Chrysolina varians (Schaller)
Attacks: St. John's Wort
Agent Type: Foliar feeding beetle
Origin: C. varians released in BC orginated in Sweden.
Adult: C. hyperici & C. quadrigemina beetles The beetles are metallic bronze, brown or greenish coloured. Adults emerge in early-June and begin feeding in clusters on young terminal leaves, flower buds or the underside of leaves. They continue to feed until leaf drop in July and early-August. Reproduction is related to day length; with longer daylight, less feeding and reproduction occurs. When day length is reduced they move into plant litter and await the fall rains. Once precipitation breaks dormancy, mating and egg laying begins. Females oviposit eggs individually or in small clusters on winter basal leaves.
Egg: The elongated, 1.2mm x 0.5mm orange eggs overwinter and hatch the following spring. The eggs incubate for 6-7 days.
Larva/Pupa: Chrysolina varians larvae The plump, humped-back larvae, initially orange coloured, change to dirty pink-grey as they mature. The eggs that have overwintered usually hatch in May. The new larvae feed on buds and immature leaves causing complete defoliation before moving on to adjacent plants. Feeding on St. John's wort causes the larvae to become light sensitive. Photosensitivity prevents them from feeding during the day, and they must feed during low light periods before sunrise. After the morning feed they seek shade and protection, the smallest hide in leaf buds while the larger ones move under the plants or into the soil. They resume feeding at sunset. Mature larvae burrow into the soil during spring and early summer and create a pupal cell.
Overwintering: Overwinters in egg form on fall/winter basal leaves.
Location & Efficacy: Early spring larvae feeding on fleshy new growth cause the most damage. Although adult feeding can be impressive, it has less impact than early larvae feeding. Heavy fall feeding may cause some impact on the plants' ability to overwinter.
Habitat: Chrysolina varians habitat appears narrower than other Chrysolina species. It may be best suited for maritime climates since it does not tolerate hot dry conditions. It requires soft soils for pupation, avoiding rocky or barren sites. As with other Chrysolina it requires open sunny locations, avoiding shaded and forested areas.
Its native distribution is from Spain to west Siberia. C. varians occurs in northern and alpine areas of Europe and is common where summers are moist. In harsh winter habitat it requires sufficient snow cover for protection. In Sweden it is found abundantly in moist forest openings and at sites with low canopy bushes. In BC, C. varians was released into the Bunchgrass and Interior Douglas-fir BEC zones. Early monitoring determined it did not establish and it was thought the sites may be too dry. Bunchgrass and Ponderosa pines biogeoclimatic zones are probably not favourable for this particular species.
BC History: C. varians was one of three Chrysolina species introduced to BC. A pure population was released 1957 near Westbank into a buchgrass habitat surrounded by Ponderosa pine. No evidence of the beetle was found the following year and it was presumed the site was too dry to support this Chrysolina species. The area has undergone significant development since the release. In 1958 another release was made into an area dominated by Interior Douglas-fir and short term establishment was found.
Field Results: Historical records indicate that the second C. varians release only survived one winter. A few beetles were found one year later, but no further evidence was found in subsequent years. If it did establish long term, it may now be found only in mixed populations with the two other Chrysolina species.
Handling/ Collecting: By early-June, adults can be swept when they cluster on the plants.
Notes: C. varians is similar to the other Chrysolina species released in BC making identification difficult in the absence of the other species for comparison.