Biological control of cat’s claw creeper, Macfadyena unguis-cati . unguis-cati...Biological...
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Biological control of cats claw creeper, Macfadyena unguis-cati (L.) A.H.Gentry(Bignoniaceae), in South Africa
A.M. King*, H.E. Williams & L.G. MadireAgricultural Research Council-Plant Protection Research Institute, Private Bag X134, Queenswood, 0121 South Africa
The exotic vine Macfadyena unguis-cati (L.) A.H.Gentry (Bignoniaceae), cats claw creeper, hasbecome a significant threat to the biodiversity of a variety of sensitive ecosystems in SouthAfrica. Owing to the nature of the infestations, as well as the difficulties and prohibitive costsassociated with both mechanical and chemical controls, biological control is considered to bethe most practical and sustainable means of successfully managing the weed in South Africa.The biological control programme against M. unguis-cati was initiated in 1996 and resulted inthe release of Charidotis auroguttata Boheman (Coleoptera: Chrysomelidae: Cassidinae).Despite repeated releases, initial rates of establishment were low. Where successfully estab-lished, populations of the beetle have been slow to build-up, leading to only limited impacton the weed. Prompted by this lack of success, as well as the high potential for further spreadof the weed, additional natural enemies were sought. Two lace bugs, Carvalhotingis visendaDrake & Hambleton, and Carvalhotingis hollandi Drake (Hemiptera: Tingidae), a leaf-miningbeetle Hylaeogena (Hedwigiella) jureceki Obenberger (Coleoptera: Buprestidae), a leaf-tyingmoth Hypocosmia pyrochroma Jones (Lepidoptera: Pyralidae) and a seed-feeding weevilApteromechus notatus (Hustache) (Coleoptera: Curculionidae) were subsequently importedinto quarantine in South Africa for host-specificity testing. With the exception of A. notatus,all have been approved for release and are exhibiting promising initial rates of establishmentand damage at a number of field localities. Impact studies have shown that cats claw creeperis susceptible to sustained herbivore pressure.
Key words: biological weed control, insect natural enemies, foliar feeding, agent efficacy,climatic effects, management.
The exotic perennial vine, Macfadyena unguis-cati(L.) A.H.Gentry (Bignoniaceae) (Fig. 1), alsoknown as cats claw creeper, is a significant threatto biodiversity in a number of regions of SouthAfrica. Originally a native of Central and tropicalSouth America, including the West Indies, the vinehas become naturalized on every continent exceptAntarctica (Starr & Starr 2008). This extensiverange has been facilitated through the horticul-tural trade which distributed the plant as an orna-mental (Sparks 1999; Downey & Turnbull 2007;Starr & Starr 2008). Showy yellow flowers coupledwith its climbing habit make the fast-growingcreeper ideal to screen-off walls or unsightly build-ings. The plant has become invasive in a number ofcountries including South Africa, Australia, China,the Cook Islands, India, Mauritius, New Caledonia,New Zealand, Runion, Saint Helena, Vanuatuand the U.S.A., including Hawaii (Starr & Starr 2008).
Within South Africa, M. unguis-cati is still
considered to be in the early stages of invasionand although it is spreading, the current range islimited relative to its potential distribution aspredicted by its climatic requirements (Rafter et al.2008). Nevertheless, the weed has formed a numberof very dense infestations and has become prob-lematic in the Gauteng, Limpopo, Mpumalangaand North West provinces, and in some areas ofthe KwaZulu-Natal Province (Fig. 2). Using theclimate comparison program CLIMEX, Rafter et al.(2008) constructed a model which predicted catsclaw creeper to be best suited to the climate overmuch of South Africas southern and easterncoastline between latitudes 26S and 33S, andprobably excluded from natural systems in thecentral and western regions of the country by bothcold and dry stress. The model also predictedthat the subtropical and tropical coastal areas ofnorthern KwaZulu-Natal, a region as yet free ofM. unguis-cati infestation, would be highly suitablefor invasion.
Macfadyena unguis-cati is a woody, frost-tolerant,*To whom correspondence should be addressed.E-mail: email@example.com
African Entomology 19(2): 366377 (2011)
structural parasite normally found associated withforest and riparian habitats (Raghu et al. 2006). Itsdistinctive leaves consist of two leaflets and a ter-minal three-forked tendril from which the vinedraws its name. A tiny hardened hook on eachfork can attach to most surfaces and thus enablethe plant to climb up walls, tree trunks and overother vegetation (Sparks 1999). This climbing habitenables the plant to form dense infestations in thecanopy of trees where branches, and eventuallyentire trees, can be killed through a combination ofboth shading and weight (Downey & Turnbull2007). In the absence of climbing support, stemsreadily grow along the ground and are capable of
forming a dense groundcover which precludesthe growth and seed germination of indigenousunderstorey vegetation (Williams 2002; Downey& Turnbull 2007). In areas of introductionM. unguis-cati has become a significant invader ofcultivated orchards and plantations, ripariancorridors, natural forest remnants and disturbedareas such as roadsides and abandoned urbanspaces (Williams 2002).
