Biological Control Agent: Hadroplontus litura (F.)
Invasive Plant Species Attacked: Canada thistle
(Cirsium arvense)
Type of agent: Stem feeding weevil
Status
Primary
Description and Biology
Adult:
The adult weevils are 3 - 4 mm long with a prominent long rostrum (nose). Their oval
bodies are completely covered with whitish hairs. Their upper back is dark grey to black
and marked with a distinct white 'T' or cross-like formation. When the weevils are on
the soil surface, the mottled markings camouflage them. In cool climates the adults appear
in early spring, from March to early June and will mate and produce a generation that emerges
in August and September. In the warmer areas, adults can remain active overwinter and
even year round from August through to the following May, June and occasionally July, depending
on habitat. In either case, the mating season remains the same. Oviposition starts
when thistle rosettes first appear in the spring, between March and mid May, and continues
for 4 - 6 weeks. The adult feeding on the leaves creates cavities where the female will
deposit the eggs. The females lay the eggs individually or in groups of 2 - 5 into the
cavities into plant tissue or in the mid-vein on the underside of leaves. Each of the
females will lay up to 120 eggs. The preferred oviposition hosts are smaller plants usually
up to 5 cm tall. When the plants reach beyond this height they become unsuitable.
Egg:
The eggs hatch in 5 - 9 days.
Larva and pupa:
The larvae are whitish coloured with light brown, pointed heads. There are three larval
instars which all occur within the plant. The first instar mines down the leaf vein and
into the plant stem. If the plant has already started to bolt, the larvae will mine up the
stem and feed on the inner pithy area. If the larvae enter non-bolting plants they will
mine downward and feed on the root crown and occasionally the root. The plants react
to the intruding larvae by producing "wound tissue" (a callus growth), which the larvae feed
upon. In vigorous growing plants, the callus can smother up to two larvae, but, if multiple
tunnels are present, the plant stem bases will swell and develop woody galls which instead
can kill the plant. By the end of the third instar the mature larvae move to the soil
to pupate in an oval cocoon made from soil particles. Pupation lasts two to three weeks
before new adults emerge in late summer and fall. Cool spring temperatures delay the
plants' bolt, maximizing larvae feeding and resulting in better plant control.
Overwintering stage:
In cool climates the adult will overwinter in the soil and leaf litter, however, in warm
climates there is no rest period and the adults can remain active all winter.
Location and effectiveness of attack
To kill the host plants, the larvae need to begin feeding in early spring before bolting
has started. Less impact is noticed if the attack comes after the plants have already
begun their active spring growth. The overall plant height is not affected by the larvae
mining. Secondary insects or pathogens attacking the plants are often more harmful than Hadroplontus
litura. When the larvae create the exit hole for pupation, they provide an entrance
for other organisms. Adult foliar feeding on upper and lower leaf surfaces creates a
window effect.
Predicted and native habitat
In North America, H. litura will establish on thick dense Canada thistle stands, preferring bare soil
surfaces between plants, and avoiding sites with competing plants. Spring flooding can be tolerated. Locations with long cool springs, which delay the
plants bolting, is better suited than those that encounter rapid gains in heat.
The weevils' native distribution occurs in Atlantic Europe, from the southern parts
of France to southern Scandinavia.
British Columbia Experiences
Origin:
H. litura populations released in BC originate from France, Germany
and Switzerland.
History:
H. litura was introduced to BC within a protected ecological
reserve in 1975 at the lower mainland and in 1987 a second treatment was made on
Vancouver Island. The earliest treatment site was noted to be established
within one year. In 1994, an attempt to transfer larvae/pupae infested
plants from Richmond to Kamloops was done.
Habitat:
H. litura has been released into the the Bunchgrass and Coastal
Douglas-fir biogeoclimatic zones. Establishment has been found in the
Coastal Douglas-fir zone. Efforts to determine the status of the site in
the Bunchgrass zone is ongoing.
Field results:
In 2008, the earliest release site was revisited. The area was fenced and most the thistle clipped and mowed. Despite the
mechanical control methods used here, a single adult was located. There is
a possibility that the agent dispersed to nearby thistle patches as the plants
became less abundant. In 2002, an unidentified dead
beetle pupae was found inside a plant root at the Kamloops site. At this same location,
in 2003 and 2004 stem mining and frass was observed. Foliar feeding,
stem tunnelling and one dead larva was found the following spring (2005).
The results are inconclusive at this time.
Not available for general distribution at this time.
Notes
Formerly known as Ceutorhynchus litura.
Studies have shown H. litura capable of infesting 80% of a Canada thistle site in
10 years and can disperse 9 km in 10 years.
In Ontario, H. litura was found in higher quantities on plants infested with
Puccinia punctiformis.
It is not known if the weevil prefers plants attacked with the rust, or, if the weevil may
be a vector. Plant density appears to decline when attacked by both H. litura and
P. punctiformis at the same time.
References
Harris, P. 2003. Classical biological control of weeds established bioagent Hadroplontus
litura (F.). Stem weevil. Agriculture and Agri-Food Canada. May 20, 2003.
http://res2.agr.ca/lethbridge/weedbio/agents/aceutlit_e.htm
Kelleher, J. S. and M. A. Hulme, (editors). 1984. Biological control programmes against
insects and weeds in Canada 1969-1980. Commonwealth Agricultural Bureaux.
MFR staff field 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.
Ralph, D. 2006. Personal comments. BC Min. of Agric. and Food.
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