BIOLOGICAL CONTROL OF KLAMATH WEED - PROGRESS REPORT
1/ James K, Holloway, U.S.D,A»j Agricultural Research Administration, U, S. Bureau of Entomology and Plant Quarantine,
(Prepared for Delivery at Western Weed Control Conference, Sacramento, California, February 2, 1948)
Chemical control of Hypericum perforatum, called Klamath Weed in
California, has had a long and interesting history. In most places the
cost of materials and the inaccessibility of the land to be treated have
been limiting factors. Recently the application of borax has been used to control new and small infestations. The use of borax for this purpose
is highly recommended by the various agencies engaged in weed control programs.
Biological control of the Klamath weed by insects has been under
consideration for several years as a desirable approach to the
problem. In 1920 the Commonwealth of Australia began a search for
insect enemies of Hypericum in England, according to a report by Currie and Garthside (1932). Early in 1935j after the introduced British
species apparently had failed to become established in Australia, the work was transferred to southern France, the results of which were published by Wilson (1943)• The preliminary work in Europe consisted of tests to determine whether a considerable number of insect species
fed or reproduced on representative plants of economic importance - that is on 42 widely distributed species belonging to 19 families.
After the satisfactory conclusion of the tests in Europe, the
species that had neither fed nor reproduced upon the test plants were
1/ Also an Associate in the California Agricultural Experiment Station, Division of Biological Control, Carl B. Huffaker, of the University of California, has been working on the project since January 1946, exported to Australia. Before liberations oould be made there, how¬ ever, it was necessary to make additional tests on plants that did not grow in Europe. The progress of the Australian experiment was followed in California with much interest. About 8 years after releases in
Australia, of two species of Ghrysolina known as hyperici (Forst.) and gemellata Rossi, encouraging results were reported by A. J. Nicholson, in correspondence with Harry S, Smith, of the University of California,
College of Agriculture, Negotiations between the University of California and the Bureau of Entomology and Plant Quarantine, United States
Department of Agriculture, regarding the advisability of introducing the beetles into California resulted in an authorization by the
Department of import Ghrysolina hyperici, C. gemellata and Agrious hyperici Creutzer, with the proviso that feeding tests be made on the following plants: Sugar beet, flax, hemp, sweet potato, tobacco, and cotton* A cooperative project for the importation^ testing, and colonization of these species was then set up between the two organiza¬ tions. The Second World War matde it impossible to make collections in Europe. An abundance of material was available in Australia, how¬ ever, and it could be transported to California by the U. S. Army Air
Transport Command. The Australia Council for Scientific and Industrial
Research, through Dr. Nicholson, offered to collect and ship the needed material. The collection and preparation of the insects for shipment was under the immediate supervision of T. G, Campbell, research officer of this Council,
Importations were begun in October 1944. The first problem was to change the life cycles so that they would be in phase with the seasons of the Northern Hemisphere, Specimens of Agrilus hyperici
-2- were received as mature larvae in roots. Some of the larvae were
retarded in cold storage, but others were forced to emerge upon
arrival. Neither method gave satisfactory emergence of adults, further
importations were curtailed until the Bureau laboratory in Europe could
be reopened. Material was subsequently received during 1947. Starv¬
ation tests have been completed, but no liberations are to be made
until after the distribution and effectiveness of the two leaf-feeding
species has been studied.
The two species of Chrysolina were occasionally shipped as mature
larvae that would emerge as adults upon arrival, feed, and enter aestiva¬
tion about 3 weeks later. Most of the shipments, however, consisted of
aestivating adults. In either case the problem was to bring the adults out
of aestivation into the egglaying phase. By subjecting the adults to fine
sprays of water each day, fertile eggs were obtained mthin 2 to 3 weeks.
In 1944 sufficient specimens of Chrysolina hr/perici were received
for conducting the feeding tests. The tests were completed in May
1945, no feeding or egg laying having taken place on any of the test plants, and four colonies v/ere released late in the season. One
colony became established, but the survivors were so few that it was impossible to make recoveries until 1947,
Approximately 370,000 adults of Chrysolina hyperici were liberated
from 1945 through 1947. Of this number, 3,500 were reared in the
insectary. Insectary rearing presents a difficult problem, because there are several generations of coimon greenhouse pests to one of
C. hyperici. Small-scale rearing can be handled by transferring larvae to fumigated Hypericum plants once or twice during the four instars of of larval feeding, but such a procedure is costly and is not suited to an extensive program.
