A Biological Control Feasibility Study of the Invasive Weed-Air Potato, Dioscorea bulbifera L. (Dioscoreaceae): an Effort to Increase Biological Control Transparency and Safety Author(s): G. S. Wheeler, R. W. Pemberton, L. Raz Source: Natural Areas Journal, 27(3):269-279. Published By: Natural Areas Association DOI: http://dx.doi.org/10.3375/0885-8608(2007)27[269:ABCFSO]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.3375/0885-8608%282007%2927%5B269%3AABCFSO %5D2.0.CO%3B2 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. CONSERVATION ISSUES • A Biological Control Feasibility Study of the Invasive Weed-Air Potato, Dioscorea bulbifera L. (Dioscoreaceae): an Effort to Increase Biological Control Transparency and Safety G.S. Wheeler1 R.W. Pemberton USDA฀Agricultural฀Research฀Service Invasive฀Plant฀Research฀Lab 3225฀College฀Ave. Ft฀Lauderdale,฀FL฀33314 L. Raz Fairchild฀Tropical฀Botanic฀Garden Center฀for฀Tropical฀Plant฀Conservation Coral฀Gables,฀FL฀33156-4242 • 1฀฀Corresponding฀author:฀ wheelerg@saa.ars.usda.gov;฀954-475-6546 Natural฀Areas฀Journal฀26:269–279 Volume 27 (3), 2007 ABSTRACT:฀Biological฀control฀is฀increasingly฀used฀against฀invasive฀weeds฀of฀natural฀areas.฀Scientific฀ and฀regulatory฀review฀of฀safety-related฀research฀occurs฀before฀candidate฀biological฀control฀agents฀can฀ be฀released.฀To฀increase฀safety,฀efficacy,฀and฀transparency฀of฀the฀process,฀we฀suggest฀that,฀prior฀to฀establishing฀a฀project,฀a฀feasibility฀study฀be฀conducted฀on฀a฀potential฀target฀for฀biological฀control฀to฀judge฀ whether฀the฀project฀is฀appropriate.฀The฀present฀paper฀is฀both฀a฀feasibility฀study฀of฀an฀important฀invasive฀ weed฀and฀a฀guide฀to฀doing฀biological฀control฀feasibility฀studies฀on฀other฀weed฀pests.฀The฀invasive฀weed฀ Dioscorea฀bulbifera฀L.฀threatens฀the฀biodiversity฀of฀many฀natural฀areas฀in฀the฀southeastern฀United฀States.฀ Current฀control฀efforts฀directed฀against฀this฀invasive฀species฀include฀herbicidal฀or฀manual฀removal,฀both฀ of฀which฀are฀costly฀and฀ineffective.฀Biological฀control฀using฀insects฀that฀selectively฀feed฀on฀this฀species฀ while฀leaving฀desirable฀native฀and฀economic฀species฀unharmed฀may฀be฀a฀useful฀option.฀As฀herbivore฀ host฀range฀may฀be฀limited฀by฀taxonomic฀affinities฀and฀the฀lack฀of฀sympatry฀with฀potential฀host฀species,฀ we฀propose฀that฀this฀weed฀will฀be฀a฀relatively฀safe฀target฀because฀of฀taxonomic฀and฀geographic฀isolation฀ from฀desirable฀native฀and฀economic฀plant฀species.฀The฀family฀Dioscoreaceae฀is฀poorly฀represented฀in฀ North฀America,฀north฀of฀Mexico,฀and฀the฀two฀native฀species฀that฀are฀sympatric฀with฀the฀weed฀are฀from฀ a฀different฀subgeneric฀taxon฀than฀the฀weed.฀The฀West฀Indian฀and฀northern฀Mexican฀species,฀while฀more฀ diverse,฀are฀also฀assigned฀to฀different฀subgeneric฀taxa,฀and฀are฀geographically฀isolated฀from฀the฀northern฀ range฀of฀the฀weed.฀Initial฀searches฀for฀biological฀control฀agents฀have฀begun฀and฀will฀continue฀within฀ its฀large฀transcontinental฀native฀range.฀However,฀further฀research฀is฀needed฀that฀will฀better฀delimit฀the฀ geographic฀origin฀of฀the฀weed’s฀North฀American฀population฀within฀its฀large฀native฀range.฀This฀will฀aid฀ in฀the฀detection฀of฀suitable฀natural฀enemies.฀Much฀of฀the฀information฀we฀acquired฀and฀analyzed฀in฀this฀ feasibility฀ study฀ is฀ required฀ for฀ the฀ environmental฀ assessment฀ normally฀ submitted฀ for฀ approval฀ prior฀ to฀ the฀ introduction฀ of฀ a฀ biological฀ control฀ agent.฀We฀ suggest฀ that฀ this฀ type฀ of฀ analysis฀ will฀ be฀ better฀ considered฀at฀the฀beginning฀of฀the฀process.฀If฀this฀type฀of฀analysis฀is฀done฀prior฀to฀or฀at฀the฀beginning฀ of฀projects,฀potential฀conflicts฀and฀risks฀can฀be฀judged฀and฀then฀better฀addressed฀during฀the฀projects฀to฀ ultimately฀produce฀safer,฀more฀acceptable฀agents฀for฀biological฀control. Index฀terms:฀air฀potato,฀air฀yam,฀biological฀control฀of฀weeds,฀Dioscorea฀bulbifera,฀feasibility฀study INTRODUCTION The฀safety฀of฀biological฀control฀has฀been฀ the฀ subject฀ of฀ recent฀ debate฀ and฀ discussion฀ (Follett฀ and฀ Duan฀ 2000;฀ Strong฀ and฀ Pemberton฀2000;฀Louda฀et.฀al.฀2003;฀and฀ others).