Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

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Rhinocyllus conicus
(thistle-head weevil)

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Datasheet

Rhinocyllus conicus (thistle-head weevil)

Pictures

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PictureTitleCaptionCopyright
Thistle-head weevil (Rhinocyllus conicus); adult.
TitleAdult
CaptionThistle-head weevil (Rhinocyllus conicus); adult.
Copyright©Loke T. Kok/Virginia Polytechnic Institute and State University/Bugwood.org - CC BY 3.0 US
Thistle-head weevil (Rhinocyllus conicus); adult.
AdultThistle-head weevil (Rhinocyllus conicus); adult.©Loke T. Kok/Virginia Polytechnic Institute and State University/Bugwood.org - CC BY 3.0 US
Thistle head weevil (Rhinocyllus conicus); larvae and pupae (two pupae on right).
TitleLarva and pupae
CaptionThistle head weevil (Rhinocyllus conicus); larvae and pupae (two pupae on right).
Copyright©Mark Schwarzlander/University of Idaho/Bugwood.org - CC BY-NC 3.0 US
Thistle head weevil (Rhinocyllus conicus); larvae and pupae (two pupae on right).
Larva and pupaeThistle head weevil (Rhinocyllus conicus); larvae and pupae (two pupae on right).©Mark Schwarzlander/University of Idaho/Bugwood.org - CC BY-NC 3.0 US

Identity

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Preferred Scientific Name

  • Rhinocyllus conicus Froelich 1792

Preferred Common Name

  • thistle-head weevil

Other Scientific Names

  • Curculio conicus

International Common Names

  • English: thistle head weevil

Local Common Names

  • Australia: receptacle weevil; seed-head weevil
  • New Zealand: nodding thistle receptacle weevil

EPPO code

  • RHILCO (Rhinocyllus conicus)

Summary of Invasiveness

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Native to Europe and western Asia, R. conicus has been deliberately introduced to Canada in 1968 (Harris and Zwölfer, 1971; Harris, 1984); South America in 1980 (Feldman, 1997); Australia in 1989 (Woodburn and Cullen, 1993; 1995); and New Zealand in 1973 (Jessep, 1975; 1981) as a biological control agent for thistles in the genera Carduus,Cirsium and Silybum. Introduced populations were collected from different hosts and so included populations from both temperate and Mediterranean climates.

North America has a number of species of native thistle in the genus Cirsium that are susceptible to damage from R. conicus. As the impacts of R. conicus on some of them has been quite significant (Louda et al., 1990; 1995; Louda and Potvin, 1995; Louda 1998), and as some of these native thistles were already threatened,  R. conicus is now considered an invasive species within parts of North America (Louda et al., 1997). At the time of its release, the potential impact of R. conicus on native thistles was considered acceptable.

In regions other than North America, no vulnerable native or economically important plants occur within the host range of R. conicus. It is not a regulated pest in any country of introduction.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Coleoptera
  •                         Family: Curculionidae
  •                             Genus: Rhinocyllus
  •                                 Species: Rhinocyllus conicus

Notes on Taxonomy and Nomenclature

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Rhinocyllus conicus is a weevil, native to Europe and western Asia, that has been introduced into several countries as a biological control agent for some exotic invasive thistle species (Boldt and Kok, 1982). Rhinocyllus is a small genus of five species in the tribe Rhinocyllini. Rhinocyllini contains only one other genus, Bangasternus, which contains seven species (Zwölfer and Harris, 1984). All weevils from both genera are believed to feed in the capitula of Asteraceae species. R. conicus has eight synonyms (Hoffmann, 1956; Alonso-Zarazaga and Talamelli, 2011).

Allozyme and morphometric analysis of R. conicus, from the Atlantic coast to Israel, found two distinct groups (Klein and Seitz, 1994). The two groups, temperate and Mediterranean, correspond to differences in climate, and differ in their phenology of oviposition and physical appearance:  the Mediterranean group starts to lay about a month earlier than the temperate group and generally has a narrower body shape, although there is individual variation and overlap between the two groups. On this basis, and given the genetic divergence between groups, Klein and Seitz (1994) argued that R. conicus has two subspecies. They also argued that the Mediterranean group matches the morphological descriptions and climatic distributions of R. oblongusCapiomont (1873) and therefore that the status of this species needs further consideration.

Description

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Eggs are laid under frass caps on the external surface of the bracts of the pre-flowering capitulum. The four instars of larval development and pupation occur inside the capitulum. The adult is a typical ‘snout-beetle’, 6 (3-7) mm long. It is dark in colour with many clusters of vertical short, brown hairs that give it a ginger-speckled appearance. The hind wings are well developed as the insect is a strong daylight flier (Jessep, 1981).

Distribution

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The known distribution of R. conicus does not perfectly match the distribution of its main host plants in its native range, which suggests some apparent gaps in its native range may simply be because the host has been recorded but the pest has not. R. conicus is likely to have a largely continuous distribution around the Mediterranean corresponding to the distributions of its main host plants (see Hosts/Species Affected). 

