Biological Control Agent:  Longitarsus flavicornis Steph.

Invasive Plant Species Attacked: Tansy ragwort (Senecio jacobaeae). 

Type of agent: Root feeding flea beetle

Status

Primary

Description and Biology

Adult:

Adults are reddish brown, but darken as they age. They are 2.5 – 3. 5 mm long and have enlarged rear legs that enable them to leap great distances.  Adults emerge in 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 weather conditions are suitable, which usually begins in October and continues until January.  Sites which are too cool inhibit oviposition.  Each female will lay between 500 and 1000 eggs.  Eggs are deposited up to 4 mm deep near plant roots with a small percentage laid on petioles.

Egg:

Eggs are oval and measure 0.66 mm x 0.3 mm. Surface laid eggs experience partial dehydration, but overall are less vulnerable to dry conditions than those of Longitarsus jacobaeae. Initially yellow, they darken during the 14-16 day incubation period. At 8 °C, eggs hatch in 88 days or in 14 days at 25 °C.

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. L. flavicornis does more external root feeding than L. jacobaeae, often consuming the entire outer layer and root cortex. The feeding cause the plants to have poorly developed, deeply mined and scarred roots. On the root crown they feed into the cortex, seldom feeding into the core. In crowded or flooded conditions, they will feed on crowns and within the petioles of lower leaves. Overwintering (November through May) larvae distribute to petioles, root crown, roots and in the soil. Mature larvae move to the soil to pupate, seldom remaining near the plants. By March, most larvae are in the third instar.

Overwintering stage:

Normally they will overwinter as larvae in the soil, however, in Canada they are expected to also overwinter as eggs.

Location and effectiveness of attack

Adults create ragged shot-hole feeding. Larvae feeding on roots can kill small rosettes, heavy attack is required to impact large plants. L. flavicornis feeds more aggressively on external root layers than L. jacobaeae. It often consumes all the outer epidermis and cortex, leaving only the central core intact.

Predicted and native habitat

L. flavicornis requires sunny locations with high density plants growing in well drained soils. It does not tolerate flooding, heavy shade or elevations over 400 m. Areas with long, moist autumns are required. It requires warmer temperatures and a milder climate than L. jacobaeae.

L. flavicornis has a native distribution area south of latitude 52 °N in England to east of longitude 5 ° in Siberia. It occurs in coastal areas of Morocco and Algeria, throughout Spain and southwest France. It co-exists with L. jacobaeae from south England to Paris, France. It primarily occurs in climates where winter temperatures average 0 °C, coinciding with the most southern limit of tansy ragwort.

British Columbia Experiences

L. flavicornis was released during the 1970’s in Nanaimo as 10% of a mixed population with L. jacobaeae. Despite repeated monitoring, no recoveries have been identified. It is probable that its most northern limit is the Coastal Douglas-fir biogeoclimatic zone.

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.

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.