฀ Safety฀ to฀ non-target฀ economic฀ plants฀has฀been฀a฀paramount฀concern฀since฀ the฀inception฀of฀biological฀control฀of฀weeds฀ (Dodd฀1940),฀but฀the฀potential฀use฀of฀native฀plants฀by฀biological฀control฀agents฀is฀a฀ relatively฀recent฀consideration.฀Increasing฀ evidence฀of฀the฀adoption฀of฀native฀plants฀ by฀ insects฀ introduced฀ for฀ biological฀ control฀of฀weeds฀began฀to฀emerge฀during฀the฀ 1980s฀ (Andres฀ 1981;฀Turner฀ et฀ al฀ 1987).฀ When฀ Cactoblastis฀ cactorum฀ (Bergoth)฀ (Lepidoptera:฀ Pyralidae)฀ was฀ discovered฀ in฀ Florida฀ in฀ 1989,฀ Habeck฀ and฀ Bennett฀ (1990)฀ and฀ Louda฀ et฀ al.฀ (1997)฀ reported฀ that฀ Rhinocyllus฀ conicus฀ (Froel.)฀ (Coleoptera:฀Curculionidae)฀was฀causing฀harm฀ to฀native฀North฀American฀Cirsium฀thistles,฀ and฀ the฀ issue฀ came฀ to฀ the฀ attention฀ of฀ ecologists฀and฀the฀media.฀A฀review฀of฀the฀ native฀plants฀used฀as฀developmental฀hosts฀ by฀biological฀control฀agents฀introduced฀to฀ the฀ United฀ States฀ found฀ that฀ virtually฀ all฀ of฀the฀plants฀used฀were฀closely฀related฀to฀ the฀target฀weed฀(Pemberton฀2000).฀In฀addition,฀all฀of฀the฀cases฀involved฀biological฀ control฀introductions฀made฀prior฀to฀1974,฀ when฀ the฀ potential฀ use฀ of฀ native฀ plants฀ began฀ to฀ be฀ considered฀ more฀ carefully.฀ This฀ increased฀ attention฀ to฀ native฀ plants฀ by฀biological฀control฀programs฀in฀the฀U.S.฀ mirrored฀ the฀ increased฀ interest฀ in฀ native฀ plants,฀ as฀ demonstrated฀ by฀ legislation฀ to฀ protect฀ rare฀ plants฀ and฀ the฀ growth฀ in฀ native฀plant฀societies฀(Pemberton฀2004).฀The฀ adoption฀ of฀ native฀ plants฀ by฀ biological฀ control฀ agents฀ introduced฀ in฀ earlier฀ eras฀ continues฀and฀increases฀in฀some฀cases,฀as฀ with฀C.฀cactorum฀on฀North฀American฀(and฀ potentially฀ Mexican)฀ prickly฀ pear฀ cacti฀ Opuntia฀(Johnson฀and฀Stiling฀1996).฀This฀ gives฀the฀impression฀that฀current฀biological฀ control฀of฀weeds฀practice฀is฀not฀as฀safe฀as฀ it฀ actually฀ is.฀ Remedies฀ to฀ this฀ problem฀ include฀ increased฀ transparency฀ of฀ practice฀and฀continued฀efforts฀to฀improve฀the฀ ecologically฀safe฀practice.฀One฀method฀to฀ achieve฀ both฀ is฀ to฀ conduct฀ and฀ publish฀ a฀ biological฀control฀feasibility฀study฀on฀the฀ prospective฀target฀weed. The฀ feasibility฀ study฀ can฀ be฀ a฀ decisionmaking฀process฀(i.e.,฀whether฀or฀not฀bioNatural Areas Journal 269 logical฀control฀should฀be฀pursued)฀or฀as฀a฀ process฀ to฀ adequately฀ address฀ ecological฀ safety฀of฀an฀intended฀program.฀The฀study฀ can฀also฀be฀a฀vehicle฀to฀develop฀political฀ and฀economic฀support฀for฀a฀program.฀Such฀ a฀study฀should,฀in฀our฀opinion,฀gather฀and฀ evaluate฀ information฀ on฀ the฀ following฀ topics,฀ all฀ of฀ which฀ are฀ discussed฀ in฀ this฀ example:฀ (1)฀ nature฀ of฀ damage฀ caused฀ by฀ the฀ weed,฀ (2)฀ ecological฀ damage,฀ (3)฀ economic฀damage,฀(4)฀area฀of฀origin฀and฀ geographic฀ distribution฀ of฀ the฀ weed,฀ (5)฀ identification,฀(6)฀taxonomy฀and฀analysis฀ of฀ related฀ plants฀ using฀ traditional฀ and฀ molecular฀ data,฀ (7)฀ Conflicts฀ of฀ interests฀ (e.g.,฀economically฀important฀species),฀(8)฀ potential฀risks฀of฀biological฀control฀to฀native฀plants,฀(9)฀secondary฀plant฀chemistry฀ and฀ its฀ potential฀ relevance฀ to฀ herbivory,฀ (10)฀level฀of฀specificity฀needed฀to฀avoid฀or฀ limit฀non-target฀effects฀and฀recommended฀ species฀ to฀ be฀ tested,฀ (11)฀ areas฀ surveyed฀ for฀natural฀enemies,฀(12)฀natural฀enemies฀ found,฀and฀(13)฀decision฀and฀recommendation฀summary. We฀ offer฀ the฀ following฀ feasibility฀ study฀ of฀air฀potato฀(Dioscorea฀bulbifera฀L.;฀Dioscoreaceae),฀an฀invasive฀weed฀of฀natural฀ vegetation฀in฀Florida,฀as฀a฀working฀model฀ of฀the฀approach.฀In฀addition฀to฀weed฀biological฀control,฀we฀think฀that฀with฀modification,฀the฀feasibility฀study฀presented฀here฀ can฀ be฀ useful฀ and฀ appropriate฀ for฀ insect฀ biological฀control. Nature of damage Dioscorea฀ bulbifera฀ is฀ an฀ herbaceous,฀ perennial฀ twining฀ vine฀ 20฀ m฀ or฀ more,฀ capable฀ of฀ climbing฀ and฀ out-competing฀ native฀vegetation฀(e.g.,฀Schmitz฀et฀al.฀1997;฀ Langeland฀ and฀ Craddock฀ Burks฀ 1998;฀ Gordon฀et฀al.฀1999).฀Dioscorea฀bulbifera฀ was฀ introduced฀ to฀ Florida฀ from฀ tropical฀ Asia฀ or฀ Africa฀ in฀ 1905฀ (Morton฀ 1976)฀ and฀ now฀ constitutes฀ one฀ of฀ the฀ most฀ aggressive฀weeds฀ever฀introduced฀to฀Florida฀ (Hammer฀1998).