Biological Control Agent: Cyphocleonus achates (Fahr.)
Invasive Plant Species Attacked: Spotted
knapweed (Centaurea biebersteinii) and diffuse
knapweed (C. diffusa)
Type of agent: Root feeding beetle (weevil)
Status
Secondary
Operational Field Guide
Description and Biology
Adult:
The weevils measure 0.8 - 1.75 cm and at first have dark reddish-brown soft bodies.
In a few days their bodies harden and they become grey-brown. Their colouring allows
them to camouflage on dried plants, floral bracts and soils. Females have a rounded abdomen
while the males are flattened. They are rapid walkers which compensates for their inability
to fly. Adults emerge from roots in mid July; peak in August, then taper off into September.
The earliest quantity of emerging weevils has a higher ratio of males, later the ratio becomes
equal, and near the end of the season more females are present. Mating begins within
one or two weeks of emergence and egg laying begins in August. Females mate repeatedly
and oviposit an average of 45 eggs over their entire 10 week life span. The procedure
to lay each egg takes about 25 minutes to complete. Females excavate head first, 10 -
20 mm into soft soil and chew an attachment location on the plant crown. They then back
out and reverse into the site to deposit a single egg, cementing it in place with soil particles.
Usually the females will fill the excavation before moving on to repeat the process.
If the females do not backfill, another female will often use the prepared site to oviposit
another egg.
Egg:
The oval eggs are 1.76 x 1.24 mm. Initially, they are white or pale yellow and darken during
incubation, which takes 10 - 12 days.
Larva and pupa:
The larvae are plump, creamy white or yellowish, with large, light brown head capsules.
Similar to most weevils, they retain a "C" shape. There are four larval instars.
Upon hatching, new larvae mine inward to the root core. The first two instars feed within
roots until fall and then rest overwinter and resume feeding the following spring. Third
and fourth instar causes the root to swell and enlarge. Several larvae on one root create large
linked formations, 2 - 4 cm long x 1 cm wide. Pupation occurs in late spring or early
summer, lasting about two weeks. New adult weevils chew through the root and crawl to
the surface.
Overwintering stage: 
Second instar larvae overwinter in the root.
Location and effectiveness of attack
Larvae mine the plant roots which notably reduce the plants ability to dispense energy
used to produce shoot growth. Studies indicate that two larvae/spotted knapweed rosette
reduces shoot biomass by 65%. Larvae feeding cause plants to become shortened, producing
fewer flowers and less seeds. Adult feeding on leaves, especially young leaves, reduces
plant vigour. As plants become smaller or die, more soil surface becomes exposed, increasing
heat absorption which further enhances Cyphocleonus achates - preferred environment.
Once new weevils leave the root, their exit holes allow an entry point for secondary attacking
pathogens.
Predicted and native habitat
C. achates prefers hot and dry habitat, with loose well drained coarse soils.
It establishes in undisturbed bunchgrass habitat, favouring bare soil surfaces where grasses
do not crowd the target plants. It shows a preference for spotted knapweed over diffuse
knapweed. Sites need to be somewhat large with a corridor of plants for it to disperse
to by walking.
Its native distribution includes areas in eastern and southern Europe and Asia Minor.
It is found in the former Czechoslovakia, Austria, Hungary, Romania, Bulgaria, Greece, Turkey,
Syria and the former USSR.
British Columbia Experiences
Origin:
C. achates released in BC originate from Austria, Hungary and
Romania.
History:
C. achates was first introduced to BC in 1987. This first shipment was released
into rearing tents in Kamloops, open rearing plots at Castlegar and a field release in the
south Okanagan. In 1988, an open field release made in Kamloops became a collection source
in 1991. Over time several sites became premium collection sources, producing thousands
of adults for redistribution. In 10 years (1987 - 1997) 18,487 weevils had been collected
for redistribution. In 1996, BC shipped 529 weevils to Brocket, Alberta for a field release, but
there has been no further contact to determine the status of this site.
Assisted redistribution is still ongoing in BC.
Habitat:
C. achates has been released into the Bunchgrass, Coastal Douglas-fir,
Coastal western hemlock, Engelmann spruce-subalpine-fir, Interior cedar-hemlock, Interior Douglas-fir, Montane spruce, Ponderosa
pine, and Sub-boreal spruce biogeoclimatic zones. C. achates is found established
and dispersed in all these zones except the Montane spruce and Sub-boreal
spruce.
Field results:
C. achates successfully establishes with other bioagents, however, when competition becomes heavy, its population density seems to decline.
It has been found co-existing in sites with three other root feeders, Agapeta zoegana , Pterolonche
inspersa and Sphenoptera jugoslavica , and the seed feeders - Larinus minutus , L.
obtusus , Urophora affinis , U. quadrifasciata and Metzneria paucipunctella ,
and the stem/leaf rust Puccinia jaceae. C. achates mating is not observed before the first week of August and egg laying
follows in the third week.
Hand picking adults off plants allows for the immediate sorting of sexes if required.
If collection occurs when the sex ratio is in favour of the males, efforts are not as efficient
as release sites will not receive as many ovipositing females. Collection is best done
when the ratio is either equivalent or favours the females. Care must be taken, however,
to not collect too late in their season as females would have already laid their eggs.
Hand collecting is rapid and successful once the technique and weevil behaviour is learned.
Adults congregate on host plants and other vegetation, often in pairs. Shadows and plant
disturbance causes them to drop and feign death. They will move away from potential danger
by moving behind stems and circling out of view. Sweeping for adults can be done, but
increases the chance of damaging the adults.
Notes
C. achates can exist with A. zoegana and the two work better in conjuction
than on their own. A. zoegana prefers dense knapweed stands and their attack decreases
the plant size, which exposes more soil surface which results in warmer soil temperatures and
preferred C. achates habitat.
References
Harris, P. 2005. Classical biological control of weeds established biocontrol
agent Cyphocleonus achates (Fahr.). Root-core weevil. Gov. of Can., Agricul.
Agri-Food Canada. February 7, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/acypach_e.htm
Mason, P. G. and J. T. Huber, (editors). 2002. Biological control programmes
in Canada, 1981-2000. CAB International.
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.
Province of British Columbia. 1998. Operational field guide to the propagation
and establishment of the bioagent Cyphocleonus achates (knapweed root weevil). Min.
For., For. Practices Br., Range Sec., Noxious Weed Control Program. 30 p.
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