Biological control of Paterson's curse with crown and root boring weevils
Note Number: LC0144
Published: October 2001
This Landcare Note describes the Paterson's curse crown and root boring weevils, Mogulones spp., and their use in biological control of Echium plantagineum.
Common and scientific names
Paterson's curse crown weevil, Paterson's curse crown-boring weevil
Mogulones larvatus (Schultze)
Paterson's curse root weevil, Paterson's curse root-boring weevil
Mogulones geographicus (Goeze)
Family: Curculionidae (weevils)
Paterson's curse, Echium plantagineum, is a noxious weed of European origin that now occurs in most states of Australia and is mainly a problem in pastures, on roadsides and in degraded and disturbed areas. It reduces agricultural productivity by competing with more nutritious pasture plants and because it is toxic to livestock when ingested continuously.
The national program on biological control of Paterson's curse is a cooperative effort involving the CRC for Weed Management Systems, CSIRO Division of Entomology, NRE and government authorities in other States.
In the first phase of the program the natural enemies of Paterson's curse were studied in Europe and potential biological control agents were imported to Australia for thorough testing under quarantine conditions.
In the second phase, cultures of insects shown to be specific to Paterson's curse were supplied to the States for rearing and release throughout the weed's distribution. Release sites are established with the cooperation of community groups and farmers to enable future collection and redistribution of the insects. Redistribution from release sites and evaluation of the effects of these insects on the weed population is the third phase of the national program.
The crown boring weevil and the root boring weevil are two European insects that have been released in Australia for the biological control of Paterson's curse.
Adults - The crown boring weevil (Figures 1 and 8) is 3.5 to 4 mm long. It is dark brown and white with a characteristic pattern. The root boring weevil (Figures 2 and 8) is slightly larger, 4 to 5 mm long, and has a light brown body covered with fine, pale lines. Both beetles have very hard bodies, a long snout (the rostrum), with mouthparts located at the tip, and elbowed, club-shaped antennae that can be folded against the snout.
Eggs - M. larvatus eggs are 0.7mm long x 0.4mm wide, oval in shape and yellow. M. geographicus eggs are 0.75mm long x 0.25mm wide, oval and white in colour. They are laid into the leaf stalks of Paterson's curse rosettes. Crown weevil females produce 450 eggs on average, while root weevils produce an average of 250 eggs.
Larvae - up to 6mm long, C-shaped, legless, cream or white in colour with a brown head; found inside the root or the crown of the plant. Larvae have three growth stages (instars).
Pupae - about 4 mm long, found in earthen cells in the soil close to the host plant.
The weevils have one generation per year. Adult crown weevils start feeding and egg laying between February and April after Paterson's curse rosettes have established. Root weevils become active between March and June. Egg laying can continue through winter until October (root weevil) or November (crown weevil). Eggs are laid in leaf stalks, mostly near the crown. Larvae hatch from the eggs after about 1 week and initially feed within the leaf stalk. As they grow they move downwards to mine the crown (M. larvatus), or root (M. geographicus) during autumn and early winter.
After feeding is completed in spring, the mature larvae of both species move out of the plant into the soil and form earthen cells in which they pupate. Adults emerge later in spring or early summer, then disperse and feed for several weeks on Paterson's curse flowers and foliage, before resting in a dormant state (aestivating) over summer in the leaf litter or soil. Feeding resumes after rains in autumn and is followed shortly afterwards by mating and egg laying.
Larvae damage the crown and root making plants less competitive and reducing their ability to produce seeds. Adults chew holes in leaf blades causing "shot hole" damage (Figure 5) and also feed on leaf stalks. The plant may form calluses where the stalks have been attacked (Figure 6). In plants heavily infested with M. larvatus, damage by young larvae is seen as dark lines in leaf stalks, and late larval damage is evident as a black discharge from the crowns (Figure 7). M. geographicus larvae mine within the taproot.
The survival and impact of the crown weevil is limited by livestock grazing, especially in autumn. The stock eat the eggs and young larvae along with the plant material they consume.
The crown weevil has been released at over 1000 sites in Australia since 1994 and has been redistributed from 1996 onwards. The root boring weevil was first released in early 1996. It has proved to be much harder to rear, so few releases have been made.
Releases are made with 300 to 500 or more adult M. larvatus and M. geographicus adults in autumn at sites with dense populations of Paterson's curse rosettes.
