Biological Control Agent: Chrysolina hyperici (Forst.)
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-green coloured and measure 5.3 - 6.1 mm long. The
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. This changes when day length is reduced. At this time they move into plant
litter and await the fall rains. A significant amount of moisture is needed to break
dormancy. If dormancy is not broken, mating and egg laying is delayed until the following
spring, which is often the case in Canadian habitat. Adults that do reappear in the autumn
will mate. Females oviposit up to 2000 eggs individually or in small clusters onto basal
winter foliage. Chyrsolina hyperici adults are hardier, smaller, and appear later
in the spring than C. quadrigemina. Colouring can vary between sites, more bronze
coloured adults are found in mild climates.
Egg:
The elongated 1.2 mm x 0.5 mm orange eggs overwinter and hatch the following spring.
The eggs are susceptible to desiccation.
Larva and pupa:
The plump, humped-back larvae, initially orange coloured, change to dirty pink-grey as
they mature. Newly hatched larvae usually appear in the spring, although some will hatch
in the fall. They feed on leaf 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 late spring and early summer and create a pupal cell.
Overwintering stage:
In most cases it overwinters as an egg. However, adults and larvae can also overwinter;
both have good winter survival in mild climates or under snow cover.
Location and effectiveness of attack
Early spring larvae feedings on fleshy new growth cause the most damage. This timing
is the controlling key. Although adult feeding can be impressive, it has less impact
than larvae feeding. Heavy fall feeding may cause some impact on the plants ability to
overwinter.
Predicted and native habitat
C. hyperici adapts well to ocean or maritime climates, accepting moister sites than C.
quadrigemina and tolerates higher summer precipitation than other species. It
can withstand cold climates with little or no snow cover. It requires soft soils, sites which
are rocky or barren are undesirable. It needs open sunny locations; avoiding shaded and
forested areas. It is adaptable to environmental conditions, enabling it to persist when
other species fail.
C. hyperici is native in the Atlantic regions of Europe. In Scandinavia it
is restricted to the coastal areas. In Rumania it has shown a higher tolerance for dry
conditions than C. varians.
British Columbia Experiences
Origin:
C. hyperici released in BC came from reared populations from Loftus,
California. The California stock arrived from Australia that originated
from populations from Great Britain.
History:
C. hyperici was one of the two species introduced to BC near Fruitvale in 1951.
Imported populations for field release continued for several years. These early established releases
provided collection sources for future BC populations and the first field
collection occurred in 1981. Over the next few years Chrysolina species were released in several
locations in the southern interior. Subsequent releases have established and the
beetles have dispersed freely with limited assistance.
Habitat:
Releases have been made into the Coastal western hemlock, Interior
Douglas-fir and Ponderosa pine biogeoclimatic zones. Establishment was
found at the Interior Douglas-fir zone site and is suspected to be established
in the other zones in a mixed population. Dispersal of Chrysolina
species is found in Coastal Douglas-fir, Coastal western hemlock,
Engelmann spruce-subalpine fir, Interior Douglas-fir, Montane spruce and
Ponderosa pine zones. Some southern interior habitats include elevations
to 1100 m. On dry Ponderosa pine sites, C. hyperici replaces C. quadrigemina.
Field results:
In recent years St.
John's wort has been re-establishing and, therefore, renewed efforts have been
underway to assist with redistributing the beetles in mixed populations.
In the southern interior, larvae are readily seen in May and adults are abundant in June.
By early June, adults can be swept when they cluster on the plants.
Notes
C. hyperici are similar to other Chrysolina species released in BC making identification
difficult in the absence of the other species for comparison. C. hyperici adults
are smaller than C. quadrigemina and emerges later in the fall. They also
more frequently delay oviposition until spring, therefore, laying fewer eggs in the fall.
Of the two, C. hyperici is hardier.
Summer rains do not affect its dormancy.
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. 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.
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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