฀The฀noted฀horticulturalist฀ Henry฀Nehrling฀was฀apparently฀the฀first฀to฀ express฀concern฀for฀its฀invasiveness,฀stating฀that฀“with฀the฀exception฀of฀the฀kudzu฀ vine฀I฀have฀never฀seen฀a฀more฀aggressive฀ and฀dangerous฀vine฀in฀Florida”฀(Nehrling฀ 1933).฀ Similar฀ warnings฀ were฀ expressed฀ 270 Natural Areas Journal in฀the฀1970s฀(Long฀and฀Lakela฀1976)฀with฀ recommendations฀to฀limit฀the฀planting฀of฀ this฀ ornamental฀ species฀ (Morton฀ 1976;฀ Ward฀1977).฀By฀the฀1980s,฀this฀vine฀was฀ found฀growing฀in฀thickets,฀waste฀areas,฀and฀ hedge฀ or฀ fencerows฀ in฀ south฀ and฀ central฀ Florida฀(Bell฀and฀Taylor฀1982).฀By฀1999,฀ D.฀ bulbifera฀ was฀ listed฀ in฀ Florida฀ as฀ a฀ noxious฀weed฀by฀the฀Florida฀Department฀ of฀ Agricultural฀ and฀ Consumer฀ Services฀ (FDACS)฀ (FLEPPC฀ 2003).฀ Dioscorea฀ bulbifera฀ is฀ considered฀ the฀ most฀ serious฀ type฀of฀environmental฀threat,฀described฀as฀a฀ Category฀I฀weed฀by฀the฀Florida฀Exotic฀Pest฀ Plant฀Council฀(FLEPPC)฀(FLEPPC฀2003),฀ “invasive฀ exotics฀ that฀ are฀ altering฀ native฀ plant฀ communities฀ by฀ displacing฀ native฀ species,฀ changing฀ community฀ structures฀ or฀ ecological฀ functions,฀ or฀ hybridizing฀ with฀ natives.”฀ Presently,฀ D.฀ bulbifera฀ is฀ well฀ established฀ in฀ Florida฀ and฀ probably฀ throughout฀ the฀ Gulf฀ states฀ (Raz฀ 2002)฀ where฀it฀has฀the฀potential฀to฀severely฀disrupt฀ entire฀ecosystems฀(Hammer฀1998). Ecological damage The฀primary฀ecological฀threat฀D.฀bulbifera฀ poses฀to฀natural฀areas฀is฀its฀ability฀to฀climb฀ and฀eventually฀out-compete฀native฀vegetation฀for฀limited฀resources฀(Schmitz฀1994;฀ Langeland฀ and฀ Craddock฀ Burks฀ 1998;฀ Gordon฀ et฀ al.฀ 1999).฀ D.฀ bulbifera฀ is฀ one฀ of฀ the฀ more฀ common฀ natural฀ area฀ weeds฀ in฀ central฀ and฀ south฀ Florida.฀ In฀ south฀ Florida,฀the฀weed฀occurs฀in฀15.2%฀of฀315฀ of฀the฀conservation฀areas฀and฀25%฀of฀48฀of฀ the฀habitats฀surveyed฀(compared฀with฀the฀ most฀common฀natural฀area฀weed฀Brazilian฀ pepper,฀ Schinus฀ terebinthifolius฀ Raddi,฀ reported฀from฀65.4%฀of฀the฀conservation฀ areas฀and฀83.3%฀of฀the฀habitats;฀Gann฀et฀ al.฀2001).฀In฀south฀Florida,฀D.฀bulbifera฀is฀ frequently฀found฀in฀tropical฀and฀subtropical฀ hammocks฀but฀may฀also฀invade฀disturbed฀ uplands,฀ scrub,฀ sinkholes,฀ alluvial฀ flood฀ plain฀forests,฀and฀urban฀lots฀(Schultz฀1993;฀ Gann฀et฀al.฀2001).฀Evidence฀also฀suggests฀ that฀ D.฀ bulbifera฀ aggressively฀ exploits฀ disturbed฀ sites,฀ such฀ as฀ forest฀ canopies฀ damaged฀by฀hurricanes,฀and฀impedes฀the฀ reestablishment฀by฀native฀species฀(Horvitz฀ et฀al.฀1998;฀Gordon฀et฀al.฀1999).฀This฀species฀has฀a฀profound฀long-term฀impact฀on฀ the฀community฀structure฀by฀invading฀and฀ maintaining฀these฀sites฀following฀hurricane฀ disturbance฀(Gordon฀et฀al.฀1999). Economic damage Presently,฀control฀of฀D.฀bulbifera฀populations฀ is฀ limited฀ to฀ manual,฀ herbicidal,฀ or฀ a฀combination฀of฀these฀two฀methods฀with฀ only฀limited฀efficacy.฀Manual฀removal฀of฀ aboveground฀ plants฀ and฀ bulbils฀ (aerial฀ tubers)฀ has฀ become฀ a฀ common฀ activity฀ employed฀ by฀ diverse฀ volunteer฀ groups฀ (Duxbury฀ et฀ al.฀ 2003).฀ Manual฀ removal฀ of฀ plants฀ and฀ bulbils฀ was฀ found฀ to฀ be฀ as฀ effective฀ at฀ controlling฀ D.฀ bulbifera฀ as฀ a฀ combination฀of฀herbicide฀(e.g.฀Roundup)฀ and฀ hand฀ pulling฀ (Gordon฀ et฀ al.฀ 1999).฀ If฀ mechanical฀ removal฀ is฀ not฀ an฀ option,฀ chemical฀ control฀ of฀ vines฀ requires฀ repeated฀ basal฀ applications฀ of฀ herbicides฀ (e.g.,฀ Roundup,฀ Remedy,฀ or฀ 50%฀ Garlon฀ 3A),฀ and฀ these฀ treatments฀ need฀ to฀ be฀ repeated฀ over฀ a฀ 2฀ or฀ 3฀ y฀ period฀ (Mullahey฀ and฀Brown฀1999).฀Herbicidal฀control฀with฀ Roundup฀ and฀ Rodeo฀ of฀ heavily฀ infested฀ areas฀(e.g.,฀Fern฀Forest,฀Broward฀County,฀ Florida)฀that฀included฀other฀invasive฀weeds฀ (e.g.฀S.฀terebinthifolius,฀Bischofia฀trifoliate฀ (Roxb.))฀cost฀$1,750/ha/y.฀In฀this฀example,฀ complete฀control฀was฀not฀achieved฀as฀resprouts฀continued฀despite฀three฀herbicide฀ treatments฀ during฀ nearly฀ 2฀ y.฀A฀ resident฀ biologist฀ (Pat฀ Howell,฀ Broward฀ County฀ Parks฀ and฀ Recreation,฀ pers.฀ comm.)