Biological Control Agent: Hylobius transversovittatus Goeze

Invasive Plant Species Attacked:  purple loosestrife (Lythrum salicaria L.)

Type of agent: Root feeding beetle (weevil)

Status

Description and Biology

Adult:

Hylobius transversovittatus are red coloured, stout weevils that measure 8 – 13 mm long.  The adults will appear when plants are about 20 cm tall and will be present from April through October.  They remain nocturnal, feeding at night until hibernation.  Adults are long lived, often two or three years or more.  They are slow to populate and will produce a single generation every one or two years.  The adults that emerge by mid August will oviposit the same year, those emerging later will overwinter.  Females deposit the eggs in the soil near the host plants and occasionally onto plant stems just above the soil.  During the yearly oviposition cycle, each female will lay up to 100 eggs, however, usually only one or two are laid each day.  The females can lay up to 300 eggs over their life span.  Congregations of adults are common in the field environment. 

Egg:

The pale yellow, oval eggs hatch within two weeks.

Larva and pupa:

The larvae are cream coloured with dark brown head capsules.  They bare a resemblance typical to those of other beetles/weevils by maintaining a crescent or ‘C’ shape.  The larvae hatching from eggs laid in the soil feed on root hairs and then burrow into the roots.  Larvae that hatch from eggs laid on the stem mine the shoots before moving down to the roots.   Root feeding can continue for two years.  Larvae development will be prolonged to two years if the plants become flooded.  During each period of flooding, larval development is interrupted, and resumes when the water subsides.  Mature third instars move to the upper portion of the root crown where pupation commences.  The duration from egg to adult takes one or two years.

Overwintering stage:

H. transversovittatus can overwinter in any of its life cycle stages: as eggs in the soil or plants; as larvae or pupae in roots; or, as adults in soil litter.

Location and effectiveness of attack

Larvae feeding may cause death to attacked plants.  Plants with small rootstocks can be killed within two years when attacked by two or more larvae.  Large rootstocks require a higher number of larvae to achieve the same result.  Adult feeding on leaves produce ragged leaf margins. 

Predicted and native habitat

H. transversovittatus is capable of tolerating a wide variety of habitats and environmental conditions.  Sites free from prolonged or frequent flooding are best suited.   H. transversovittatus has excellent host plant searching capability, which enables this agent to disperse easily to create new colonies.   

In its native distribution in Scandinavia it is most effective on sites not controlled by Galerucella spp.

British Columbia Experiences

A single release of H. transversivottatus was made in 1994 at the lower mainland in a tidal flat, within a protected ecological reserve. The treatment was made in July and during this same year high tides and a severe storm hit the site causing extreme devastation.  There has been no recovery of H. transversovittatus since its release.

Collection for redistribution

Not available for general distribution at this time.

Notes

H. transversovittatus is difficult to handle and expensive to rear.  Plant vigour and density controls the bioagent population. 

References

Blossey, B. and D. Schroeder.  1991.  Study and screening of potential biological control agents of purple loosestrife (Lythum salicaria L.).  Final Report.  Intern. Inst. of Biol. Control.  European Station, Delemont, Switzerland.  41 p. 

Lethbridge Research Center.  2005.  Classical biological control of weeds established bioagent Hylobius transversovittatus.  Gov. of Can., Agriculture and Agri-Food Canada.  January 30, 2007.  http://res2.agr.ca/lethbridge/weedbio/agents/ahyltra_e.htm  

Mason, P. G. and J. T. Huber, (editors).  2002.  Biological control programmes in Canada, 1981-2000.  CAB International.  

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.  

Wilson, M. L., M. Schwarzlaender, B. Blossey, and C. Bell Randell.  2004.  Biology and biological control of purple loosestrife.  Forest Health Enterprise Team, USDA.  78 p.