Its true range in North America is likely to be greater than what has been recorded. Zwölfer and Harris (1984) stated that R. conicus ‘has been established in most parts of North America with a Carduus nutans problem’; C. nutans is known from nearly all of North America except 5 US states and 4 Canadian Provinces (USDA, 2013).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

IsraelPresentNative Not invasive Klein and Seitz, 1994
KazakhstanPresentNative Not invasive Zwölfer and Harris, 1984
KyrgyzstanPresentNative Not invasive GBIF, 2012
TurkeyUnconfirmed recordZwölfer and Harris, 1984R. oblongus present which may be the Mediterranean subspecies (Klein and Seitz, 1994)
UzbekistanPresentNative Not invasive GBIF, 2012

Africa

AlgeriaLocalisedNative Not invasive Zwölfer and Harris, 1984
LibyaLocalisedNative Not invasive Zwölfer and Harris, 1984
MoroccoUnconfirmed recordNative Not invasive Csiki, 1934Csiki states N Africa as part of the native range, and Morocco has suitable hosts
Spain
-Canary IslandsPresentNative Not invasive Alonso-Zarazaga and Talamelli, 2011

North America

Canada
-AlbertaDesrochers et al., 1988Pest host present
-British ColumbiaDesrochers et al., 1988Pest host present
-ManitobaIntroducedDesrochers et al., 1988
-Nova ScotiaIntroduced1968 Not invasive Desrochers et al., 1988Pest host present
-OntarioIntroduced1968 Not invasive Laing and Heels, 1978
-QuebecIntroduced
-SaskatchewanIntroduced1968 Not invasive Harris, 1981
USAPresentPresent based on regional distribution.
-AlabamaWidespreadIntroducedGassmann and Kok, 2002
-ArkansasLocalisedIntroducedMicinski and Cookson, 2011
-CaliforniaWidespreadIntroduced1971Andres and Rees, 1995Goeden 1995 for release date
-ColoradoWidespread Invasive Andres and Rees, 1995Based on impact on native thistles (DePrenger-Levin et al. 2010)
-DelawarePest host present
-District of ColumbiaPest host present
-GeorgiaWidespreadIntroducedGassmann and Kok, 2002
-IdahoWidespreadIntroduced1975Andres and Rees, 1995
-IllinoisWidespreadIntroducedGassmann and Kok, 2002
-IndianaWidespreadIntroducedGassmann and Kok, 2002
-IowaWidespreadIntroducedAndres and Rees, 1995
-KansasWidespreadIntroduced1975Andres and Rees, 1995
-KentuckyWidespreadIntroducedAndres and Rees, 1995
-LouisianaWidespreadIntroduced1975Andres and Rees, 1995
-MainePest host present
-MarylandWidespreadIntroducedAndres and Rees, 1995
-MassachusettsPest host present
-MichiganPest host present
-MinnesotaWidespreadIntroduced1975Andres and Rees, 1995
-MississippiPest host present
-MissouriWidespreadIntroducedAndres and Rees, 1995
-MontanaWidespreadIntroduced1969Andres and Rees, 1995
-NebraskaWidespreadIntroduced Invasive Andres and Rees, 1995Based on impact on native thistles (Louda et al. 1990)
-NevadaPest host present
-New HampshirePest host present
-New JerseyWidespreadIntroducedGassmann and Kok, 2002
-New MexicoPresentIntroducedUS Fish and Wildlife Service, 2010b
-New YorkWidespreadIntroducedGassmann and Kok, 2002
-North CarolinaWidespreadIntroducedGassmann and Kok, 2002
-North DakotaWidespreadIntroduced1975Andres and Rees, 1995
-OhioWidespreadIntroducedGassmann and Kok, 2002
-OklahomaWidespreadIntroduced1975Andres and Rees, 1995
-OregonWidespreadIntroduced1978Andres and Rees, 1995Goeden 1995 for release date
-PennsylvaniaWidespreadIntroducedAndres and Rees, 1995
-Rhode IslandPest host present
-South CarolinaPest host present
-South DakotaWidespreadIntroducedAndres and Rees, 1995
-TennesseeWidespreadIntroduced Invasive Andres and Rees, 1995Based on impact on native thistle in controlled studies, not natural populations (Wiggins et al. 2010)
-TexasWidespreadIntroducedGassmann and Kok, 2002
-UtahWidespreadIntroduced1975Andres and Rees, 1995
-VermontPest host present
-VirginiaWidespreadIntroduced1969Andres and Rees, 1995
-WashingtonWidespreadIntroduced1980sAndres and Rees, 1995
-West VirginiaWidespreadIntroducedGassmann and Kok, 2002
-WisconsinIntroduced1975Andres and Rees, 1995Based on impact on native thistle (Sauer and Bradley 2008)
-WyomingPresentIntroduced1975Andres and Rees, 1995

