 
Left: Agapeta zoegana. V.Farquhar
Right: A. zoegana larva on knapweed root. R.Richard.
Agapeta zoegana
(Lepidoptera: Cochylidae)
by Ronald Lang, USDA-APHIS-PPQ, Forestry Sciences Lab, Montana State
University, Bozeman, MT 59717-0278.
Agapeta zoegana , a root boring moth from Europe, was first released
in the United States in 1984. Its release is part of a program to introduce
a complex of spotted and diffuse knapweed enemies to help control these
natives of Eastern Europe and Asia. In North America spotted and diffuse
knapweed are efficient competitors and since being introduced around the
turn of the century have spread throughout the northern tier of states
and as far south as Nebraska and Virginia. They favor disturbed sites
and overgrazed rangelands and cause a reduction of forage for cattle of
up to 100% in infested areas. Spotted knapweed and diffuse knapweed also
prosper on grasslands and riparian sites and displace native vegetation
in these habitats.
Although knapweed can be controlled  by
extensive cultivation or herbicide application, its existence on stream
banks and rough terrain and the typically expansive areas of infestation
make these methods impractical and/or economically unfeasible. Therefore,
an integrated pest management approach is being sought to help in controlling
this weed.
A. zoegana has been released in Arizona, California, Colorado,
Idaho, Minnesota, Montana, Nebraska, Nevada, North Dakota, Oregon, South
Dakota, Utah, Washington, Wisconsin, and Wyoming. The moth has established
in these states.
Appearance
A. zoegana is a small bright yellow moth, 10 mm in length, with
brown wing bands. The adults may be found resting vertically on the knapweed
stems or under the leaves. They have the appearance of dead or dying knapweed
leaves.
Habitat
Spotted and diffuse knapweed-infested areas.
Pests Attacked
A. zoegana is considered host-specific to spotted and diffuse
knapweed. It has been tested on fifty-one plant species including closely
related native species and species of economic importance such as safflower.
Life Cycle
Adult moths emerge from knapweed roots in early July through early September.
Mating takes place within twenty-four hours after emergence and the mated
female begins laying eggs the next day. The eggs are laid in the stem
crevices and on the leaves of the spotted and diffuse knapweed plants.
The larvae hatch from the eggs in seven to ten days and move immediately
to the root crown and mine into the root.
Larvae are capable of killing small rosettes and then moving a few centimeters
to another knapweed plant to feed. The larvae pupate in the root in midsummer.
Adults live from eleven to fourteen days with each female laying from
twenty-one to seventy-eight eggs in her lifetime. The moths are strong
fliers and will invade new knapweed patches.
Pesticide susceptibility
Not yet known.
Commercial availability
In some states, A. zoegana adults may be obtained at no cost from
state weed management agencies. Several commercial suppliers can also
provide A. zoegana adults.
Relative Effectiveness
It is anticipated that this moth will be an effective control agent in
conjunction with other root boring and seed feeding insects. Spotted and
diffuse knapweed patches are hard to find in Europe because they are kept
under control with the native insects and diseases.
Conservation
Sites that are chosen for A. zoegana releases should be considered
for long term availability. It is wise to consider at least a time commitment
of ten years without disturbance of the site by development or pesticide
use. For best establishment results A. zoegana should be released
in areas where there are green knapweed rosettes in August and in the
area of the knapweed patch where the knapweed is abundant but not a monoculture.
For general information about conservation of natural enemies, see Conservation
in the Tutorial section on this site, or the Volume II, No. 1 Feature
Article on conservation in the Midwest
Biological Control News Online.
References
Muller, H. (1989) Growth pattern of diploid and tetraploid spotted knapweed,
Centaurea maculosa Lam. (Compositae), and the effects of the root-mining
moth Agapeta zoegana (L.) (Lep.: Cochylidae). Weed Research, 29:103-111.
Muller, H., Schroeder, D., and Gassmann, A. (1988) (Agapeta zoegana
(L.) (Lepidoptera: Cochylidae), a suitable prospect for biological control
of spotted and diffuse knapweed, Centaurea maculosa Monnet De La
Marck (Compositae) and Centaurea diffusa Monnet De La Marck (Compositae)
in North America. Can. Entomol., 120: 109-124.
Story, J.M., Boggs, K.W., and Good, W.R. (1990) First report of the establishment
of Agapeta zoegana L. (Lepidoptera: Cochylidae) on spotted knapweed,
Centaurea maculosa La Marck, in the United States. Montana Agricultural
Experiment Station, Western Agricultural Research Center, Corvallis, MT
59828.
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