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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, Feature Article on conservation in Volume II, No. 1 of Midwest Biological Control News.

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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