South America

ArgentinaWidespreadIntroduced Invasive Feldman, 1997

Europe

AlbaniaWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
BelgiumWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
BulgariaPresentNative Not invasive Alonso-Zarazaga and Talamelli, 2011
CroatiaWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
Czech RepublicWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
FranceWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
GermanyWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
GreeceLocalisedNative Not invasive Alonso-Zarazaga and Talamelli, 2011Mainland & Crete
HungaryWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
ItalyWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011Including Sicily & Sardinia
LuxembourgLocalisedNative Not invasive Alonso-Zarazaga and Talamelli, 2011
MoldovaPresentNative Not invasive Alonso-Zarazaga and Talamelli, 2011
NetherlandsLocalisedNative Not invasive Alonso-Zarazaga and Talamelli, 2011
NorwayPresentNative Not invasive GBIF, 2012
PolandWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
PortugalLocalisedNative Not invasive Alonso-Zarazaga and Talamelli, 2011
Russian FederationPresentPresent based on regional distribution.
-Southern RussiaPresentNative Not invasive
SlovakiaWidespreadNative Not invasive Alonso-Zarazaga and Talamelli, 2011
SpainLocalisedNative Not invasive Alonso-Zarazaga and Talamelli, 2011
-Balearic IslandsUnconfirmed recordZwölfer and Harris, 1984R. oblongus present which may be the Mediterranean subspecies (Klein and Seitz, 1994)
SwedenPresentNative Not invasive Alonso-Zarazaga and Talamelli, 2011
UKPresentAlonso-Zarazaga and Talamelli, 2011; Denton, 2011
UkrainePresentNative Not invasive GBIF, 2012

Oceania

AustraliaPresentPresent based on regional distribution.
-New South WalesWidespreadIntroduced Not invasive Woodburn and Cullen, 1995
-VictoriaLocalisedIntroduced Not invasive
New ZealandWidespreadIntroduced Not invasive Jessep, 1981

History of Introduction and Spread

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R. conicus was first considered as a biological control agent for the exotic nodding thistle Carduus nutans by Canada. In 1968 the weevil was introduced to Saskatchewan and Ontario from Alsace, France, and the Rhine valley, Germany. The weevil proved an effective agent against C. nutans and also attacked another exotic plumeless thistle, C. acanthoides. From Saskatchewan and Ontario R. conicus was moved and released into the USA, in Virginia and Montana, in 1969. Again it proved effective against the target and was spread widely throughout the country.

Populations of the weevil from Italy, which may be a separate ecotype (Zwölfer and Harris, 1984) or subspecies (Klein and Seitz, 1994), were released in California on both variegated or milk thistle Silybum marianum and slender or Italian thistle Carduus pycnocephalus in 1971 and 1973 respectively, but proved ineffective (Goeden and Ricker, 1977; 1978).

New Zealand imported and released weevils from Canada in 1973, which proved effective against C. nutans in New Zealand.

Argentina released weevils from the USA in 1980, largely against C. acanthoides, a plant which has caused considerable damage in Argentina (Feldman, 1997).

In 1989 Australia released three populations of R. conicus, from New Zealand, southern France and Italy, into the state of New South Wales to counter C. nutans there (Woodburn and Cullen, 1993; 1995; Cullen and Sheppard, 2012), but only the New Zealand and French populations spread widely. Overall, R. conicus was less effective in Australia due to asynchrony with its host. Populations of the weevil from south-west France were released against spear thistle Cirsium vulgare in the state of Victoria in Australia in 1989, but establishment has been poor since (Sagliocco et al., 2012).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Argentina USA 1980 Yes No Feldman (1997)
Australia France 1989 Biological control (pathway cause) Yes No Woodburn and Cullen (1995)
Australia New Zealand 1989 Biological control (pathway cause) Yes No Woodburn and Cullen (1995)
Canada France 1968 Biological control (pathway cause) Yes No Harris (1981) Effective agent
Canada Germany 1968 Biological control (pathway cause) Yes No Harris (1981) Effective agent
New Zealand Canada 1973 Biological control (pathway cause) Yes No Jessep (1981) Effective agent
USA Canada 1969 Biological control (pathway cause) Yes No Andres and Rees (1995) Effective agent
USA Italy 1969 Biological control (pathway cause) Yes No Andres and Rees (1995) Effective agent

Risk of Introduction

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The risks of the introduction and spread of R. conicus to other regions is limited, as it is specific to a few genera of host plants and has only left its native range through deliberate release as a biological control agent. Further deliberate introductions seem unlikely as there are few other countries where the thistle host plants are serious weeds.

The negative impacts of this insect are restricted to North America as this is the only continent with native (or commercial) plants that are susceptible to attack. R. conicus is probably already in most parts of the USA where its target hosts grow, so risks of further spread within the USA are only to regions with susceptible native thistles but without any of the relevant exotic thistles. To reduce risk of spread within the USA, R. conicus is now banned from inter-state movement.

