Biological Control Agent: Chrysolina varians (Schaller)
Invasive Plant Species Attacked: St. John's wort
(Hypericum perforatum)
Type of agent: Foliar feeding beetle
Status
Tertiary
Description and biology
Adult:
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 (May to September in Europe). 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. This changes when day length is reduced. At this time
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, 1.2 mm x 0.5 mm orange eggs overwinter and hatch the following spring.
The eggs incubate for 6 - 7 days.
Larva and pupa:
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, therefore, they must feed during
low light periods, and do so 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 stage:
Overwinters in egg form on fall/winter basal leaves.
Location and effectiveness of attack
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.
Predicted and native habitat
Chrysolina varians habitat appears narrower than other Chrysolina species.
It may be best suited for maritime climates. It does not tolerate hot dry conditions.
It requires soft soils for pupation; avoiding sites which are rocky or barren. 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. It 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.
British Columbia Experiences
Origin:
C. varians stock originated from Sweden.
History:
C. varians was one of the 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.
Habitat:
C. varians was released into the Bunchgrass and Interior Douglas-fir biogeoclimatic zones.
Early monitoring determined it did not establish and it was indicated that the
sites may be too dry. Bunchgrass and Ponderosa pines biogeoclimatic zones are probably not favourable
for this particular species.
Field results:
Historical records indicate that the second C. varians release in
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 other the two
other Chrysolina species.
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.
References
Harris, P. 2003. Classical biological control of weeds established biocontrol
agent Chrysolina hyperici (Forst.). Defoliating beetle. Gov. of Can., Agriculture
and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/achryhyp_e.htm
Harris, P. 2003. Classical biological control of weeds established biocontrol
agent Chrysolina quadrigemina (Suffr.). Defoliating beetle. Gov. of Can.,
Agriculture and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/achryqua_e.htm
Harris, P. and D. P. Peschken. 1971. 32. Hypericum perforatum L., St.
John's wort (Hypericaceae). Biological Control Programmes Against Insects and Weeds in
Canada 1959-1968. Commonwealth Agricultural Bureaux. Pp. 90.
Kelleher, J. S. and M. A. Hulme, (editors). 1984. Biological control programmes
against insects and weeds in Canada 1969-1980. Commonwealth Agricultural Bureaux.
Manitoba Agriculture. No date. St. John's wort (Hypericum perforatum L.).
Brochure. Gov. of Man.
MFR field observations and comments.
Powell, G. W., A. Sturko, B. Wikeem and P. Harris. 1994. Field guide to the
biological control of weeds in British Columbia. B.C. Min. For. Res. Prog.
Rees, N. E., Quimbly, Jr., P. C., G. L. Piper, E. M. Coombs, C. E. Turner, N. R. Spencer,
L. V. Knutson (editors). 1996. Biological control of weeds in the west.
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