Biological Control AgentRhinusa linariae Panzer

Invasive Plant Species Attacked: yellow toadflax (Linaria vulgaris), dalmatian toadflax (L. dalmatica) and narrow-leaved Dalmatian toadflax (L. genistifolia spp. dalmatica)

Type of Agent: Root feeding beetle (weevil)

Status

Primary 

Description and Biology

Adult:

The weevils are black, 2.5 - 3.0 mm long and convex-shaped.  Their bodies are covered with short dense grey hairs.  Their rostrums (nose) are arched and gradually tapered.  Adults emerge from overwintering when plants are 5 cm tall, usually late April and May and feed for three weeks before they begin to mate.  Mating occurs during the day, from morning to late afternoon and after one week the eggs are laid.  Females prepare oviposition locations by chewing holes in root tissue, usually near the crown.  The females oviposit the eggs singly into each pocket and cover them with excrement.  When suitable plant material is available, females will continue to lay for about two months (mid May to mid July).  Adults die after the oviposition period, usually by the end of July, and by the end of August, the new generation will be present.  In the field more males are found because females tend to hide out of site and in the soil. 

Egg:

The eggs are pale yellow, smooth surfaced, pear-shaped and measure 0.39 x 0.22 mm.

Larva and pupa:

There are three larval instars which develop in galls formed on roots and rhizomes.  The first instar is present until mid July, the second instar until the first week of August, and the final in mid August.  Pupation takes place within the galls.  Development from hatching to adult takes about three months.  By the end of August, all adults will have left the roots.  Fungal infections can attack the galls and cause mortalities during the larval and pupal stages.

Overwintering stage:

Adults that emerge in the summer overwinter in soil near the plants. 

Location and effectiveness of attack

When the females chew oviposition pockets, the plant reacts by producing a gall formation.  The larvae feeding in the galls may add to the development of further galls.  Several galls can fuse together creating masses.  Adult feeding on foliage and larvae feeding within galls contribute to using up nutrient reserves, causing stress and reduced plant vigour.

Predicted and native habitat

Rhinusa linariae tolerates cooler summer temperatures than R. antirrhini (Dalmatian toadflax bioagent) and establishes on yellow toadflax in a variety of situations.                      

R. linariae’s native distribution occurs throughout south-central and south-northern Europe.  It is found in Finland, Sweden, Germany, France, Austria, Czechoslovakia, Central Russia, and Poland.  In its native habitat it is common in grasslands and colline habitats, infrequent in the sub-alpine, and cannot be found in the alpine.

British Columbia Experiences

R. linariae was introduced into enclosed rearing tents in 1996 and the first field releases were made in 2001 near Kamloops.  Weevils were found at each site the following and subsequent years.  A site north of Kamloops experienced fire, excavation, and repeated compaction and still the weevil persists.  All the current treatments have been made in the Interior Douglas-fir biogeoclimatic zone (in a variety of sub-zones).  All field treatments are in locations that receive some to significant snow cover.  It has been found to exist on the same site as Mecinus janthinus, Calophasia lunula and the adventive strain of R. antirrhini found on yellow toadflax.  When collections are removed from the tented populations, few weevils are found the following year, subsequently to date, collections can only be made every other year.

Collection for redistribution

Not available for general distribution at this time.

Notes

Formerly known as Gymnaetron linariae and later spelled Gymnetron linariae before the genus name changed to Rhinusa.

They do not compete with the root feeding bioagents Eteobalea serratella and E. intermediella.  They can also exist with other bioagents including, M. janthinus, R. antirrhini, Brachypterolus pulicarius and C. lunula.

References

DeClerk-Floate, R., R. Nowierski, D. Schroeder and K. Jordon. 1994. Proposal to introduce Gymnetron linariae Panzer (Col.: Curculionidae) for the biological control of Dalmatian and yellow toadflax (Linaria dalmatica (L.) Mill. and L. vulgaris Mill.) in North America. Agric. Agri-Food Can., Dept. Entomol., MT State Univer., and Internat. Inst. Biol. Contr. 44 p.

MFR staff observations and comments