks, chives and garlic and burrow into the bulb, stunting plants.[1]

No licensed photo of this species is available yet; the identification notes below describe what to look for.

How to identify it

  • The first sign is a straight line of round white dots on allium leaves, where females punctured them to feed and lay eggs.[2]
  • Adults have an orange patch on the head and fold their wings flat over the back; they often sit at leaf tips in the morning.[2]

Where it lives

First found in Pennsylvania in Lancaster County in 2015, it spread to nearby states and is probably throughout Pennsylvania.[1]

US map: public records from 9 states since 1990 (GBIF).

Biology and life cycle

There are two generations a year: adults fly for 4 to 5 weeks in spring and again in fall.[2]

It overwinters as a pupa in leaf tissue or nearby soil, and summer pupae rest until fall.[2]

Wild onions and green onions or leeks are good places to check for its leaf punctures.[1][2]

Damage and signs

  • Larvae feed on leaf tissue and burrow into the bulb, stunting growth and making leaves and bulbs unpalatable.[1]

Health risk

It feeds on plants; Penn State Extension mentions no risk to people.[1]

Control

Prevention

Plant garlic as late in fall as possible, around November 1 in southeastern Pennsylvania, so plants are too small for fall egg laying.[1]

Keep them out

Cover alliums with floating row cover during adult flight, after checking that flies aren't already active underneath; leave it on 4 to 6 weeks.[1][2]

Pesticides

Control is only needed during and just after adult flight; for organic plantings, Penn State lists two sprays of spinosad mixed with soap.[2]

Common questions

What are the lines of white dots on my onion leaves?
They're likely punctures made by female allium leafminers feeding and laying eggs.[2]
How can I protect garlic from allium leafminer?
Plant late in fall to dodge the fall flight, then use floating row cover during the spring flight.[1]

Sources

  1. Penn State Extension, “Plant Garlic Late to Avoid Allium Leafminer.” extension.psu.edu/plant-garlic-late-to-avoid-allium-leafminer (accessed 2026-10-06)
  2. Penn State Extension, “Allium Leafminer Emerging Now in Southeastern PA.” extension.psu.edu/allium-leafminer-emerging-now-in-southeastern-pa (accessed 2026-10-06)
  3. iNaturalist, “Phytomyza gymnostoma taxon page (order and family).” www.inaturalist.org/taxa/779741 (accessed 2026-10-06)

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