Biological Control Agent:  Bradyrrhoa gilveolella (Treitschke)

Invasive Plant Species Attacked: Rush skeletonweed (Chondrilla juncea)

Type of agent: Root feeding moth

Status

Primary

Description and Biology

Adult:

Adult moths are 11 - 13 mm long and are creamy buff coloured with three brown bands that traverse their anterior wings.  Their wingspan is from 25 mm to 28 mm across.  The moths' emergence is variable depending on the climate.  Normally the first generation appears in May.  After adult emergence, egg laying occurs within 2-8 days onto the soil surface at the base of plants or onto stems.  The second generation appears in June to September.

Egg:

The eggs are 0.65 to 0.8 mm long and 0.45 wide.  At the time they are laid the eggs are creamy white and darken with age.

Larva and pupa:

The newest larvae have pink bodies and brown heads.  As the larvae develop they change to an ivory-cream colour.  Newly hatched larvae descend downward from the host plant by a silk thread and crawl over the soil surface to a plant.  Once in contact with the plant, they begin to feed into the stem base then move downward and attach themselves to the root.  The larvae continue to develop within loosely spun silk feeding tubes.  Generally there are one or two larvae/root, but as many as three to 10 can be found.  When mature, the larvae will measure 20-26 mm with a 1.6 - 2.6 mm wide head capsule.  The pupae develop below the soil surface within the feeding tubes.  Pupae are light brown with a smooth appearance.   Once pupation is complete, the emerging adults use the feeding tube to exit the root.

Overwintering stage:

In Russia, the second generation overwinters as dormant larvae.  In Greece, they also overwinter as dormant larvae, but, the generations are not as distinct because of the shorter winter.  Populations emerge earlier in Greece, starting in late April to early May.

Location and effectiveness of attack

Larvae feed on rootstock and dissect sections of the root which interrupts the flow of nutrients and reduces the plants- root reserves.  The larvae feeding also can destroy adventitious buds near the root crown.  The feeding reduces plant vigor, reproductive ability and can kill small plants.  The damage to larger plants causes them to be susceptible to pathogenic fungi.  Large plants can survive minor attack, but, heavy infested plants can be killed.

Predicted and native habitat

The preferred BC habitat is unknown at this time.

Bradyrrhoa gilveolella is native to southern Russia and northern Greece.  In Russia the climate has low to very low sub-zero temperatures with three months of hot summer and little precipitation.  In Greece, the habitat has mild wet winters and hot summers, with less than 500 mm of rainfall.  In their native habitat, they appear to prefer sandy soils.  Compacted soils are not suitable, even if sand is part of its composition.

British Columbia Experiences

Origin:

B. gilveolella released in BC were lab reared in Idaho from populations that originate from Lake Prespa, Greece. 

History:

B. gilveolella was first introduced to BC in July, 2007 at which time adult moths where released into two enclosed propagation tents in the north Okanagan.  This same year during early fall, larvae infested plants were transplanted into two more tents at this same location.

Habitat:

The B. gilveolella propagation tents are established in ideal rush skeletonweed habitat in the Interior Douglas-fir biogeoclimatic zone.  Reports indicate that the agent has not established well in the USA at this time. 

Propagation results:

By the time the shipment arrived from the United States, many of the moths had began ovipositing eggs into the shipping containers.  These eggs were returned to AAFC in Lethbridge and transferred onto potted rush skeletonweed host plants and held in growth chambers.  In September, the plants were returned to BC and transplanted into two additional propagation tents at the same north Okanagan location.  In August 2008, three adults emerged from the plots that had received the infested transplants (see Biocontrol News - March 2009).

Collection for redistribution

Not available for general distribution at this time.

Notes

Study notes indicate there to be 60% less flower production on release locations in Australia.

This is the first root feeding biocontrol agent for rush skeletonweed released into BC.

Open field releases in the United States have not shown any establishment, however, that may be due to widespread moth dispersal.

References

Littlefield, J.  2009.  Pers. Comm.

Littlefield, J. L., J. Birdsall, J. Helsley and G. Markin.  2000.  Supplemental report to -A petition for the introduction and field release of Chondrilla root moth Bradyrrhoa gilveolella for the biological control of rush skeletonweed in North America.

Horner, Tracey A.  2002.  Field release of Bradyrrhoa gilveolella (Lepidoptera: Pyralidae), for biological control of rush skeletonweed, Chondrilla juncea (Asteraceae).  USDA - APHIS, United States Department of Agriculture.  Government of the United States.

United States Department of Agriculture Forest Service.  2003.  RM-4151 - Ecology & management of northern rocky mountain forests. January 25, 2006.  http://www.fs.fed.us/rm/ecology/studies/biocontrol/rsw

Wikeem, Brian and Sandra Wikeem.  2005.  A petition for the introduction and field release of the Chondrilla root moth, Bradyrrhoa gilveolella (Treitschke) for the biological control of rush skeletonweed (Chondrilla juncea L.) in British Columbia, Canada.