฀ estimated฀ that฀ 5฀ y฀ or฀ more฀ of฀ herbicidal฀ control฀ and฀ monitoring฀ will฀ be฀ required.฀ The฀herbicidal฀control฀has฀additional฀costs฀ as฀non-target฀species,฀such฀as฀natives,฀may฀ be฀injured฀due฀to฀the฀non-selective฀nature฀ of฀these฀products. Area of origin and geographic distribution D.฀ bulbifera฀ is฀ native฀ to฀ and฀ widely฀ distributed฀in฀Asia฀and฀Africa฀(Burkill฀1960;฀ Coursey฀1967;฀Tindall฀1993).฀Cultivated฀D.฀ bulbifera฀was฀first฀brought฀from฀the฀Pacific฀ to฀India฀in฀the฀middle฀of฀the฀19th฀century฀ and฀from฀there฀cultivars฀were฀introduced฀ to฀Europe฀(Burkill฀1960).฀In฀the฀Western฀ Hemisphere,฀it฀is฀widely฀naturalized฀in฀the฀ tropics฀and฀subtropics฀of฀the฀West฀Indies,฀ Central,฀ and฀ South฀ America฀ (McVaugh฀ 1989;฀ Schultz฀ 1993).฀ Further฀ research฀ Volume 27 (3), 2007 is฀ required฀ to฀ determine฀ which฀ cultivar฀ is฀ invasive฀ in฀ North฀ America.฀ Presently,฀ studies฀are฀underway฀to฀identify฀the฀origin฀ of฀ the฀ invasive฀ variety฀ of฀ D.฀ bulbifera฀ in฀ Florida฀through฀chloroplast฀DNA฀analysis฀ (Overholt฀ et฀ al.฀ 2003).฀ Possibly฀ the฀ best฀ adapted฀biological฀control฀agents฀will฀be฀ imported฀ from฀ the฀ area฀ of฀ origin฀ of฀ the฀ invasive฀D.฀bulbifera฀variety. Since฀ its฀ introduction฀ to฀ Florida,฀ D.฀ bulbifera฀has฀aggressively฀spread฀throughout฀ the฀state.฀From฀the฀northwestern฀panhandle,฀ Escambia฀County,฀to฀the฀southern฀tip฀of฀the฀ state,฀collections฀from฀herbaria฀and฀reports฀ from฀ state฀ regional฀ biologists฀ have฀ listed฀ 29฀of฀67฀Florida฀counties฀infested฀with฀D.฀ bulbifera฀(Schmitz฀1994;฀Gann฀et฀al.฀2001;฀ Wunderlin฀and฀Hansen฀2003).฀This฀species฀ has฀ also฀ been฀ reported฀ to฀ be฀ naturalized฀ in฀Mississippi,฀Louisiana,฀Texas,฀Hawaii,฀ central฀ and฀ southern฀ Mexico฀ (Colima,฀ Mexico,฀Puebla,฀Veracruz,฀San฀Luis฀Potosi,฀ Oaxaca,฀and฀Chiapas฀states),฀and฀the฀West฀ Indies฀(USDA/SCS฀1982;฀McVaugh฀1989;฀ Nesom฀ and฀ Brown฀ 1998;฀ USDA/NRCS฀ 2002).฀ It฀ is฀ reported฀ to฀ be฀ established฀ in฀ Central฀ and฀ northern฀ South฀ America฀ (Tellez฀ and฀ Schubert฀ 1994;฀ Bennett฀ and฀ Prance฀2000). Identification The฀identity฀of฀Florida฀populations฀of฀D.฀ bulbifera฀was฀recently฀verified฀by฀L.฀Raz,฀ an฀ authority฀ on฀ the฀ Dioscoreaceae฀ (Raz฀ 2002).฀Leaves฀are฀simple,฀alternate,฀blades฀ broadly฀ovate-cordate,฀cuspidate,฀4-20฀cm฀ long฀and฀wide,฀prominently฀7-11฀nerved,฀ glabrous,฀ and฀ entire฀ (Schultz฀ 1993;฀ Raz฀ 2002).฀More฀details฀can฀be฀found฀in฀Tindall฀ (1993)฀ and฀ Hammer฀ (1998).฀ In฀ Florida,฀ bulbils฀ form฀ in฀ August฀ and฀ drop฀ to฀ the฀ ground฀in฀November฀to฀December฀(Mullahey฀ and฀ Brown฀ 1999)฀ and฀ may฀ weigh฀ as฀much฀as฀1฀kg,฀though฀300฀g฀bulbils฀are฀ more฀ common฀ (Degras฀ 1993).฀The฀ vines฀ die฀back฀during฀the฀cooler฀months,฀even฀in฀ the฀frost-free฀regions฀of฀southern฀Florida,฀ and฀ regrow฀ during฀ the฀ spring.฀ In฀ south฀ Florida,฀ D.฀ bulbifera฀ vines฀ may฀ grow฀ to฀ 20฀m฀or฀more฀from฀underground฀tubers฀or฀ bulbils฀produced฀in฀leaf฀axils฀(Langeland฀ and฀Craddock฀Burks฀1998).฀While฀flowers฀ are฀ produced฀ in฀ the฀ plant’s฀ native฀ range฀ Volume 27 (3), 2007 (Tindall฀1993),฀they฀have฀only฀rarely฀been฀ seen฀in฀Florida฀(Schultz฀1993)฀and฀when฀ they฀do฀appear,฀they฀are฀considered฀infertile฀ (Gordon฀et฀al.฀1999).฀The฀primary฀means฀ of฀spreading฀is฀through฀human฀movement฀ of฀bulbils฀(Schultz฀1993). The฀Dioscorea฀species฀(D.฀alata,฀D.฀bulbifera,฀D.฀polystachya฀(=D.฀oppositifolia),฀ and฀ D.฀ sansibarensis)฀ naturalized฀ in฀ the฀ United฀States฀(Table฀1)฀all฀produce฀tubers฀ (enlarged฀underground฀stem,฀typically฀vertically฀oriented)฀and฀can฀be฀distinguished฀ from฀the฀native฀species฀(D.฀floridana฀and฀D.฀ villosa),฀which฀produce฀rhizomes฀(horizontal฀underground฀stems).฀Furthermore,฀the฀ naturalized฀species฀have฀aerial฀bulbils฀in฀the฀ leaf฀axils,฀which฀are฀lacking฀in฀the฀native฀ species฀(Raz฀2002;฀Wunderlin฀and฀Hansen฀ 2003).฀ D.฀ bulbifera฀ can฀ be฀ distinguished฀ from฀the฀three฀other฀naturalized฀Dioscorea฀ species฀(D.฀alata,฀D.฀polystachya,฀and฀D.฀ sansibarensis)฀that฀occur฀in฀Florida฀by฀its฀ unwinged฀stems,฀with฀alternate฀leaves฀that฀ are฀entire,฀and฀leaf฀length฀less฀than฀20฀cm.