-3- Liberations of Chrysolina hyperici prior to 1947 had been made in nine different colony sites distributed amoung five counties in California.
Seven of the nine colonies have become established, and already in two locations complete destruction of Klamath weed can be seen within a radius of 15 yards around the original release locations.
During 1947 releases were made in 12 additional counties in
California making a total of 66 new colonies and 2 experimental colonies were started in Oregon. It is hoped that these releases will furnish each county with colonies which can later be used as a source of material for local distribution.
The feeding tests with Chrysolina gemellata were completed on
January 26, 1946. A total of 13,650 adults of this species were released in one location in each of four counties. The releases were made in
February 1946 from imported material that had been received during the preceding two months. All the colonies became established and large increases were noted during the first partial generation. During the second season, 1946-47, two of the colonies did exceptionally well. At the time of their emergence in April and May 1947 the adults could be found readily a quarter of a mile from the point of release.
During the winter of this second season the destruction of the basal growth of Klamath weed by the larvae was very apparent, and the results of this feeding were evident on new upright spring growth. In the areas of little larval feeding each plant had four or five up- rights, whereas in the heavily infested areas the upright gro-wt-h ranged from none to two small stems. The emerging adults stripped the remaining one or two stems of all their leaves, and an area several yards in diameter is now devoid of any living weed. At the present
-4- the egg and larval populations are far in excess of those of the previous
year.
The importations received during 1947 contained an estimated 5 per
cent of Chrysolina gemellata. Releases were made in units of 5^000 beetles;
thereforeJ each colony site of C, hyperici received approximately 250
C. gemellata. Past experience- with this species indicates that this
small number would be sufficient to start a colony should hyperici
fail to become established in any location.
Briefly, the life history of the two species of Chrysolina is as
follows: In the spring as the flower buds are forming the adults emerge
They feed voraciously on the leaves and tender stems of the plants. A
month or so later the plants become dry and unsuitable as food, and the
adults cease feeding and enter a period of aestivation which lasts
throughout the summer months. With the first fall rains procumbent
basal growth commences. At this time the adults come out of aestivation
and feed sparingly on the new foliage. After a week or two they mate
and begin to lay eggs. The egg laying continues throughout the winter
months. The rate of deposition and the duration of the egg and larval
stages are dependent upon the temperature. All the larvae, regardless
of hatching time, reach maturity in the springy and pupation takes *
place at about the time the erect stems of Klamath weed are half grown.
Adults of the new generation emerge as the buds are being formed, one
life cycle being completed in a single year.
Some of the progency of now successful colonies will be used for
liberation in more northern out-of-State locations as soon as collections
can be made without depleting the mother colonies. It may be possible to start on a small scale this year. Material collected and liberated in the late spring at about the time the beetles enter aestivation become synchronized with the plant growth more readily, as conditions which promote the basal grovjth in the fall also bring the beetles out of aestrivation. As previously stated, it is possible to bring the imported adults out of aestrivation the first year and have them in step with the seasons of the Northern Hemisphere, Under the best conditions, however, this cannot be accomplished until January, which means that the beetles are two or three months behind their normal egg laying schedule. Therefore, the new colonies originating from importations do not increase so rapidly at those that are made up of beetles from colonies already in synchronization.
As soon as the distribution phase is completed, the problem will then enter upon the control phase. At present it is difficult to formulate any exact ideas as to the outcome, but control is reported to be effective in Australia, and the two important species Chrysolina hyperici and gerne11ata, have become established here. The progress of the work has been satisfactory, and the outlook for the future is good. However, it should be remembered that a biological control pro¬ gram of this kind requires a considerable time before large-scale reductions can be had. Therefore, at present, there should be no relaxation of the control programs which are being followed.
Literature Cited.
Currie, G, A., and S. Garthside 1932, The possibility of the entomological control of St. John's Wort in Australia- Progress Report, Austral Council Science and Industry Research Pam. 29, 2Spp,
Wilson, Frank, 1943. The entomological control of St, John's Wort (Hypericum perforatum L,) with particular reference to the insect enemies of the weed in southern France, Austral, Council Science and Industry Research, Bui. l69, 37 pp.
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