Habitat

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R. conicus is restricted to the habitats and regions where its host plants are found (see Hosts/Species Affected). The host plants are found in pastures and disturbed sites, like roadsides, in temperate and Mediterranean climates in Europe, North Africa, Western Asia, North America, southern South America, south-eastern Australia and New Zealand.

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
 
Terrestrial – ManagedManaged grasslands (grazing systems) Principal habitat Natural
Industrial / intensive livestock production systems Secondary/tolerated habitat Natural
Disturbed areas Secondary/tolerated habitat Natural
Rail / roadsides Secondary/tolerated habitat Natural
Urban / peri-urban areas Secondary/tolerated habitat Natural
Terrestrial ‑ Natural / Semi-naturalNatural grasslands Secondary/tolerated habitat Natural
Riverbanks Secondary/tolerated habitat Natural

Hosts/Species Affected

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North America has about 90 species of native thistle in the genus Cirsium (USDA, 2013). Susceptibility of these species to R. conicus is related to a) their proximity to exotic host thistle populations on which this weevil is found, and b) the degree to which flowering phenology is synchronous with the reproductive cycle of R. conicus (Russell et al., 2007). A number of rare and threatened native Cirsium species in North America have been documented: these include C. canescens Nutt. (Louda et al., 1990; Arnett and Louda, 2001), C. undulatum Nutt. (Maw, 1982), C. ownbeyi S.L. Welsh (DePrenger-Levin et al., 2010) and C. hillii (Canby) Fernald (Sauer and Bradley, 2008). Turner et al. (1987) listed another twelve species of native Cirsium thistles in California from which R. conicus has been reared. Maw (1982) also found eggs on the native C. flodmanii (Rydb.) in Canada.

Growth Stages

Top of page Flowering stage, Fruiting stage

Symptoms

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R. conicus lays frass-covered eggs on the exterior involucral bracts of immature inflorescences of its host. The larvae hatch and bore into the receptacle of the capitulum, destroying the reproductive surface from which achenes develop. A single larva destroys on average 26 seeds (Sheppard et al., 1994).

List of Symptoms/Signs

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SignLife StagesType
Fruit / internal feeding
Inflorescence / dieback
Inflorescence / dwarfing; stunting
Inflorescence / internal feeding
Seeds / discolorations
Seeds / empty grains
Seeds / fused together
Seeds / shrivelled
Whole plant / internal feeding

Biology and Ecology

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Genetics

The various groups and ecotypes of R. conicus have been described but not been fully understood genetically. Some may be subspecies. Populations from different regions and hosts have distinct host preference profiles and capacities to differentially exploit different thistle hosts (C. nutans, C. pycnocephalus, C. vulgare (Savi) Tenore and Silybum marianum Gaert.) (Unruh and Goeden, 1987). Populations from Onopordumacanthium have also been described (Zwölfer and Harris 1984). More work is needed to better understand the genetic patterns underlying these differences and to see if the different ecotypes show any degree of reproductive incompatibility.

Reproductive Biology

R. conicus is a univoltine to partly bivoltine weevil. Adult females lay about 200 (54-360) eggs which take about a week to hatch. There are four larval instars which feed and pupate internally in the capitulum, in a hard black ovoid cell that resembles a gall. Pupation takes up to two weeks but the immature adults stay in the cells several weeks. Development from egg to adult takes about seven weeks, but may be shorter in Mediterranean climates. Newly emerged adults seek aestivation sites in summer in Mediterranean regions, whereas in temperate regions a second partial generation takes place. In late summer and in autumn the adults seek overwintering sites away from their hosts. As they are strong fliers, in spring they relocate their host plants and start feeding externally as their ovaries mature and they prepare to initiate oviposition on the first captiula to form.

Physiology and Phenology

This weevil only has a partial second generation in more temperate climates (Gassmann and Kok, 2002); however, in Tennessee and Georgia, R. conicus was observed to complete one generation and then not feed on thistles until the following spring (Wiggins, 2013, personal communication). Zwölfer and Harris (1984) considered that day-length determines second generations, so that new adults experiencing increasing daylength will start a second generation on flower heads of their host (mainly Carduus nutans) which developed later in the season. The first generation is very much skewed towards host captiula produced in spring (Cullen and Sheppard, 2012), which are also the largest; this means that later, smaller capitula receive proportionally fewer eggs. The capacity for a second generation is assisted by a longer flowering period of the host in temperate wetter summers.

In the Mediterranean region, where R. conicus also uses the hosts C. pycnocephalus, C. tenuiflorus and S. marianum, the hot dry summer means the hosts have a relatively early, but shorter flowering period, meaning R. conicus starts ovipositing earlier than in temperate regions, but only has time for one generation before their hosts stop flowering and adults need to seek aestivation sites. These differences relate to the different ecotypes by both region and host, and allow this species to persist under a broader range of hosts and climates.