฀ D.฀ alata฀ has฀ winged฀ stems฀ and฀ opposite฀ leaves;฀ D.฀ polystachya฀ has฀ leaf฀ margins฀ that฀ are฀ irregularly฀ three-five฀ lobed;฀ D.฀ sansibarensis฀has฀large฀leaves฀to฀46฀cm฀in฀ length฀(Raz฀2002;฀Wunderlin฀and฀Hansen฀ 2003).฀The฀two฀Dioscorea฀species฀native฀to฀ Florida฀and฀the฀United฀States฀(D.฀floridana฀ and฀D.฀villosa)฀are฀low-climbing฀vines฀less฀ than฀3฀m฀in฀length฀(Raz฀2002;฀Wunderlin฀ and฀Hansen฀2003). Taxonomy and analysis of related plants The฀family฀Dioscoreaceae฀includes฀either฀ four฀(Caddick฀et฀al.฀2002b)฀or฀seven฀genera฀(Al-Shehbaz฀and฀Schubert฀1989;฀Raz฀ 2002).฀ The฀ largest฀ genus฀ in฀ the฀ family,฀ Dioscorea,฀ contains฀ approximately฀ 600฀ species฀(Raz฀2002)฀(850฀species฀according฀ to฀Al-Shehbaz฀and฀Schubert฀1989),฀most฀ of฀which฀grow฀in฀the฀subtropics฀or฀tropics,฀ with฀ only฀ a฀ few฀ species฀ growing฀ in฀ the฀ warmer฀temperate฀regions฀(Al-Shehbaz฀and฀ Schubert฀1989;฀Raz฀2002).฀In฀the฀Western฀ Hemisphere,฀approximately฀130฀Dioscorea฀ species฀occur฀in฀Brazil฀and฀120฀in฀Central฀ America฀ and฀ Mexico฀ (Al-Shehbaz฀ and฀ Schubert฀ 1989).฀ The฀ most฀ comprehensive฀treatment฀of฀the฀Mexican฀ Dioscorea฀ included฀ 63฀ species฀ (Matuda฀ 1953).฀ In฀ only฀ Mesoamerica,฀ 46฀ species฀ names฀ have฀been฀accepted฀(Tellez฀and฀Schubert฀ 1994).฀Only฀six฀ Dioscorea฀species฀occur฀ in฀the฀southeastern฀U.S.฀(Al-Shehbaz฀and฀ Schubert฀ 1989;฀ Raz฀ 2002)฀ and,฀ of฀ these,฀ four฀are฀naturalized฀from฀Asia฀and฀two฀are฀ native฀(Raz฀2002;฀Table฀1). The฀ Dioscorea฀ genus฀ is฀ grouped฀ into฀ subgeneric฀sections.฀The฀two฀native฀North฀ American฀ (north฀ of฀ Mexico)฀ species,฀ D.฀ floridana฀ (Florida฀ yam)฀ and฀ D.฀ villosa฀ (wild฀ yam),฀ are฀ assigned฀ to฀ the฀ section฀ Macropoda฀ (Knuth฀ 1924;฀ Raz฀ 2002).฀ Traditionally฀D.฀bulbifera฀has฀been฀placed฀ in฀ section฀ Opsophyton฀ along฀ with฀ other฀ tropical฀Old฀World฀species฀(Knuth฀1924;฀ Huber฀1998).฀Recent฀phylogenetic฀analysis฀ based฀on฀sequence฀data฀from฀two฀plastid฀ genes฀placed฀this฀species฀in฀the฀mostly฀Old฀ World฀‘B’฀clade฀and฀within฀a฀lower฀level฀ compound-leaf฀ subclade฀ (CL)฀ (Wilkin฀ et฀ al.฀2005).฀This฀analysis฀did฀not฀include฀the฀ two฀ native฀ U.S.฀ Dioscorea฀ species฀ (Raz฀ 2002).฀However,฀other฀results฀indicate฀that฀ the฀two฀native฀species฀should฀be฀placed฀in฀ the฀ Stenophora฀ subclade฀ of฀Wilkin฀ et฀ al.฀ (2005;฀L.฀Raz,฀unpubl.฀data). Rajania,฀ an฀ endemic฀ genus฀ in฀ the฀ West฀ Indies฀(Raz฀2002),฀is฀the฀only฀other฀genus฀ of฀the฀Dioscoreaceae฀in฀the฀region฀(Table฀ 2).฀Members฀of฀this฀genus฀produce฀an฀indehiscent฀samara฀and฀can฀be฀distinguished฀ from฀ members฀ of฀ the฀ Dioscorea,฀ which฀ produce฀capsular฀fruit฀(Huber฀1998).฀Although฀this฀genus฀is฀being฀revised฀(L.฀Raz,฀ unpubl.฀data),฀the฀center฀of฀origin฀appears฀ to฀ be฀ Cuba฀ with฀ 19฀ species฀ distributed฀ throughout฀the฀West฀Indies฀(Knuth฀1924;฀ Raz฀ 2002).฀ Recent฀ phylogenetic฀ analysis฀ based฀upon฀molecular฀sequence฀data฀suggests฀ that฀ the฀ Rajania฀ genus฀ should฀ be฀ subsumed฀into฀the฀much฀larger฀Dioscorea฀ genus฀ (Caddick฀ et฀ al.฀ 2002a;฀ Wilken฀ et฀ al.฀2005).฀Until฀the฀formal฀nomenclatural฀ transfers฀can฀be฀completed,฀we฀continue฀to฀ use฀the฀traditional฀generic฀epithet฀Rajania฀ (L.฀Raz,฀unpubl.฀data). Potential conflicts of interest, economically important species The฀Dioscorea฀genus฀includes฀several฀im- Natural Areas Journal 271 272 Natural Areas Journal Table฀1.฀North฀American฀and฀West฀Indian฀Dioscorea฀spp.฀that฀are฀native,฀naturalized,฀or฀cultivated.฀List฀compiled฀from฀various฀sources฀including฀the฀USDA,฀NRCS฀Plants฀database฀and฀SIIT฀ 2003.