Release sites should be managed to maximise the chances of insect establishment. Since the survival of the crown weevil is limited by grazing and enhanced by growth of Paterson's curse rosettes in early autumn, the most successful release sites are those without livestock and where rosettes establish early. Release sites can be fenced to exclude stock and irrigated to promote rosette growth. Sites should not be cultivated and no herbicides or insecticides should be used in or around them.
Release site management can include grazing in late summer to reduce grass cover and promote germination of the weed. The weevils are inactive in the soil during this period. Irrigation of sites in early autumn to promote rosette growth in years when the autumn break is late will help ensure survival of the crown weevil.
Adult weevils can be harvested for redistribution from established sites. In late spring, beat or shake weevils from flowering Paterson's curse onto a hand-held tray. In autumn, weevils can be collected from rosettes with "shot holed" leaves. Autumn releases are generally more successful than spring releases. This effect can be compensated for by releasing larger numbers of weevils in spring.
Other natural enemies of Paterson's curse
Four other species of insect which attack Paterson's curse have been released in Victoria. The leaf mining moth, Dialectica scalariella, was first released in 1988 and was well established by 1992. The larvae mine beneath the cuticle of the leaves and can cause premature leaf death. Serious damage only occurs in areas with summer rainfall and the moth contributes little to overall control. The taproot flea beetle, Longitarsus echii, was first released in late 1996 and has established at several sites. Internal damage to the taproot caused by the feeding of mature larvae is the most important impact of this agent.
The stem-boring beetle, Phytoecia coerulescens, was first released in December 1998. The larvae mine in the stems and may completely eat them out, but have lesser effect on large, thick-stemmed plants. The flower feeding beetle, Meligethes planiusculus, was also first released in 1998. Adults and larvae feed on the flowers and developing seed and reduce the production of seed.
Biological control cannot totally eradicate a weed but can reduce the spread and density of infestations. In some cases control is achieved to the level where the weed is no longer of concern and no other control is necessary. More commonly, other methods are still required to achieve the desired level of control.
Biological control should not be considered the complete answer to a Paterson's curse problem. It should be used in conjunction with other control measures in an integrated management plan. Consult The Paterson's Curse Management Handbook for detailed information on integrated management of Paterson's curse.
Consult NREs Landcare Notes, available on the NRE web site or from a Catchment Management Officer in your region.
LC0173: Paterson's curse
LC0155: Biological control of Paterson's curse with the taproot flea beetle
LC0159: Biological control of Paterson's curse with the stem-boring beetle, and
LC0165: Biological control of Paterson's curse with the flower feeding beetle
For further information on the biological control of Paterson's curse contact Agriculture Victoria - Frankston, Keith Turnbull Research Institute:
Ph: (03) 9785 0111
Fax: (03) 9785 2007
Morley, T. and Stapleton, P. (1999) The Paterson's Curse Management Handbook. Department of Natural Resources and Environment.
Shepherd, A.W., Smyth, M. and Swirepik, A. (1999) Impact of the root-crown weevil (Mogulones larvatus) and other biocontrol agents on Paterson's curse in Australia: an update. Pp. 343-346 in A.C.Bishop, M.Boersma and C.D.Barnes (Eds.) 12th Australian Weeds Conference Papers and Proceedings. Devonport, Tasmanian Weed Society.
Vayssieres, J.F. and Wapshere, A.J. (1983) Life-histories and host specificities of Ceutorhynchus geographicus (Goeze) and C. larvatus Schultze (Coleoptera: Curculionidae), potential biological control agents for Echium. Bulletin of Entomological Research 73, 431-440.
Drafted by Sue Darby, July 1994. Revised and updated by Ian Faithfull and Tom Morley September 2000. Keith Turnbull Research Institute, Frankston. Photographs by CSIRO Division of Entomology (Figures 1 and 2) and Tom Morley (Figures 3 to 8).
The national program on biological control of Paterson's curse has been funded by NRE, CSIRO Division of Entomology, NSW Agriculture, Primary Industries South Australia, Agriculture Western Australia, The Woolmark Company, Meat and Livestock Australia and the Cooperative Research Centre for Weed Management Systems (Weeds CRC). Distribution of Paterson's curse agents is a project of the Weeds CRC.
This note replaces note number BC0010