Left: Sphenoptera jugoslavica adult. V.Farquhar.
Right: Diffuse knapweed root damage caused by S. jugoslavica larva. R.Richard.

Sphenoptera jugoslavica
(Coleoptera: Burprestidae)

by Ronald Lang, USDA-APHIS-PPQ, Forestry Sciences Lab, Montana State University, Bozeman, MT 59717-0278.

Sphenoptera jugoslavica, a root boring beetle, was first released in the United States in 1979. 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.

S. jugoslavica has been released in Arizona, Colorado, Idaho, Montana, Nebraska, Nevada, Oregon, South Dakota, Utah, Washington, and Wyoming. It is established in Colorado, Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming, and is being collected for redistribution in Colorado, Montana, Oregon, and Washington.

Appearance

S. jugoslavica is a flat, metallic, copper colored, elongated beetle measuring 7 mm long. The larvae have an enlarged head and a long thin body. The larvae cause a gall-like swelling in the knapweed root near the crown.

Habitat

Diffuse knapweed infested areas.

Pests Attacked

European field collections found S. jugoslavica was limited, almost exclusively, to diffuse knapweed roots. The host-specificity tests indicated that the beetle could lay eggs and have them develop on diffuse knapweed, spotted knapweed, and yellowstar thistle.

Life Cycle

S. jugoslavica overwinters as larvae in the root of the knapweed plant. The newly formed adults remain motionless inside knapweed roots in their pupal chambers for two to five days. Then they bite a hole in the gall wall and leave the root. Adult S. jugoslavica emerge in July. The new adults feed on diffuse knapweed leaves for two to three days before mating. Egg laying commences in ten to twelve days after emergence. Adult S. jugoslavica live up to thirty days.

Pesticide Susceptibility

Not yet known.

Commercial Availability

Available commercially (see the off-site publication, Suppliers of Beneficial Organisms in North America).. In some states, S. jugoslavica adults may be obtained at no cost from state weed management agencies.

Effectiveness

Small knapweed rosettes that have been attacked often die by the end of the next season. Diffuse knapweed plants that survive are stunted and produce less flowers. After the beetle population has built up for five to six years, the knapweed population may collapse with only scattered knapweed plants remaining. This effect has been observed in drier areas where the beetles have been released. Stunted and unhealthy plants were observed in Europe especially in drier areas.

It is anticipated that this beetle will be an effective control agent in conjunction with other root boring and seed feeding insects. Diffuse knapweed patches are hard to find in Europe because they are kept under control by the native insects and diseases.

Conservation

Long-term availability is important in sites that are chosen for S. jugoslavia releases. It is wise to consider sites that will be undisturbed by development or pesticide use for at least ten years. Releases should be made in sections of the diffuse knapweed infestation where the plants are at least one to two feet apart with some bare ground showing. The beetle seems to thrive in drier areas and on diffuse knapweed.

For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, or the Volume II, No. 1Feature Article on conservation in the Midwest Biological Control News Online.

References

Powell, R. D. (1984) Some preliminary results concerning the beetle Sphenoptera jugoslavica as a biological control for diffuse knapweed. Proceedings of the Knapweed Symposium, Cooperative Extension Service, Montana State University, Bull. 1315: 45-51.

Powell, R. & P. Harris (1986) Biological control of diffuse knapweed by Sphenoptera jugoslavica (Obenb.). Agriculture Canada, Ottawa, Canada. Canadex: Insects - Diseases - Pests, Weed Control: Beneficial Insects 641.613.

Powell, R. D. and Myers, J.H. (1988) The effect of Sphenoptera jugoslavica Obenb. (Col., Burprestidae) on its host plant Centaurea diffusa Lam. (Compositae). J. Appl. Ent. 106: 25-45.

Zwolfer, H. (1976) Investigations on Sphenoptera (Chilostetha) jugoslavica Obenb. (Col., Buprestidae), a possible biocontrol agent of the weed Centaurea diffusa Lam. (Compositae) in Canada. Z. ang. Ent. 80:170-190.

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