฀Taxonomy฀follows฀that฀of฀the฀Missouri฀Botanical฀Garden฀Tropicos,฀Nomenclatural฀Data฀Base. Scientific name Section Common name Occurrence in NA & WI1 Comments Origin A. Species native to the continental US Dioscorea floridana Bartlett Macropoda Florida yam FL,GA,SC native SE U.S. 9 D. villosa L. (including D. quaternata J.F. Gmel.) Macropoda wild yam Eastern U.S. north to CT, south to FL, and west to NE native E. U. S. 9 B. Species of concern in Mexico and the West Indies Volume 27 (3), 2007 Dioscorea alata L. Enantiophyllum water yam FL,Puerto Rico,Virgin Islands, Cuba, Hispaniola, Bahamas, Jamaica naturalized Trop. E. Asia 3 D. altissima Lam. Chondrocarpa dunguey Hispaniola, Puerto Rico, Cuba, Lesser Antilles native South America 10 D. bulbifera L. (includes D. latifolia Benth.) Opsophyton air yam FL, MS, LA, TX, Bahamas, Puerto Rico, Cuba, Hispaniola, Jamaica, Cent. & So. Mexico naturalized Trop. Old World 3 D. cayenensis Lam. (includes D. occidentalis R. Knuth. in part) Enantiophyllum yellow guinea yam Hispaniola, Puerto Rico, Cuba, Jamaica naturalized Africa 3 D. convolvulacea Cham. & Schldl. Trigonobasis (Zhizum) yam Mexico cultivated Central America 3 D. convolvulacea Schlecht. & Cham. Trigonobasis So. & West Mexico (pos. Tamaulipas) native Central America 3 D. cubensis R. Knuth.2 Lynchnostemon Cuba native Cuba 5, 10 D. dodecaneura Vell. Lasiogyne FL naturalized South America D. dumetorum (Kunth) Pax (includes D. tryphylla L.) Lasiophyton bitter yam Cuba, Jamaica, Hispaniola naturalized Africa 3 D. esculenta (Lour.) Burkill Combilium lesser yam Hispaniola (as D. sativa ?), Puerto Rico, Cuba cultivated Indo-China 3 yam Mexico, Central America cultivated Mexico, Central America 4 D. floribunda C. Martius & Galeotti (continued) Volume 27 (3), 2007 Table฀1.฀Continued. Natural Areas Journal 273 Occurrence in NA & WI1 Comments Origin S. West Mexico (pos. Tamaulipas) native S. W. Mexico (pos. Tamaulipas)8 bulbous yam Hispaniola, Puerto Rico, Virgin Islands, Lesser Antilles native South or Central America mata gallina, gunda, bitter Jesse Cuba, Hispaniola, Puerto Rico, Jamaica, Lesser Antilles native South America, West Indies or Central America So. to West Mexico (pos. Tamaulipas) native S. to W. Mexico (pos. Tamaulipas) 9 Eastern U.S. north to CT, south to GA, and west to MO naturalized E. Asia 9 Lynchnostemon Cuba native Cuba 10 D. remotiflora Knuth. Macrogynodium So. to West Mexico (pos. Tamaulipas) native So. to West Mexico (pos. Tamaulipas)8 D. rotundata Poir. (includes D. occidentalis R. Knuth. in part) Enantiophyllum Guinea yam Puerto Rico, Jamaica cultivated Africa 3 D. sansibarensis Pax Opsophyton Zanzibar yam FL naturalized Africa 3 D. tamoidea Griseb.2 Lynchnostemon Cuba, Hispaniola native West Indies 5 D. trifida L. Macrogynodium Hispaniola, Jamaica, Puerto Rico, Cuba cultivated N. South America 3, 5 D. wrightii Uline2 (includes D. heradurensis (R. Knuth) P. Wilson 10) Lynchnostemon Cuba native Cuba 5 Scientific name Section D. militaris B.L. Rob. Trigonobasis D. pilosiuscula Bertero ex Spreng. Dematostemon D. polygonoides Humb. & Bonpl. ex Willd. Lynchnostemon D. remotiflora Knuth. Macrogynodium D. polystachya Turcz. (including D. oppositifolia Thunb.) Enantiophyllum D. ravenii Ayala (including D. grisebachii Knuth 10) 1 Common name Cinnamon yam, Chinese yam Indian yam, mapuey, yampi, cush-cush U.S. state abbreviations. 2 Name not included in the Missouri Botanical Garden, Tropicos, Nomenclatural Data Base. Dioscorea section Lychnostemon also includes an unpublished species from Cuba. 3 Burkill 1960; 4 Knuth 1924; 5 Leon & Alain 1974; 6 Martin 1969; 7 MBG 2003; 8 McVaugh 1989; 9 Raz 2002; 10 Raz unpublished data. portant฀species฀that฀have฀been฀used฀around฀ the฀world฀for฀food฀(Martin฀1974;฀Mabberley฀1997).฀In฀1972,฀it฀was฀estimated฀that฀ 5443฀metric฀tons฀of฀yams฀were฀imported฀ into฀the฀United฀Kingdom฀from฀West฀Africa฀ and฀ the฀ West฀ Indies฀ (Purseglove฀ 1972).฀ However,฀the฀importance฀of฀many฀of฀these฀ yams฀ for฀ food฀ has฀ declined฀ substantially฀ because฀ of฀ the฀ introduction฀ of฀ alternate฀ food฀crops฀(Purseglove฀1972).฀The฀species,฀ D.฀alata,฀was฀also฀introduced฀to฀Georgia฀ (Raz฀ 2002)฀ and฀ South฀ Florida฀ (Young฀ 1923;฀Raz฀2002)฀where฀some฀modest฀home฀ garden฀use฀may฀still฀occur,฀and฀it฀may฀still฀ be฀ used฀ as฀ food฀ (Hammer฀ 1998).฀ However,฀like฀D.฀bulbifera,฀D.฀alata฀is฀widely฀ naturalized฀ in฀ Florida฀ where฀ it฀ has฀ been฀ reported฀ from฀ nine฀ counties฀ (Wunderlin฀ and฀ Hansen฀ 2003),฀ and฀ is฀ considered฀ a฀ FLEPPC฀ Category฀ I฀ species฀ (FLEPPC฀ 2003).฀ D.