Changes in Range Plant Population Structure Associated with Feeding of Imported Enemies of Klamath Weed (Hypericum Perforatum L.)

Huffaker, C.; Holloway, J.

Changes in range plant population structure associated with activities o introduced natural enemies (Chrysomela gemallata and C. hyperici) of Klamath weed (Hypericum perforatum), an aggressive perennial weed which has taken over vast open range areas and has a moderately toxic property, were studied over a period of 3 seasons subsequent to the release of these beetles in California. A brief review of some of the pertinent literature reveals that the dominant vegetative cover in certain areas of Australia, Hawaii, New Zealand, Fiji, and Africa, for example, has on occasion been greatly changed through the action of insects. Most of these insects has been purposely introduced in an effort to achieve biological control of weedy, alien species which had taken over huge tracts ofland. Among these examples are prickly-pear control through the introduction of Cactoblastic cactorum into Australia; lantana by several introduced insects in Hawaii; Clidemia by Liothrips urichi in Fiji; Acaena spp. by a sawfly, and gorse by the weevil (Alpion ulicis) in New Zealand. Studies were made in three areas in California, one indicative of the Sierra foothill region, and twoof the Northern Coast Range. Data from quadrats at the release centers and at various fixed distances, up to 600 yards from the centers, reveal that feeding by larvae of the two introduced beetles had taken out the dominant Klamath weed at all positions where the beetles had attained a dense population, whereas the weed maintined its earlier vigor or increased in the check areas studied. Only 5.000 C.gemellata and 1,300 C. hyperici had been released at Blocksburg and Fort Seward, resp[ectively, in Humbold

Changes in Range Plant Population Structure Associated with Feeding of Imported Enemies of Klamath Weed (Hypericum Perforatum L.)

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