October 2001 Biological control of Paterson's curse LC0144 with crown and root boring weevils ISSN 1329-833X Keith Turnbull Research Institute, Frankston This Landcare Note describes the Paterson’s curse crown Description and root boring weevils, Mogulones spp., and their use in Adults - The crown boring weevil (Figures 1 and 8) is 3.5 biological control of Echium plantagineum. to 4 mm long. It is dark brown and white with a characteristic pattern. The root boring weevil (Figures 2 Common and scientific names and 8) is slightly larger, 4 to 5 mm long, and has a light Paterson’s curse crown weevil, Paterson’s curse crown- brown body covered with fine, pale lines. Both beetles boring weevil have very hard bodies, a long snout (the rostrum), with Mogulones larvatus (Schultze) mouthparts located at the tip, and elbowed, club-shaped antennae that can be folded against the snout. Paterson’s curse root weevil, Paterson’s curse root-boring weevil Mogulones geographicus (Goeze) Family: Curculionidae (weevils) Background 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, Figure 1. Adult crown weevil. 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 Figure 2. Adult root weevil. two European insects that have been released in Australia for the biological control of Paterson's curse. Eggs - M. larvatus eggs are 0.7mm long x 0.4mm wide, oval in shape and yellow. M. geographicus eggs are © State of Victoria, Department of Natural Resources and Environment 2002 Page 1 Biological control of ragwort with the ragwort plume moth LC0144 0.75mm long x 0.25mm wide, oval and white in colour. the soil and form earthen cells in which they pupate. They are laid into the leaf stalks of Paterson’s curse Adults emerge later in spring or early summer, then rosettes. Crown weevil females produce 450 eggs on disperse and feed for several weeks on Paterson’s curse average, while root weevils produce an average of 250 flowers and foliage, before resting in a dormant state eggs. (aestivating) over summer in the leaf litter or soil. Feeding Larvae - up to 6mm long, C-shaped, legless, cream or resumes after rains in autumn and is followed shortly white in colour with a brown head; found inside the root or afterwards by mating and egg laying. 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. Figure 5. Shot-holes in leaf blades caused by adult weevils. Figure 3. Eggs are laid into the leaf stalks. Figure 6. Calluses on leaf stalks are caused by adult feeding. Figure 4. Larvae of the root weevil damage the taproot. Life cycle 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 Figure 7. Black discharge indicates damage to the crown caused by larvae of the crown weevil. © State of Victoria, Department of Natural Resources and Environment 2002 Page 2 Biological control of ragwort with the ragwort plume moth LC0144 Impact Adult weevils can be harvested for redistribution from established sites. In late spring, beat or shake weevils from Larvae damage the crown and root making plants less flowering Paterson's curse onto a hand-held tray. In competitive and reducing their ability to produce seeds. autumn, weevils can be collected from rosettes with "shot Adults chew holes in leaf blades causing "shot hole" holed" leaves. Autumn releases are generally more damage (Figure 5) and also feed on leaf stalks. The plant successful than spring releases. This effect can be may form calluses where the stalks have been attacked compensated for by releasing larger numbers of weevils in (Figure 6). In plants heavily infested with M. larvatus, spring. damage by young larvae is seen as dark lines in leaf stalks, and late larval damage is evident as a black discharge from Other natural enemies of Paterson's the crowns (Figure 7). M. geographicus larvae mine within the taproot. curse The survival and impact of the crown weevil is limited by Four other species of insect which attack Paterson’s curse livestock grazing, especially in autumn. The stock eat the have been released in Victoria. The leaf mining moth, eggs and young larvae along with the plant material they Dialectica scalariella, was first released in 1988 and was consume. 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. Integrated management Biological control cannot totally eradicate a weed but can Figure 8. Paterson’s curse root weevil (left) and crown weevil (right). reduce the spread and density of infestations. In some cases control is achieved to the level where the weed is no Releases longer of concern and no other control is necessary. More commonly, other methods are still required to achieve the The crown weevil has been released at over 1000 sites in desired level of control. Australia since 1994 and has been redistributed from 1996 onwards. The root boring weevil was first released in early Biological control should not be considered the complete 1996. It has proved to be much harder to rear, so few answer to a Paterson’s curse problem. It should be used in releases have been made. conjunction with other control measures in an integrated management plan. Releases are made with 300 to 500 or more adult M. larvatus and M. geographicus adults in autumn at sites Consult The Paterson’s Curse Management Handbook for with dense populations of Paterson’s curse rosettes. detailed information on integrated management of Paterson’s curse. Release sites should be managed to maximise the chances of insect establishment. Since the survival of the crown Further information weevil is limited by grazing and enhanced by growth of Paterson's curse rosettes in early autumn, the most Consult NREs Landcare Notes, available on the NRE web successful release sites are those without livestock and site or from a Catchment Management Officer in your where rosettes establish early. Release sites can be fenced region. to exclude stock and irrigated to promote rosette growth. LC0173: Paterson’s curse Sites should not be cultivated and no herbicides or LC0155: Biological control of Paterson’s curse with the insecticides should be used in or around them. taproot flea beetle Release site management can include grazing in late LC0159: Biological control of Paterson’s curse with the summer to reduce grass cover and promote germination of stem-boring beetle, and the weed. The weevils are inactive in the soil during this LC0165: Biological control of Paterson’s curse with the period. Irrigation of sites in early autumn to promote flower feeding beetle rosette growth in years when the autumn break is late will help ensure survival of the crown weevil. © State of Victoria, Department of Natural Resources and Environment 2002 Page 3 Biological control of ragwort with the ragwort plume moth LC0144 For further information on the biological control of Acknowledgments Paterson’s curse contact Agriculture Victoria - Frankston, Drafted by Sue Darby, July 1994. Revised and updated by Keith Turnbull Research Institute: Ian Faithfull and Tom Morley September 2000. Ph: (03) 9785 0111 Photographs by CSIRO Division of Entomology (Figures Fax: (03) 9785 2007 1 and 2) and Tom Morley (Figures 3 to 8).