Biological Control Agent: Cystiphora sonchi (Bremi)

Invasive Plant Species Attacked: Perennial sow thistle (Sonchus arvensis)

Type of agent: Leaf gall forming fly

Status

Description and Biology

Adult:

Delicate adult flies are 5 mm long. Females can be identified by their red abdomen. They emerge at first morning light. Mating and oviposition begins immediately, but, they are also capable of unisexual reproduction. Females lay an average of 86 eggs onto the underside of rosette and stem leaves, often in a row formation, avoiding youngest and oldest leaves. The eggs are squeezed individually through pore openings (stomata), which are smaller than the egg. Adults remain non-feeding their entire life span which is 2 - 10 hours for males and 9 - 16 hours for females. In Canada there can be three generations/year which peak in June, August and September. Male/female ratio is 2:1.

Egg:

Eggs incubate for six days at 27°C (day) and 19°C (night). Green galls appear in five days.

Larva and pupa:

Larvae emerge six days after oviposition. On the eighth day, two days after their emergence, the galls (enlarged leaf cells), created during development, are visible from the upper leaf surface as the tissue above the larvae dies. On the tenth day, the leaf structure breaks down, becoming a food source for the larvae. After 10 - 17 days, mature larvae spin a white silken cocoon. Pupation occurs either in the gall or the larvae exit through the lower leaf surface stomata and move into the soil. Pupation is short, lasting 1 - 2 days.

Overwintering stage:

It is unknown at this time how Cystiphora sonchi prepares itself for overwintering. Some observations indicate mature larvae rest in cocoons until the following spring, resuming development when warm temperatures return.

Location and effectiveness of attack

Gall formations interrupt plant and leaf development and are a nutrient sink. High populations can weaken perennial sow-thistle.

Predicted and native habitat

C. sonchi has established in Alberta, Saskatchewan, Manitoba and Nova Scotia, but not in British Columbia, New Brunswick or Quebec. It has become widely distributed in Saskatchewan. Specific habitat requirements are not known at this time.

It is commonly found in sunny locations throughout its European habitat. Its native distribution includes areas between Scotland and western Russia and from Finland to south Italy.

British Columbia Experiences

Origin:

C. sonchi released in BC originate in Austria from populations reared on Sonchus oleraceus.

History:

C. sonchi was introduced into the Fraser Valley in 1984. A second treatment was made in the northern interior near Telkwa in 1992. No establishment has been found at either location.

Habitat:

British Columbia preferences are not known. Treatments have been made into the Coastal Douglas-fir/Coastal western hemlock and Sub-boreal spruce biogeoclimatic zones. No evidence of establishment was found at either site. C. sonchi is widely distributed in Saskatchewan, therefore, it may be possible to establish populations in similar climates in BC.

Field results:

In 2008, the release in northern BC was monitored, but no evidence of galls were found.

Collection for redistribution

Not available for general distribution at this time.

Notes

Larvae are susceptible to high parasitic attack by Aprostocetus spp near atticus Graham. High parasitism may be partially responsible for the bioagents ineffectiveness.

A greenhouse pest, Thrips tobaci is attracted to the galled area and its feeding on the gall is fatal to the larvae. The feeding thrips indicate the galls are a nutrient sink.

A study in Russia determined that seed production was reduced by 35 - 85% when C. sonchi was combined with other insects.

References

Harris, P. and D. P. Peschken. 2005. Classical biological control of weeds established biocontrol agent Cystiphora sonchi (Bremi). Leaf-gall midge. Agric. Agri-Food Canada. January 11, 2006. http://res2.agr.ca/lethbridge/weedbio/agents/acyson_e.htm

MFR staff observations and comments

Peschken, D.P. 1982. Host specificity and biology of Cystiphora sonchi (low) (Diptera: Cecidomyiidae), a candidate for the biological control of Sonchus species. Entomphaga 27(4) 405-415.