Biological Control Agent: Agapeta zoegana L.
Invasive Plant Species Attacked: Spotted
knapweed (Centaurea biebersteinii) and diffuse
knapweed (Centaurea diffusa)
Type of Agent: Root
feeding moth
Status
Secondary
Operational Field Guide
Description and Biology
Adult:
Adult moths are bright yellow and black. They are 1 - 2 cm long and have a wingspan that
measures 1.5 - 2.3 cm. Forewings are bright yellow with brown-black markings; hindwings are
dark grey. The females have a larger and more rounded abdomen than the males. The males have
a pair of clasping pincers at the end of their abdomen. Adults emerge from roots during mid
June to mid August and begin to mate and lay eggs within 24 hours. Females oviposit 66 - 185
eggs individually or in groups of two or three onto leaves or stems close to the crown, selecting
plants with a root diameter of 2.4 mm or larger. Temperatures between 18 - 30°C are best for
mating. Cool, windy days will delay oviposition. Adults live 10 to 14 days.
Egg:
Eggs are initially white and turn yellow-red after four days. They are flattened, oval
shaped, measuring 0.75 mm x 0.45 mm. With magnification, a network of meshed lines can be observed
on the outer egg surface. Eggs hatch in seven to ten days.
Larva and pupa:
The larvae are segmented, with white bodies and brown heads. Newly hatched larvae move
to the root crown to begin feeding. The larvae develop through six instars. The first through
fourth instars mine about 10 cm of the taproot over 40 - 45 days. As they mine the outer root
layers, they produce a whitish web tunnel that encloses around the larvae as they create a
spiral trail downward before they return towards the top of the root. If they require additional
food, the larvae can move through the soil to adjacent roots within 10 cm. In 70 days the larvae
will be mature in its sixth instar. Pupation takes about eight weeks which occurs the following
spring within the webbing. Multiple larvae can exist on a single root.
Overwintering stage:
It will overwinter in any larvae instar within the root.
Location and effectiveness of attack
Agapeta zoegana larvae feed on the outer layers of the root, creating spiral tunnels
which can kill small plants and prevent the flowering of larger ones. When the larvae enter
the root, they often damage the vegetative stem bud, causing the plant to send up multiple
short stems instead of a single bolt. Plants may become susceptible to secondary insect or
pathogen attack.
Predicted and native habitat
A. zoegana is common to the mesic, cooler areas where knapweed grows. Often it is
associated with sites that have moderate humidity and temperatures within the Bunchgrass and
Ponderosa pine biogeoclimatic zones. It can tolerate cold winter temperatures, but, it requires
a long growing season. The literature states that sites over 1000 m may not allow sufficient
time for development. Suitable host plants have 2.4 mm diameter roots growing in undisturbed
locations that are not mowed, grazed or cultivated.
Its native distribution includes the former Yugoslavia, eastern Rumania, western Hungary
and eastern Austria. Small populations occur in the Upper Rhine Valley, but, it is absent
in the Swiss Valais.
British Columbia Experiences
Origin:
The A. zoegana populations released in BC originate in Europe.
History:
The first A. zoegana release was made in 1982. Since then, thousands of adult moths
have been collected and redistributed throughout the province. in 1998
A. zoegana was designated to secondary status. Assisted
redistribution is ongoing. 
Habitat:
Releases have occurred in the Bunchgrass, Coastal Douglas-fir, Coastal western hemlock,
Interior cedar-hemlock, Interior Douglas-fir, Montane spruce, Ponderosa pine and Sub-boreal
spruce biogeoclimatic zones. Establishment and dispersal has been found throughout each of
these with the exception of the Montane spruce and Sub-boreal spruce zones.
Field results:
A. zoegana is well dispersed in the southern interior and can be
seen frequently from mid June through mid August. Recently, observations
indicate, as A. zoegana disperses its density declines. Many larvae
can be found on a single root, for example, 56 A. zoegana larvae
were found on a large root (over 20 cm long). Twenty-eight Cyphocleonus
achates larvae were also present on this same root
Using light suction, adults can be aspirated head first into prepared collection containers. Peak
emergence periods are in early mornings or evenings. Adults rest low on the plants or on the
soil surface during the day. Disturbing the plants will cause the adults to take short flights.
Notes
A. zoegana can exist with other root feeding biocontrol agents,
including Sphenoptera jugoslavica and Cyphocleonus achates.
References
Harris, P. 2007. Classical biological control of weeds established biocontrol agent Agapeta
zoegana (L.) Root-cortex feeder. Gov. of Can., Agriculture and Agri-Food Canada. January
15, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/aagapzoe_e.htm
MFR staff observations and comments
Muller, H., D. Schroeder and A. Gassmann. 1988. Investigations on Agapeta
zoegana Haw. (Lep.: Cochylidae), a possible biocontrol agent of spotted knapweed Centaurea
maculosa Lam. (Compositae) in Canada.
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.
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