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

A. plagiata was brought to BC in 1967.  Two field treatments were made in the west Kootenays and establishment was later confirmed.  Two adult specimens collected in May (2005), laid 35 eggs and all hatched one week later.  The larvae survived for 15 days in captivity, and were then transferred to a field site.  In the lower Southern Interior, adults are common in May and several stages of larvae can be seen in early to mid August.

Collection for redistribution

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 perforatuna 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.