The management of cats claw creeper is extremelydifficult and little success has been achieved witheither chemical or mechanical control in SouthAfrica (Williams et al. 2008). Control is hamperedby the weeds extensive and vigorous growth,
King et al.: Biological control of cats claw creeper (Bignoniaceae) 367
Fig. 1. Macfadyena unguis-cati. (Drawn by M. Steyn, first published in Henderson (1995), ARC-Plant ProtectionResearch Institute, Pretoria.)
X 1X 1
profuse seed production and the presence of anetwork of underground root tubers. Macfadyenaunguis-cati produces numerous flattened pod-likefruits, or capsules, each containing on average90 winged seeds. Membranous wings on the seedsaid spread, which is predominantly facilitated bywind or water, making them well suited to dispersaldown riparian corridors (Vivian-Smith & Panetta2004; Downey & Turnbull 2007). Although seedproduction is high, Vivian-Smith & Panetta (2004)suggest that cats claw creeper does not have apersistent seed bank. Seed longevity and seedbank densities were found to be low relative tosimilar invasive vines. However, the presence oftubers makes infestations extremely resilient asthey readily re-sprout if aerial parts of the plantare damaged or removed, for example throughmechanical removal or fire. Stems growing alongthe ground are also capable of producing rootsand tubers at leaf nodes which form new plants ifseparated from the parent plant. This ability enables
the plant to withstand adverse conditions such asheavy frost and drought (King & Dhileepan 2009).Whilst spread is facilitated by seeds, the mechanismof persistence is predominantly through the tuberbank (Vivian-Smith & Panetta 2004; Osunkoyaet al. 2009).
Any management strategy must therefore pri-marily target the tuber bank but also endeavourto remove mature vines in order to limit seedproduction and further spread (Vivian-Smith &Panetta 2004). Chemical control options are thuslargely unsuccessful as they predominantly targetabove-ground growth and have little perceivableimpact on the tuber bank. The use of chemicalapplications is further complicated by the risk ofnon-target effects. Broad-leaf herbicides can onlybe used selectively due to the propensity of catsclaw creeper to invade ecologically sensitive oreconomically important ecosystems (Sparks 1999;Dhileepan et al. 2005). Whilst some success hasbeen achieved with mechanical and chemical
368 African Entomology Vol. 19, No. 2, 2011
Fig. 2.Distribution of Macfadyena unguis-cati in South Africa. (Drawn by L.Henderson;data source:SAPIA database,ARC-Plant Protection Research Institute, Pretoria.)
control (Downey & Turnbull 2007), becauserepeated follow-up is required, these techniquescan only be used cost-effectively at very smallscales. Weed management practitioners have thusprioritised biological control as the only practicaland long-term solution to cats claw creeper infes-tations. In this paper we review the current statusof the biological control programme against M.unguis-cati in South Africa, in particular (i) thebiology and host specificity of the six candidatenatural enemies, (ii) the distribution and efficacyof these agents, and (iii) attempt to consolidatethe work done since 1999 that has not yet beenpublished.
THE BIOLOGICAL CONTROL AGENTS
Charidotis auroguttata Boheman(Coleoptera: Chrysomelidae: Cassidinae)
The biological control programme against M.unguis-cati in South Africa was initiated in 1996by the Agricultural Research Councils Plant Pro-tection Research Institute when nine potentialagents were collected during surveys for naturalenemies of other weeds of South American origin(Sparks 1999). Of the candidates collected, thegolden-spotted tortoise beetle C. auroguttata wasprioritised for introduction and screening owingto the narrow host ranges and specialized feedinghabits normally attributed to the Cassidinae(Jolivet 1988). Under laboratory conditions C. auro-guttata displayed a high rate of populationincrease which enabled the completion of severalgenerations per year. It also exhibited good adultlongevity and fecundity, and demonstrated highrates of both adult and larval feeding whichresulted in considerable leaf skeletonization(Williams 2002). Permission for its release in SouthAfrica was granted in 1999 and C. auroguttatabecame the first biological control agent releasedagainst cats claw creeper anywhere in the world(Sparks 1999). Confronted with similar problemsassociated with M. unguis-cati infe