฀ alata฀ is฀ likely฀ to฀ be฀ found฀ escaped฀from฀cultivation฀in฀other฀areas฀in฀the฀ southeastern฀United฀States฀(Raz฀2002).฀To฀ our฀knowledge,฀no฀Dioscorea฀species฀are฀ Table฀2.฀Caribbean฀Rajania฀spp.฀compiled฀from฀various฀sources1.฀The฀genus฀Rajania฀is฀being฀subsumed฀ into฀Dioscorea2.฀However,฀the฀traditional฀use฀is฀applied฀here฀until฀this฀revision฀is฀published. Scientific name 3 Common name Occurrence 1 R. angustifolia Sw. Ñame cimarron Hispaniola R. cephalocarpa Uline ex R.Knuth R. cordata L. Cuba Ñame de la India, Jamaica, Puerto Rico, himber, Hispaniola, Lesser wa-wa Antilles R. ekmanii Knuth Cuba R. hastata L. (includes R. microphylla Knuth 3) Hispaniola R. microphylla Kunth Ñame mambi R. nipensis Howard. R. ovata Sw. Cuba, Bahamas Cuba Ñame cimarron Cuba, Hispaniola R. pilifera Urb. Hispaniola R. porulosa R.Knuth Cuba R. psilostachya (Knuth) Uline ex R. Knuth Cuba R. quinquefolia L. Catyame Cuba, Hispaniola R. spiculiflora Hispaniola R. tenella Howard Cuba R. tenuiflora R. Knuth Lampina R. theresensis Uline ex R.Knuth R. wrightii Uline ex R. Knuth Cuba, Hispaniola Cuba Ñame cimarron Cuba 1 Adams 1972; Leon and Alain 1974; Correll and Correll 1982; Liogier and Martorell 1982; Liogier 2000. 2 Raz (unpublished data). Only R. cordata L., R. hastata L., and R. linearis (Griseb.) R.A. Howard are recognized by the Missouri Botanical Garden, Tropicos, Nomenclatural Data Base. This table includes all published names currently recognized by Raz (ms in prep.). Rajania also includes two unpublished species from Cuba and the Domincan Republic, respectively. Varietal names are not listed here. 3 274 Natural Areas Journal cultivated฀commercially฀as฀food฀crops฀in฀ Florida฀or฀the฀southeastern฀U.S. Another฀Dioscorea฀introduction฀to฀South฀ Florida฀includes฀D.฀sansibarensis฀or฀Zanzibar฀yam฀that฀has฀been฀reported฀rarely฀(Raz฀ 2002;฀USDA/NRCS฀2002;฀Wunderlin฀and฀ Hansen฀2003).฀The฀few฀known฀populations฀ of฀D.฀sansibarensis฀have฀been฀eradicated฀ (Hammer,฀Miami฀Dade฀Parks฀and฀Recreation,฀ pers.฀ comm.).฀Another฀ exotic฀ species,฀D.฀polystachya฀(as฀D.฀oppositifolia;฀ sensu,฀ Al-Shehbaz฀ and฀ Schubert฀ 1989),฀ is฀ native฀ to฀ eastern฀Asia฀ where฀ it฀ is฀ cultivated฀for฀food.฀In฀the฀U.S.,฀this฀species฀ has฀ become฀ naturalized฀ in฀ many฀ states฀ (North฀Carolina,฀South฀Carolina,฀Georgia,฀ Tennessee,฀Alabama,฀and฀Arkansas)฀where฀ it฀ was฀ introduced฀ as฀ an฀ ornamental฀ (AlShehbaz฀ and฀ Schubert฀ 1989;฀ Raz฀ 2002).฀ D.฀ polystachya฀ now฀ represents฀ a฀ severe฀ threat฀to฀native฀plant฀communities฀in฀Tennessee฀(SEEPPC฀2001;฀Pemberton฀2002;฀ Tu฀ 2002).฀ Recently฀ a฀ South฀ American฀ species,฀D.฀dodecaneura฀Vell.,฀was฀sold฀in฀ a฀nursery฀in฀north฀Florida.฀Although฀this฀ species฀does฀not฀produce฀bulbils฀and฀only฀ staminate฀plants฀are฀known฀in฀our฀range,฀its฀ aggressive฀growth฀prompted฀discontinued฀ sales฀(L.฀Raz,฀unpubl.฀data). Members฀ of฀ the฀ Dioscorea฀ genus฀ are฀ of฀ greater฀economic฀importance฀in฀the฀West฀ Indies฀where฀several฀species฀are฀still฀cultivated฀ (Martin฀ 1974;฀ Perez฀ et฀ al.฀ 2005;฀ Table฀1).฀D.฀alata฀has฀been฀grown฀historically฀in฀the฀region฀and฀it฀still฀occurs฀in฀the฀ Bahamas฀(Correll฀and฀Correll฀1982),฀Cuba฀ (Leon฀and฀Alain฀1974),฀Hispaniola฀(Liogier฀2000),฀Jamaica฀(Adams฀1972),฀Puerto฀ Rico฀ (Liogier฀ and฀ Martorell฀ 1982),฀ and฀ the฀ Virgin฀ Islands฀ (USDA/NRCS฀ 2002).฀ D.฀cayenensis฀(reported฀as฀D.฀occidentalis฀ in฀ Leon฀ and฀Alain฀ 1974)฀ is฀ cultivated฀ in฀ Cuba,฀Jamaica฀(L.฀Raz,฀pers.฀observation),฀ and฀ Puerto฀ Rico฀ (Liogier฀ and฀ Martorell฀ 1982).฀D.฀trifida฀remains฀an฀important฀crop฀ in฀the฀Lesser฀Antilles฀(Degras฀1993),฀and฀ D.฀ dumetorum฀ has฀ been฀ reported฀ (as฀ D.฀ triphylla฀ in฀ Leon฀ and฀ Alain฀ 1974)฀ from฀ Cuba.฀Finally,฀D.฀esculenta฀is฀cultivated฀in฀ Puerto฀Rico฀(Liogier฀and฀Martorell฀1982)฀ and฀Cuba฀(Perez฀et฀al.฀2005).฀At฀least฀four฀ food฀yams฀(D.฀alata,฀D.฀cayenensis฀and฀D.฀ cayenensis฀subsp.฀rotundata฀and฀D.฀trifida)฀ are฀ imported฀ to฀ the฀ United฀ States฀ from฀ Volume 27 (3), 2007 Latin฀America,฀primarily฀Costa฀Rica,฀and฀ are฀sold฀in฀supermarkets฀and฀ethnic฀grocery฀ stores฀catering฀to฀Hispanic฀and฀West฀Indian฀ people฀(Pemberton,฀unpubl.