Biological Control Agent: Aplocera plagiata L.
Invasive Plant Species Attacked: St. John's
wort (Hypericum perforatum)
Type of agent: Foliar feeding moth
Status
Primary
Description and Biology
Adult:
The moths are overall light grey coloured and referred to as 'treble-bar moths'.
Their wingspan is between 2.7 and 4.0 cm. When at rest, the wings are held in a triangular
shape. The first generation adults emerge in May and June and do so in fewer numbers
than the summer generation. The second generation adults appear when the host plants
are flowering, usually from August to September. Mating and oviposition begins shortly
after the adults emerge. Females lay up to 300 eggs onto upper and lower leaf surfaces
or on stems. Adults make frequent erratic flight patterns when disturbed and land a short
distance away before taking flight again. They are strong fliers which enable them to
easily seek scattered patches.
Egg:
The eggs are oval-shaped and pearl white. They will incubate for 5 - 7 days.
Larva and pupa:
The 'inch worm-like' larvae develop through various stages and change from their initial
light brown/tan and green colour to darker brown with deep shading along their upper back and
with dark stripes along their body. When they are fully mature, the larvae will measure
2.2 cm long. When disturbed they will mimic dead twigs. The first generation appear
in early August. Newly emerged larvae feed on the plant leaves, avoiding toxic leaf glands
until they are old enough to have developed their immunity. Mature larvae burrow into
the soil to pupate which takes 12 - 17 days to complete. Pupae are slender and light
greenish-golden brown. The larvae can withstand high and low temperatures, but harsh
winters, high elevations, and northern locations may effect the overwintering generation if
they do not develop sufficiently before winter. Moist soils can cause fungal infections.
Overwintering stage:
Immature larvae overwinter in the soil and resume feeding the following spring.
Location and effectiveness of attack
The spring generation feeds on leaves and is capable of substantially defoliating plants.
The summer generation feeds on flowers. Foliar feeding is usually observed before the
larvae are located.
Predicted and native habitat
Aplocera plagiata is commonly associated with well drained soils in warm continental
climate areas. Dry sites with rocky or sand-based soils and some limestone are suitable. Wet
climates or moist soils are unsuitable.
In Europe, A. plagiata exists to the northern limits of St. John's wort, but does
not occur in warm dry sites.
British Columbia Experiences
Origin:
The A. plagiata populations released in BC originate from France, Germany and Switzerland.
History:
A. plagiata was brought to BC in 1967. Two field treatments were made in the
west Kootenays and establishment was later confirmed. Releases
continued from 1967 to 1987. The first BC field collection was
made in 1992 from a release site near Grand Forks. No further field
collections occurred until 2008.
Habitat:
A. plagiata releases have been made and found established in the
Coastal western hemlock, Interior cedar hemlock and Interior Douglas-fir
biogeoclimatic zones. Establishment has not been confirmed in Sub-boreal spruce near Quesnel. It is too soon to determine the
status of the recent attempt to move populations from the BC southern interior to Vancouver Island.
Field results:
Dispersal sampling done in 2008 indicate that the moth
is freely distributing itself throughout the southern interior.
Larvae have can easily be located during rainy periods, which indicates they may
tolerate for wet conditions. Two adult specimens collected
in May (2005), laid 35 eggs and all hatched one week later. The larvae fed
for 15 days in captivity, and were then transferred to a field site.
Not available for general distribution at this time.
Notes
This is the only inch worm found on St. John's wort.
This species was formerly known as Anaitis plagiata.
References
Harris, P. 2003. Classical biological control of weeds established biocontrol agent Aplocera
plagiata (L.). Gov. of Can., Agriculture and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/aaploplg_e.htm
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 perforata L.). Govt. of
Man., Sustain Ability Man., Piney/Stuartburn Weed Control District. (pamphlet) 6 p.
MFR staff 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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