Operational Field Guide: Agapeta zoegana - BIOLOGY


Order: Cochylidae

Common name: sulphur knapweed moth, yellow-winged knapweed root moth


GENERATIONS PER YEAR: generally one in North America (two to several in Europe)

ADULT STAGE: Adults are 1-2 cm long moths with bright yellow bodies and brown patterns on the wings (Photo 1). Females have a larger body than do males, with a more rounded abdomen. Males have a pair of clasping pincers at the end of the abdomen. Adults emerge from the overwintering generation from mid-June to late-August with emergence timing linked to habitat location and weather patterns. Mating begins almost immediately with eggs being laid throughout the 10- to 14 day life span on lower leaves, especially the rosette. Eggs are oval in shape and somewhat flattened (0.75 mm long and 0.45 mm wide). They are whitish when deposited and turn progressively reddish within 3-4 days.

LARVAL STAGE: Larvae hatch 7-10 days after the eggs are laid and migrate into the root crown. Larvae mine the root tissue just below the outer surface, leaving spiral trails covered by a thin, whitish web. There are six larval instars. Most larval growth occurs throughout the fall before the larvae become dormant for the winter.

PUPAL STAGE: Pupation occurs inside the web near the root crown in late spring/early summer approximately two weeks prior to emergence.

DISPERSAL METHOD: Adults are airborne and disperse by flying. Wind may have an effect on dispersal patterns. Larvae have been found to migrate through the soil to new roots to complete life cycles but as a dispersal method this is not significant.

Photo 1: Agapeta zoegana (adult)

ag1.jpg (152217 bytes)

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