In the exotic range these differences in phenology by ecotype are maintained with little evidence of quick synchronization to new conditions (Cullen and Sheppard, 2012), suggesting the ecotypes are phonologically distinct and not a phenotypically plastic strategy of survival. Effectiveness as a biocontrol agent and the impact of R. conicus on native thistles in the exotic range are determined by the degree of synchrony between the weevil oviposition and flowering of available potential hosts (Goeden and Ricker, 1985). Therefore the native thistles most impacted on by R. conicus tend to be those that flower early in the growing season. As a biological control agent it has proved more effective in temperate regions and this may be in part because the populations of the weevil introduced into these regions have a partial second generation.

Longevity

Adults live up to 12 months.

Activity Patterns

Mediterranean-adapted populations undergo aestivation through the dry summer months. All populations hibernate through the cold months and migration tends to occur in spring, when the adults seek host populations having emerged from their hibernation sites. Once the adults have located host populations they become much more sedentary.

Population Size and Density

Population size is determined by the abundance of their principal host plants, but can range up to tens of individuals per square meter in spring when there are dense populations of host plants.

Nutrition

Nutrition is restricted to known host plants in the genera Carduus, Cirsium, Silybum and Onopordum.

Associations

This weevil is one of a diverse community of insects found in the capitula of its host plants in its native range (Sheppard et al., 1991; 1994). Other insects in this community tend to be active later in the flowering periods, but competition in the captula is quite intense. In the exotic range, the insect community is largely limited to other species that have been introduced as biological control agents in the exotic hosts (e.g. Woodburn, 1996); however, amongst the native thistles R. conicus competes in the developing capitula with native insects, particularly tephritid seed flies, and may locally threaten the population viability of such flies (Tatyana and Louda, 2011).

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Air Temperature

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Parameter Lower limit Upper limit
Mean maximum temperature of hottest month (ºC) 25 40
Mean minimum temperature of coldest month (ºC) -20 10

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Bracon mellitor Parasite
Bracon urinator Parasite Larvae not specific Native range N
Campoplex polychrosidis Parasite
Exeristes roborator Parasite Larvae not specific Native range N
Lyrcus maculatus Parasite California
Lyrcus maculatus
Macroneura vesicularis Parasite California Carduus nutans
Microdontomerus anthonomi Parasite USA; California Carduus nutans
Nealiolus curculionis Parasite
Neocatolaccus tylodermae Parasite USA; California Carduus nutans
Pterandrophysalis levantina Parasite Eggs to species Native range N
Strongygaster triangulifera Parasite
Xysticus californicus Predator

Notes on Natural Enemies

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R. conicus is attacked by many different species of parasitoid in its native range (Zwölfer and Harris, 1984). The impact of these parasitoids on native R. conicus populations can be very significant, with particularly high levels of egg parasitism. Indeed, it appears that R. conicus lays more eggs on early capitula than the individual captulum can support, as in the native range parasitoids often kill a proportion of eggs; however, this over-laying of eggs can mean that capitula in the exotic range may wilt under the attack levels of R. conicus, leaving all larvae dead (Cullen and Sheppard, 2012). R. conicus in its native range can also be quite heavily attacked by Nosema, a microsporidian parasite (Woodburn and Cullen, 1995; Cullen and Sheppard, 2012). In its exotic range R. conicus has also attracted parasitoids (Zwölfer and Harris, 1984; Wilson and Andres, 1986), but at quite low rates.

Means of Movement and Dispersal

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It does not seem that R. conicus has managed to spread to new regions unaided. Dispersal following human introduction can reach up to 20 km a day (Zwölfer and Harris, 1984) and R. conicus can quickly spread over a large area (Hodgson and Rees, 1976). However, dispersal only takes place in spring and in the absence of suitable nearby hosts.

Impact Summary

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CategoryImpact
Economic/livelihood Positive
Environment (generally) Negative

Economic Impact

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The economic benefits of R. conicus as a biological control agent against the exotic thistle Carduus nutans have been very significant in Canada, the USA and New Zealand. This agent has been less effective in Australia. The size of these economic benefits has not been quantified financially for any of these countries; however, the success of control due to other agents in Australia has been estimated at $69M for whole of life (Page and Lacey, 2006). Based on the relative distribution and abundance of C. nutans in these other countries, the benefits to New Zealand resulting from the impacts of R. conicus are likely to be a similar order of magnitude to Australia, while in North America the benefits are likely to be very much higher, perhaps an order of magnitude higher or more.

Environmental Impact

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Impact on Biodiversity

R. conicus reduces seed production of the native North American thistle species it is able to attack (Turner et al., 1987; Louda, 1998). This can have a direct impact on population density of the affected species when they are seed limited (Louda et al., 1997). The extent of the impact therefore relates to the degree to which the thistle populations are already threatened by other factors, and the level of damage R. conicus is able to cause, given the proximity and abundance of its normal hosts and the degree of synchrony in flowering between these and the native thistles (Russell et al., 2007).

