Hosts or Prey
Hypericum plant species including Klamathweed, or St. Johnswort. Depending on the situation, Hypericum-feeding beetles are beneficial as discussed here or are pests.
Identification
The adult, a leaf beetle (family Chrysomelidae), is oblong and about 1/4 inch (6 mm) long with a downward-pointed head. It is metallic shiny and dark blue, bronze, green, or purple. Eggs are oblong and about 1/25 inch (1 mm) long.
Larvae are plump and somewhat humpbacked. They are gray, orangish, or pinkish and grow up to 1/4 inch (6 mm) long. The oblong pupae occur hidden in individual cells in topsoil.
If Hypericum species have ragged-edged, chewed leaves, shoots, and stems the likely cause is feeding by adults or larvae of a Chrysolina species, in California most commonly C. quadrigemina. Larvae feed on lower leaves and the base of stems during fall through winter. Adults feed higher up on plants. Their chewing damage occurs primarily during spring and early summer when hosts produce most of their growth flush and flowering. Adults feed to a lesser extent again during the fall.
Life Cycle
Klamathweed beetle develops through 4 life stages: egg, larva, pupa, and adult. Eggs are laid from fall through winter singly or in clusters on leaves. Each adult female can lay about 1,000 eggs during her life span of several months.
After hatching, larvae feed during late fall through winter and develop through 3, increasingly larger instars. Mature larvae (prepupae) enter soil to a depth of about 1 inch during late winter and form a cell in which they pupate. Adults emerge primarily in April and May, mate, and mostly feed during spring and early summer.
During hot, dry summer weather adults aestivate (are inactive and do not feed). Adults again become active in fall, feeding and laying eggs. The beetle overwinters primarily as eggs or larvae. Klamathweed beetle has one generation per year.
Habitat
Klamathweed is an exotic, invasive plant native to Europe that was inadvertently introduced into the United States. By the early 1940s, Klamathweed had spread to cover over 2 million acres of rangeland and wildlands in California. In addition to crowding out native vegetation on which various wildlife species depend, Klamathweed is toxic when fed upon by cattle and sheep.
To address these problems, entomologists from the U.S. Department of Agriculture and University of California obtained from Australia several insects that had been imported from Europe to control Klamathweed in Australia. Studies under quarantine revealed the insects do not feed on beneficial plants. Therefore, beginning in 1946 these natural enemies of the weed were introduced in California. Chrysolina hyperici and C. quadrigemina became well established and spread throughout the state wherever Klamathweed occurs. By 1957, Klamathweed abundance was reduced by over 99% and the weed was eliminated from many areas. Each year into perpetuity this classical biological control program saves ranchers millions of dollars in otherwise lost grazing land and poisoned livestock.
Subsequent to the beetles' introduction, other Hypericum plant species became popular ground covers and shrubs in California landscapes. These, especially creeping St. Johnswort, H. calycinum, are also fed upon by the Chrysolina leaf beetles. However, Hypericum in irrigated landscapes generally tolerates the beetle feeding and the chewing damage is primarily aesthetic. Where Klamathweed beetle is a pest of desired Hypericum, for management see Klamathweed Beetle—Chrysolina quadrigemina.
Species
Over 400 species of leaf beetles occur in California. These include at least 7 Chrysolina species: C. bankii, C. extorris, C. flavomarginata, C. hyperici, C. quadrigemina, C. schaefferi, and C. varians.
More Information
- Biological Control of Klamathweed—Progress Report, U.S. Department of Agriculture
- Chrysolina quadrigemina (Coleoptera: Chrysomelidae) Klamathweed Beetle, Cornell University
- The Role of Chrysolina gemellata [=C. quadrigemina] in the Biological Control of Klamath Weed, U.S. Department of Agriculture and University of California
- St. Johnswort, Biological Control in the Western United States, UC Agriculture and Natural Resources
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Chrysomelidae
