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Biological Control : A Guide to Natural Enemies in North America Anthony Shelton, Ph.D., Professor of Entomology, Cornell University

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Chrysolina quadrigemina
(Coleoptera: Chrysomelidae)
Klamathweed Beetle

The importation in 1944 of Chrysolina quadrigemina and its close relative, C. hyperici, was the first North American attempt at controlling weeds with insects. The insects are natural enemies of Hypericum perforatum, known as Klamath weed in the Western U.S., goat weed in the Mountain States, and, more generally, as St. John's wort. This native European plant is a pest on rangelands throughout the temperate regions of the world because it displaces forage plants and is toxic to cattle and sheep. In 1943 it was estimated that 400,000 acres of California rangeland were infested with Klamath weed.

The native range of C. quadrigemina is from North Africa to Denmark, not extending as far north as Sweden. In 1944, an introduction program into North America was initiated, but it was not possible to obtain European insects because of the war, and so specimens were imported from Australia, where they had previously been established. This required changing the life cycles of these Southern Hemisphere insects to be in phase with the Northern Hemisphere. Fine, daily sprays of water were administered, which caused the adults to emerge from aestivation, a heat or drought induced quiescent period, and to lay eggs. Finally, the small imported population increased enough to complete feeding tests, and the beetles were released in February of 1946.


C. quadrigemina is up to 1/4" in diameter. Although not brightly metallic, it has a metallic sheen that can be green, bronze, purple, and/or blue, depending on the individual.


Rangeland infested with Hypericum perforatum.

Pests attacked

C. quadrigemina is generally specific to H. perforatum. It has been reported feeding on some native and ornamental Hypericum species, but it does not prosper. It is not known if it can complete its life cycle on species other than H. perforatum.

The Klamathweed beetle is very closely synchronized in its growth stages with the host plant. In 1943, negotiations between Harry S. Smith, Chairman of the Department of Biological Control at the of the University of California and the USDA Bureau of Entomology and Plant Quarantine, resulted in an agreement that C. quadrigemina and two other potential Klamath weed control agents would be tested, prior to release, on 6 plants to which the insects had not been exposed in Europe or Australia: sugar beet, flax, hemp, sweet potato, tobacco, and cotton. Upon satisfactory completion of the tests, the Klamathweed beetle was released.

Life cycle

Adults emerge from pupal cells that are just beneath the soil surface in April and early May when the plants are producing flower buds or are actually in flower. They feed voraciously on the plant foliage until late June/early July, and then, fully fed, spend an obligate period of aestivation beneath stones and debris and in crevices of the soil. The aestivation period cannot be entered in moist conditions. With the onset of fall rains, the beetles again become active, in synchrony with the host plants. The plants form a leafy, basal growth upon which active beetles feed sparingly, then mate and lay their eggs about mid-October. The larvae reach the third- and fourth-stages of development by feeding on the plant's basal growth, which they completely destroy. They then enter the soil to a depth of about one inch and individually form cells for pupation. There is one generation per year.

Relative effectiveness

Because its life cycle is so well synchronized with Klamath weed growth habits, C. quadrigemina is very effective against this plant pest if it is located in climates suitable for the beetle.

After the initial North American release in 1946, C. quadrigemina multiplied so quickly that at one location two years later, 5000 beetles, a small fraction of the total population, were collected for redistribution. By 1951, populations were established in all 21 California counties in which Klamath weed was a problem, and the plant was already under control in some of the original locations. By 1957, the plant was reduced by 99% in Northern California.

C. quadrigemina is adapted to a climate with hot, dry summers and mild, rainy winters, and all stages of C. quadrigemina – eggs, larvae, pupae, and adults – are able to withstand winter temperatures of California areas that support Klamath weed. Adults and larvae are susceptible to frosts, but all stages can survive under snow cover.

Canadian efforts have had mixed success. In 1951, releases in British Columbia of C. quadrigemina and C. hyperici (a species more tolerant of moisture) have resulted in effective control of St. Johns wort in many areas of the province. Both of these species have been introduced and become established in southern Ontario. More recently, C. quadrigemina has been reported in New York, Pennsylvania, Ohio, Maryland, and West Virginia, and is presumed to have spread from release sites in Ontario.

In areas where the Klamathweed beetle thrives, St. Johns wort is reduced to an acceptable level or is at least subjected to extensive damage. However, in moist areas, C. quadrigemina introductions have done little to control the weed, even when the beetle persists. Cold is another negative factor, and in one year of heavy frost, the C. quadrigemina population at a Canadian site (Zamora-Westbridge vicinity) collapsed. The presence of trees and dense ground vegetation helps to protect the beetles from frosts.


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.

Commercial availability

Available commercially. See the off-site publication, Suppliers of Beneficial Organisms in North America.


Thanks to Noah Poritz of Biological Control of Weeds, Inc., for supplying photographs and information.


Environment Canada. 1997. Invasive Plants of Natural Habitats in Canada: An Integrated Review of Wetland and Upland Species and Legislation Governing their Control. Upland Species Accounts.

Hare, J. D. 1997 Course Outline: "Insect Ecology," Biology/Entomology 127, University of California, Riverside.

Harris, P., Peschken, D., and Milroy, J. 1969. The status of biological control of the weed Hypericum perforatum in British Columbia. Can. Entomologist, 101: 1-15.

Holloway, J. K., and Huffaker, C. B. 1951. The role of Chrysolina quadrigemina in the biological control of Klamath weed. J. Econ. Ent. 44: 244-7.

Hoebeke, E.R. 1993. Establishment of Urophora quadrifasciata (Diptera: Tephritidae) and Chrysolina quadrigemina (Coleoptera: Chrysomelidae) in Portions of Eastern United States, Ent. News, 104: 143-152.

Holloway, J. K. 1957. Weed control by insect. Ecology, Evolution, and Population Biology, Readings from Scientific American. W.H. Freeman and Co., San Francisco. 319 pp.

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Top: C. quadrigemina adult. Photo: Courtesy of USDA/ARS

Bottom: Adult Chrysolina. Note the metallic sheen. Photo: Courtesy of Noah Poritz, Biological Control of Weeds, Inc.

Top: C. quadrigemina adult.
Photo: Courtesy of USDA/ARS

Bottom: Adult Chrysolina. Note the metallic sheen.
Photo: Courtesy of Noah Poritz, Biological Control of Weeds, Inc.

Top: Chrysolina quadrigemina beetles on St. John's wort. Photo: Courtesy of Noah Poritz, Biological Control of Weeds, Inc.

 Bottom: C. quadregemina adults  clustered on tops of St. John's wort. Photo: Courtesy of USDA/ARS

Top: Chrysolina quadrigemina beetles on St. John's wort.
Photo: Courtesy of Noah Poritz, Biological Control of Weeds, Inc.

Bottom: C. quadregemina adults
clustered on tops of St. John's wort.
Photo: Courtesy of USDA/ARS

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