When present in high densities R. conicus may also impact native insects in the capitula of the native thistles (Tatyana and Louda, 2011). Some native thistle populations may be pushed to extinction by this weevil under some circumstances (Louda and Potvin, 1995).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Cirsium canescensNational list(s) National list(s)USALouda et al., 1990
Cirsium ownbeyiNational list(s) National list(s)USADePrenger-Levin et al., 2010
Cirsium pumilum var. hilliiNational list(s) National list(s)USASauer and Bradley, 2008
Cirsium pitcheri (Pitcher's thistle)NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened speciesIllinois; Indiana; Michigan; WisconsinHerbivory/grazing/browsingUS Fish and Wildlife Service, 2010a
Cirsium vinaceum (Sacramento Mountains thistle)NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened speciesNew MexicoHerbivory/grazing/browsingUS Fish and Wildlife Service, 2010b

Social Impact

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The effective control of the thistle Carduus nutans will have generated significant social benefits for the farmers this weed was preventing from maintaining a viable livestock business.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Highly mobile locally
  • Has high reproductive potential
  • Gregarious
Impact outcomes
  • Host damage
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
  • Negatively impacts animal/plant collections
Impact mechanisms
  • Competition
  • Herbivory/grazing/browsing
  • Interaction with other invasive species
  • Parasitism (incl. parasitoid)
Likelihood of entry/control
  • Difficult to identify/detect as a commodity contaminant

Uses

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The economic and social benefits of R. conicus are due to its effective control of the invasive thistle Carduus nutans, which impacts on the grazing and pastoral industries and farmer livelihoods.

Similarities to Other Species/Conditions

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The other four species in the genus Rhinocyllus also feed in the capitula of members of the tribe Cardueae (in the Asteraceae). These are R. oblongus Cap. (found in Spain, Italy, Greece and Turkey), R. depressirostris Boh. (southern Russia), R. remaudieri Hoffm. (Iran) and R. schoenherri Cap. (Caucasus). Of these species, only R. oblongus is sympatric with R. conicus in the latter’s native range (Zwölfer and Harris, 1984), and may indeed be a subspecies (Klein and Seitz, 1994).

A sixth species, R. inquilinus Gyll., described from Finland, appears to be a small individual of R. conicus (Zwölfer and Harris, 1984).

No other species of Rhinocyllus have been introduced as biological agents or are found outside Europe, North Africa and western Asia.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Containment/Zoning

The movement of R. conicus across USA state borders is now prohibited, an attempt by the authorities to contain the impact of this weevil on native thistles.

 

Gaps in Knowledge/Research Needs

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More work is needed to better understand the genetic patterns underlying ecotypic differences in R. conicus and to see if the different ecotypes show any degree of reproductive incompatibility.

References

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Alonso-Zarazaga MA, Talamelli F, 2011. Fauna Europaea. Fauna Europaea (online). http://www.faunaeur.org/full_results.php?id=248915

Andres LA, Rees NE, 1995. Musk thistle. Biological control in the western United States, 3361 [ed. by Niechols, J. R. \Andres, L. A. \BeardsleyJW, \Geoden, R. D. \Jackson, C. G.]. California, USA: University of California Division of Agriculture and Natural Resources, 248-251.

Arnett AE, Louda SM, 2002. Re-test of Rhinocyllus conicus host specificity, and the prediction of ecological risk in biological control. Biological Conservation, 106(2):251-257.

Boldt PE, Kok LT, 1982. Bibliography of Rhinocyllus conicus Froel. (Coleoptera: Curculionidae), an introduced weevil for the biological control of Carduus and Silybum thistles. Bulletin of the Entomological Society of America, 28(4):355-358.

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Cullen J, Sheppard AW, 2012. Carduus nutans L. - nodding thistle. In: Biological control of weeds in Australia 1960 to 2010 [ed. by Julien, M. \McFadyen, R. \Cullen, J.]. Melbourne, Australia: CSIRO Publishing, 118-130.

Denton J, 2011. Rhinocyllus conicus (Frölich) (Col.: Curculionidae) in Surrey and South Essex. British Journal of Entomology and Natural History, 24(4):204. http://www.benhs.org.uk

DePrenger-Levin ME, Grant TA III, Dawson C, 2010. Impacts of the introduced biocontrol agent, Rhinocyllus conicus (Coleoptera: Curculionidae), on the seed production and population dynamics of Cirsium ownbeyi (Asteraceae), a rare, native thistle. Biological Control, 55(2):79-84. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WBP-50KWFY0-1&_user=10&_coverDate=11%2F30%2F2010&_rdoc=2&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%236716%232010%23999449997%232353748%23FLA%23display%23Volume)&_cdi=6716&_sort=d&_docanchor=&_ct=11&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=78efe49241aa2b1324dbea78e84c1945&searchtype=a

Desrochers AM, Bain JF, Warwick SI, 1988. The biology of Canadian weeds. 89. Carduus nutans L. and Carduus acanthoides L. Canadian Journal of Plant Science, 68(4):1053-1068

Feldman SR, 1997. Biological control of plumeless thistle (Carduus acanthoides L.) in Argentina. Weed Science, 45(4):534-537.

