Biological Control Agent: Botanophila seneciella (Meade)
Invasive Plant Species Attacked: Tansy ragwort
(Senecio jacobaeae)
Type of Agent: Seed feeding fly
Status
Secondary
Description and Biology
Adult:
The dull grey adults are similar to houseflies. They have slightly clouded, clear
wings that extend beyond their body, ranging from 4 - 6 mm long. The female's abdomen
is conical, while the male's is narrow and both are covered with short hairs. Adults
emerge to coincide with floral bud formation of tansy ragwort. Females can be observed
walking over bolting plants investigating floral bud suitability. Appropriate buds used
for oviposition will be 3 - 4 mm in diameter. Egg laying coincides with floral development,
usually about one week after they emerge. Females deposit eggs individually near the
top of developing seeds between floral bracts. Adult life span is about 44 days.
Egg:
Eggs incubate for 3 - 4 days.
Larva and pupa:
Creamy white larvae emerge during June, July and early August. At high elevations,
emergence may be delayed until July. Three larvae instars feed for 26 - 29 days, developing
to 4 - 6 mm long while consuming part or all of the seeds. Early stages of seedhead attack
can be identified by observing a frothy secretion appearing from a small brown puncture dot.
Late stages are recognized by tufts of sticky brown florets or white pappus appearing from
between bracts. Infected seedheads, when opened, will expose the larvae or feeding evidence
- a hollow black cavity. Larvae mature in late summer, exit the seedheads and move to
the soil to pupate. A dark brown puparium is developed five days after the larvae enters
the soil and remains there until the following spring.
Overwintering stage:
Pupae overwinter within the soil.
Location and effectiveness of attack
Larvae feed in developing seedheads, often consuming all seeds and reproductive floral
parts. The best control has been on small isolated tansy ragwort patches where 30% of
flower heads are attacked. On large sites, the rate of attack plummets to 2%. Botanophila
seneciella , on its own, is unable to provide adequate control, but, contributes to the
overall desired affect when released onto sites with Longitarsus spp. or Cochylis atricapitana.
Predicted and native habitat
B. seneciella appears to have few site restrictions, establishing easily on tansy ragwort
growing in variable habitats. It has shown a preference for the open habitat of meadows,
forest openings and right-of-ways. Commonly it attacks plants in semi-shaded areas with
light canopy but avoids heavy shade. It fills a niche for areas less desired by other
agents, specifically Tyria jacobaeae. It has superior host seeking capabilities
and can easily locate isolated patches of tansy ragwort.
British Columbia Experiences
Origin:
The Canadian B.
seneciella populations came from French stock reared in California.
History:
Initially B. seneciella was introduced to BC into 1968. The lack of establishment
was blamed on poor synchronization of plant and agent. Releases were made again in 1970
in the Fraser Valley and today it is broadly dispersed in the Fraser Valley,
on Vancouver Island and also in the
Okanagan. It is the only tansy ragwort agent established beyond the lower mainland at
this time.
Habitat:
B. seneciella was originally released into the Coastal western hemlock
biogeoclimatic zone. It has since freely dispersed itself within the Coastal Douglas-fir, Coastal western hemlock,
and Interior Douglas-fir zones.
Field results:
B. senenciella is the only tansy ragwort biocontrol agent to
establish in the Okanagan. It was not intentionally released here and how
or when it arrived is not known. By mid to late September, some larvae
were still present in seedheads.
B. seneciella has dispersed itself freely enough to no longer warrant collections
for new releases in most situations. If releases are required, larvae transfers are best
suited for this agent by transplanting infested plants to new locations. Larvae can be
transferred in a variety of methods:
- Releasing 1000 to 1500 seedheads average 10 to 15 % attack and is sufficient to create
a new colony;
- Plants can be transplanted to new sites by moving infested plants just before peak
bud formation to ensure seed heads are infected. Transfers made too early or too late
can result in non-viable treatments;
- Infested plants can also be harvested in late summer and by keeping plant roots adequately
moist and their stems placed on sand allows the larvae to leave the heads and pupate in the
sand. The sand is then stored in a cool location and placed at the release point the
following spring; and
- Adults can also be swept as an alternative to larvae/pupae transfers. Adult collections
can occur in the early mornings when the temperatures are still cold. By keeping the
adult flies cool and dry they can survive up to one week before they must be released.
Notes
B. seneciella is also known as Hylemya seneciella Meade and Pegohylemyia seneciella.
It can co-exist with Longitarsus spp. and Cochylis atricapitana, but, is a poor
competitor against T. jacobaeae. Isolated small sites or widely spaced individual plants
are undesirable for T. jacobeae. B. seneciella will establish in these types of
infestations, subsequently avoiding competition and filling a specific niche.
It is not a strong invasive plant control agent but is the only one to establish east of
the Cascade Mountains.
References
Harris, P. 2003. Classical biological control of weeds established biocontrol agent Botanophila
seneciell a (Meade). Seed-head fly. Agriculture and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/abotasen_e.htm
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.
| 
