Biological Control Agent:  Longitarsus jacobaeae (Waterhouse)

Invasive Plant Species Attacked: Tansy ragwort (Senecio jacobaeae)

Type of agent: Root feeding flea beetle

Status

Description and Biology

Adult:

Males are 2.5 – 3. 5 mm long and females are 1 mm larger. Their colour changes from initially golden-tan to light golden-brown when mature; further changing to dark brown when old. They have enlarged rear legs that enable them to leap great distances.  Adults emerge in early spring to early summer (May – June), feed a short time and rest until late summer or early fall (September).  When they reappear later in the season they feed intensely.  The shortened days activate sexual changes in both males and females. In areas where continuous long days occur, 99% of beetles will not become reproductive.  Females stop dispersing once they become reproductive in the fall.  Oviposition is delayed until October when ideal habitat will offer 3.5 months of suitable weather.  Sites which are too cool will inhibit oviposition.  Mating and oviposition continues until freezing temperatures arrive.  Each female will lay between 500 and 1000 eggs, which are deposited individually at the root crown or leaf petiole base.

Egg:

Eggs are oval and measure 0.66 mm x 0.3 mm. Initially yellow, they darken during the 14 – 16 day incubation period.  Eggs are vulnerable to dry conditions, therefore, long moist autumns are necessary.

Larva and pupa:

White slender larvae hatch from eggs and begin to feed on the root crown.  Newly emerged larvae are 1.5 mm long, growing to 2 – 4 mm long over 8 – 14 weeks.  Development continues on the outer root layers, often penetrating into the root core.  Long grooved formations within the roots are the result of feeding on the outer layers.  In crowded or waterlogged conditions, they will feed on crowns and within the petioles of lower leaves.  Mature larvae will move to the soil to pupate, doing so up to 5 cm from the plant.

Overwintering stage:

Typically, larvae overwinter in plant roots. Eggs also overwinter in some populations.  In mild climates adults can hibernate during the winter months.

Location and effectiveness of attack

Adults create ragged shot-hole feeding causing little impact to the plant.  Larvae feeding on roots can kill small rosettes, but heavy attack is required to impact large plants.  A release of 1092 beetles onto a site in Nanaimo had 97% of plants attacked, with an average five larvae/root in eight years.

Predicted and native habitat

Longitarsus jacobaeae requires sunny locations with high density plants growing in well drained soils.  It does not tolerate flooding, heavy shade, or elevations over 400 m.  In the Pacific Northwest it has not established east of the Cascade Mountains.  Areas with long, moist autumns are required.

L. jacobaeae has a native distribution from Ireland to Siberia and Tibet. It is common to areas in central Italy, Sardinia, south Scandinavia, and from Ireland to east Georgia.  In Western Europe, it is limited to latitudes between 40 – 57 °N, further restricted in the Ukraine to south of 50 °N.

British Columbia Experiences

In 1971, L. jacobaeae were brought to BC via California and divided for lab rearing at UBC and into an open release in Abbotsford. Subsequent releases were made over several years throughout the lower mainland and on Vancouver Island.  It has been released into the Coastal Douglas-fir, Coastal western-hemlock and Interior Douglas-fir biogeoclimatic zones.  Establishment is restricted to the lower mainland and coastal environment, remaining unsuccessful in the south Okanagan.  Dispersal throughout the Coastal Region is wide spread.  Adults, larvae, and foliar feeding can be observed in these areas starting in August.

Collection for redistribution

Not available for general distribution at this time.

Notes

Combined efforts with Tyria jacobaeae offer excellent control as each agent has a preference for plant size, therefore attacking the multiple generations of tansy ragwort on a site.

A study of 42 sites in Oregon had 93% decrease in tansy ragwort plants in six years.

References

Harris, P. and S. Crozier. 2006. Classical biological control of weeds established biocontrol agent Longitarsus jacobaeae (Waterhouse) L. flavicornis Stephens and L. succineus Foudras. Ragwort root beetles.. Gov. of Can., Agriculture and Agri-Food Canada. February 9, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/alongflv_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.

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.