Gassmann A, Kok L-T, 2002. Musk thistle (nodding thistle). In: Biological control of invasive plants in the eastern United States [ed. by Driesche, R. Van \Blossey, B. \Hoddle, M. \Lyon, S. \Reardon, R.]. Washington, DC, USA: USDA Forest Service, 229-245.

GBIF, 2012. Global Biodiversity Information Facility. Global Biodiversity Information Facility (GBIF). http://data.gbif.org

Goeden RD, 1995. Milk thistle. Biological control in the western United States, 3361 [ed. by Niechols, J. R. \Andres, L. A. \Beardsley, J. W. \Geoden, R. D. \Jackson, C. G.]. California, USA: University of California Division of Agriculture and Natural Resources, 245-247.

Goeden RD, Ricker DW, 1977. Establishment of Rhinocyllus conicus on milk thistle in southern California. Weed Science, 25(3):288-292.

Goeden RD, Ricker DW, 1978. Establishment of Rhinocyllus conicus (Col.: Curculionidae) on Italian thistle in southern California. Environmental Entomology, 7(6):787-789.

Goeden RD, Ricker DW, 1985. Seasonal asynchrony of Italian thistle, Carduus pycnocephalus, and the weevil, Rhinocyllus conicus (Coleoptera: Curculionidae), introduced for biological control in southern California. Environmental Entomology, 14(4):433-436.

Harris P, 1981. Carduus nutans L., nodding thistle and C. acanthoides L., plumeless thistle (Compositae). Biological control programmes against insects and weeds in Canada 1969-1980 [ed. by Kelleher, J.S.\Hulme, M.A.]. Slough, UK: Commonwealth Agricultural Bureaux, 115-126.

Harris P, Zwölfer H, 1971. Biological control of weeds in Canada, 1959-1968. 29. Carduus acanthoides L., welted thistle, and C. nutans L., nodding thistle (Compositae). Technical Communications. Commonwealth Institute of Biological Control, 4:76-9.

Hodgson JM, Rees NE, 1976. Dispersal of Rhinocyllus conicus for biocontrol of musk thistle. Weed Science, 24(1):59-62

Jessep CT, 1975. Introduction of a weevil for biological control of nodding thistle. In: Proceedings of the 28th New Zealand Weed and Pest Control Conference. 205-206.

Jessep CT, 1981. Nodding thistle receptacle weevil, Rhinocyllus conicus (Froelich), life cycle. DSIR Information Series, 105. 37.

Klein M, Seitz A, 1994. Geographic differentiation between populations of Rhinocyllus conicus Frölich (Coleoptera: Curculionidae): concordance of allozyme and morphometric analysis. Zoological Journal of the Linnean Society, 110(2):181-191.

Laing JE, Heels PR, 1978. Establishment of an introduced weevil Rhinocyllus (Col., Curculionidae) for the biological control of nodding thistle Carduus nutans (Compositae) in Southern Ontario. Proceedings of the Entomological Society of Ontario, 109:3-8.

Louda SM, 1998. Population growth of Rhinocyllus conicus (Coleoptera: Curculionidae) on two species of native thistles in Prairie. Environmental Entomology, 27(4):834-841.

Louda SM, Kendall D, Connor J, Simberloff D, 1997. Ecological effects of an insect introduced for the biological control of weeds. Science (Washington), 277(5329):1088-1090.

Louda SM, Potvin MA, 1995. Effect of inflorescence-feeding insects on the demography and lifetime fitness of a native plant. Ecology, 76(1):229-245.

Louda SM, Potvin MA, Collinge SK, 1990. Predispersal seed predation, postdispersal seed predation and competition in the recruitment of seedlings of a native thistle in Sandhills prairie. American Midland Naturalist, 124(1):105-113.

Maw MG, 1982. Effect of Rhinocyllus conicus on non-target thistles. Proceedings of a Biological bontrol of weeds workshop. In: Proceedings of a Biological control of weeds workshop (unpublished).

Micinski S, Cookson C, 2011. Range expansion of Rhinocyllus conicus Froelich on musk thistle into southwestern Arkansas. Southwestern Entomologist, 36(1):77-84. http://sswe.tamu.edu/

Page AR, Lacey KL, 2006. Carduus nutans (nodding thistle). Economic impact assessment of Australian weed biological control. Adelaide, Australia: CRC for Australian Weed Management, 59-60.

