Bug FAQKnapweed Root Moth
Agapeta zoegana · Order: Lepidoptera · Family: Tortricidae
Also called: Sulfur knapweed root moth, sulphur knapweed moth
The knapweed root moth is a small, bright-yellow moth about 11 mm long, with brown markings on its wings. Its larvae mine the roots of spotted and diffuse knapweed, and the species is used to help control these invasive weeds.
Source: Wikipedia
How to recognize it
Adults are bright yellow with brown areas on the wings, including a small subdorsal spot and a large terminal blotch.
Source: Wikipedia
Size
The moth measures about 11 mm in length.
Source: Wikipedia
How to get rid of it
The moth is released as a biological control agent against invasive knapweeds, especially spotted and diffuse knapweed. It helps reduce the spread of these weeds where mechanical or chemical control is impractical.
Source: Wikipedia
What it eats
Larvae are root miners that tunnel through the cortex of knapweed roots as they feed.
Source: Wikipedia
Life cycle
Adults live only a few days, during which females lay eggs on stems and leaves. They fly from May to August at dusk and are attracted to light.
Source: Wikipedia
When you see it
Flight period is May through August, mainly at dusk.
Source: Wikipedia
Where it comes from
The species is native to Eurasia.
Source: Wikipedia
Lookalikes
It is also called the sulphur knapweed moth or yellow-winged knapweed root moth.
Source: Wikipedia
Where it is found in the US
Recorded in 9 of 51 states and DC. Most records: Montana, Washington, Idaho, Oregon, Wyoming, Minnesota, Colorado, Arizona.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: introduced in United States; introduced in Canada. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
What does the knapweed root moth look like?
It is a bright-yellow moth about 11 mm long with brown spots and a large terminal blotch on its wings.
Source: Wikipedia
When are adult knapweed root moths active?
Adults fly from May to August, mainly at dusk, and are attracted to lights.
Source: Wikipedia
Is the knapweed root moth used for weed control?
Yes, it is released to biologically control invasive knapweeds like spotted and diffuse knapweed.
Source: Wikipedia
Same family (Tortricidae)
Oblique-banded Leafroller MothChoristoneura rosaceanaDamages trees, gardens or crops
Garden TortrixClepsis peritanaDamages trees, gardens or crops
Common MarbleSyricoris lacunanaDamages trees, gardens or crops
Red-banded Leafroller MothArgyrotaenia velutinanaDamages trees, gardens or crops
Light Brown Apple MothEpiphyas postvittanaDamages trees, gardens or crops
Filbertworm MothCydia latiferreanaDamages trees, gardens or cropsSources
- Wikipedia: https://en.wikipedia.org/wiki/Agapeta_zoegana
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-22 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.