Rand TA, Louda SM, 2012. Exotic weevil invasion increases floral herbivore community density, function, and impact on a native plant. Oikos, 121(1):85-94. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-0706

Russell FL, Louda SM, Rand TA, Kachman SD, 2007. Variation in herbivore-mediated indirect effects of an invasive plant on a native plant. Ecology, 88(2):413-423. http://www.esajournals.org/perlserv/?request=get-abstract&doi=10.1890%2F0012-9658%282007%2988%5B413%3AVIHIEO%5D2.0.CO%3B2

Sagliocco JL, Kwong RM, Morley T, 2012. Cirsium vulgare (Savi) Tenore - spear thistle. In: Biological control of weeds in Australia 1960 to 2010 [ed. by Julien, M. \McFadyen, R. \Cullen, J.]. Melbourne, Australia: CSIRO Publishing, 184-189.

Sauer SA, Bradley KL, 2008. First record for the biological control agent Rhinocyllus conicus (Coleoptera: Curculionidae) in a threatened native thistle, Cirsium hillii (Asteraceae), in Wisconsin, U.S.A. Entomological News, 119(1):90-95. http://www.bioone.org/perlserv/?request=get-current-issue

Sheppard AW, Aeschlimann JP, Sagliocco JL, Vitou J, 1991. Natural enemies and population stability of the winter-annual Carduus pycnocephalus L. in Mediterranean Europe. Acta Oecologica, 12(6):707-726.

Sheppard AW, Cullen JM, Aeschlimann JP, 1994. Predispersal seed predation on Carduus nutans (Asteraceae) in southern Europe. Acta Oecologica, 15(5):529-541.

Turner CE, Pemberton RW, Rosenthal SS, 1987. Host utilization of native Cirsium thistles (Asteraceae) by the introduced weevil Rhinocyllus conicus (Coleoptera: Curculionidae) in California. Environmental Entomology, 16(1):111-115

Unruh TR, Goeden RD, 1987. Electrophoresis helps to indentify which race of the introduced weevil, Rhinocyllus conicus (Coleoptera: Curculionidae), has transferred to two native southern California thistles. Environmental Entomology, 16:979-983.

US Fish and Wildlife Service, 2010. In: Pitcher's thistle (Cirsium pitcheri). 5-Year Review: Summary and Evaluation. US Fish and Wildlife Service, 29 pp.. http://ecos.fws.gov/docs/five_year_review/doc3083.pdf

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Wiggins GJ, Grant JF, Lambdin PL, Ranney JW, Wilkerson JB, Reed A, Follum RA, 2010. Host utilization of field-caged native and introduced thistle species by Rhinocyllus conicus. Environmental Entomology, 39(6):1858-1865. http://docserver.ingentaconnect.com/deliver/connect/esa/0046225x/v39n6/s20.pdf?expires=1297915494&id=0000&titleid=10265&checksum=C82D50039445B003B3FF015662BE54CC

Wilson RC, Andres LA, 1986. Larval and pupal parasites of Rhinocyllus conicus (Coleoptera: Curculionidae) in Carduus nutans in northern California. Pan-Pacific Entomologist, 62(4):329-332.

Woodburn TL, 1996. Interspecific competition between Rhinocyllus conicus and Urophora solstitialis, two biocontrol agents released in Australia against Carduus nutans. In: Proceedings of the 9th international symposium on biological control of weeds, Stellenbosch, South Africa, 19-26 January 1996 [ed. by Moran, V. C.\Hoffmann, J. H.]. Rondebosch, South Africa: University of Cape Town, 409-415.

Woodburn TL, Cullen JM, 1993. Effectiveness of Rhinocyllus conicus as a biological control agent for nodding thistle, Carduus nutans, in Australia. In: Proceedings I of the 10th Australian Weeds Conference and 14th Asian Pacific Weed Science Society Conference, Brisbane, Australia, 6-10 September, 1993 [ed. by Wilson, B. J.\Swarbrick, J. T.]. Queensland, Australia: Queensland Weed Society, 99-103.

Woodburn TL, Cullen JM, 1995. Release and establishment of the thistle-head weevil, Rhinocyllus conicus, in Australia. In: Proceedings of the Eighth International Symposium on Biological Control of Weeds [ed. by Delfosse, E. S. \Scott, R. R.]. Melbourne, Australia: DSIR/CSIRO, 411-414.

Zwölfer H, Harris P, 1984. Biology and host specificity of Rhinocyllus conicus (Froel.) (Col., Curculionidae), a successful agent for biocontrol of the thistle, Carduus nutans L. Zeitschrift für Angewandte Entomologie, 97(1):36-62.

Links to Websites

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WebsiteURLComment
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.
Plants USDAhttp://plants.usda.gov/java/nameSearch?keywordquery=Carduus+nutans&mode=sciname

Contributors

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26/03/12 Original text by:

A Sheppard, CSIRO Entomology, Australia

Distribution Maps

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