฀data). Potential risks of biological control to native plants In฀ addition฀ to฀ the฀ two฀ native฀ species฀ D.฀ floridana฀and฀D.฀villosa฀(Raz฀2002),฀a฀third฀ species,฀D.฀quaternata฀(fourleaf฀yam),฀has฀ been฀listed฀by฀some฀authors฀(Al-Shehbaz฀ and฀Schubert฀1989;฀USDA/NRCS฀2002).฀ However,฀ more฀ recent฀ treatments฀ of฀ the฀ North฀ American฀ species฀ subsumed฀ D.฀ quaternata฀ into฀ D.฀ villosa฀ based฀ upon฀ significant฀ phenotypic฀ variability฀ within฀ the฀complex฀without฀any฀apparent฀natural฀ gaps฀in฀the฀variation฀(Raz฀2002;฀Wunderlin฀ and฀Hansen฀2003).฀D.฀floridana฀occurs฀in฀ Florida,฀Georgia,฀and฀South฀Carolina฀(Raz฀ 2002;฀USDA/NRCS฀2002;฀Wunderlin฀and฀ Hansen฀2003).฀D.฀villosa฀occurs฀in฀Florida,฀ north฀ to฀ Connecticut฀ and฀ west฀ to฀ Texas,฀ and฀Minnesota฀(Al-Shehbaz฀and฀Schubert฀ 1989;฀ Raz฀ 2002;฀ USDA/NRCS฀ 2002;฀ Wunderlin฀and฀Hansen฀2003). The฀West฀Indies฀has฀greater฀native฀species฀ diversity฀of฀both฀the฀Dioscorea฀and฀Rajania฀ genera฀ than฀ North฀America,฀ north฀ of฀ Mexico.฀The฀West฀ Indian฀ Dioscorea฀ and฀ Rajania฀are฀currently฀in฀revision฀and฀the฀ numbers฀of฀species฀given฀here฀are฀unpublished฀ estimates฀ (L.฀ Raz,฀ unpubl.฀ data).฀ There฀are฀nine฀native฀Dioscorea฀spp.฀and฀ 19฀species฀of฀the฀endemic฀genus฀Rajania฀ from฀ the฀ West฀ Indies฀ (Knuth฀ 1924;฀ Raz฀ 2002;฀ L.฀ Raz,฀ unpubl.฀ data)฀ with฀ their฀ greatest฀diversity฀in฀Cuba฀(Leon฀and฀Alain฀ 1974;฀L.฀Raz,฀unpubl.฀data).฀None฀of฀these฀ West฀ Indian฀ Dioscorea฀ species฀ is฀ placed฀ in฀the฀section฀Opsophyton฀with฀the฀weed฀ D.฀bulbifera฀(Table฀1). The฀greatest฀diversity฀of฀this฀group฀in฀our฀ area฀occurs฀in฀Mexico฀and฀Central฀America,฀ with฀about฀60฀native฀species฀of฀Dioscorea,฀ (Matuda฀1953;฀Tellez฀and฀Schubert฀1994).฀ For฀ our฀ purposes,฀ the฀ Dioscorea฀ species฀ that฀ occur฀ in฀ the฀ northern฀ extent฀ of฀ this฀ range,฀along฀the฀Texas฀border฀in฀the฀states฀ of฀Chihuahua,฀Coahuila,฀Nuevo฀Leon,฀and฀ Tamaulipas,฀ Mexico,฀ would฀ be฀ the฀ most฀ relevant.฀ Dioscorea฀ species฀ that฀ occur฀ in฀ Volume 27 (3), 2007 these฀ states฀ that฀ are฀ hosts฀ of฀ biological฀ control฀agents฀could฀potentially฀provide฀a฀ bridge฀ between฀ D.฀ bulbifera฀ populations฀ in฀Texas฀to฀more฀southern฀Dioscorea฀species฀in฀the฀state฀of฀Veracruz,฀Mexico,฀and฀ southward.฀ The฀ only฀ Dioscorea฀ species฀ known฀from฀this฀northern฀‘bridging฀area’฀ are฀ D.฀ convolvulacea฀ (Barrera฀ 1990),฀ D.฀ militaris,฀ and฀ D.฀ remotiflora฀ (McVaugh฀ 1989)฀and฀these฀are฀only฀reported฀from฀the฀ state฀of฀Tamaulipas,฀just฀south฀of฀the฀Texas฀ border.฀ Like฀ the฀ West฀ Indian฀ Dioscorea฀ species,฀the฀more฀geographically฀proximate฀ Mexican฀Dioscorea฀species฀belong฀to฀different฀taxonomic฀sections฀than฀D.฀bulbifera฀ (Table฀1),฀and฀phylogenetic฀studies฀based฀ on฀plastid฀DNA฀(L.฀Raz,฀in฀prep.)฀do฀not฀ suggest฀affinities฀of฀D.฀bulbifera฀with฀any฀ of฀these฀Mexican฀yam฀species. In฀Texas,฀D.฀bulbifera฀is฀not฀known฀to฀be฀ widespread฀(B.L.฀Turner฀and฀T.฀Wendt,฀University฀of฀Texas;฀and฀M.D.฀Reed,฀TAMU฀ herbarium,฀Texas฀A&M฀ University,฀ pers.฀ comm.).฀However,฀a฀few฀scattered฀specimens฀have฀been฀collected฀from฀wild฀plant฀ populations฀ (USDA/NRCS฀ 2002)฀ in฀ the฀ eastern฀part฀of฀the฀state฀(Nesom฀and฀Brown฀ 1998).฀As฀D.฀bulbifera฀is฀not฀reported฀to฀ be฀present฀in฀Texas,฀it฀is฀doubtful฀that฀any฀ releases฀of฀control฀agents฀will฀occur฀there.฀ However,฀ if฀ an฀ introduced฀ control฀ agent฀ was฀ to฀ establish฀ in฀ this฀ area฀ of฀ Texas,฀ it฀ would฀have฀to฀travel฀a฀distance฀of฀~320฀km฀ from฀the฀Houston฀area฀to฀the฀Tamaulipas฀ state฀ of฀ Mexico฀ to฀ encounter฀ one฀ of฀ the฀ native฀Dioscorea฀species. Secondary plant chemistry and its relevance to herbivory and pathogens In฀addition฀to฀geographic฀and฀taxonomic฀ barriers฀ to฀ dietary฀ breadth฀ in฀ herbivores฀ introduced฀ for฀ biological฀ control฀ of฀ D.฀ bulbifera,฀ the฀ choice฀ of฀ host฀ plant฀ species฀ may฀ be฀ limited฀ by฀ the฀ presence,฀ concentration,฀or฀variability฀of฀secondary฀ metabolites.฀The฀use฀of฀secondary฀chemistry฀to฀assist฀in฀host฀range฀predictions฀of฀ potential฀biological฀control฀agents฀is฀relatively฀unexplored;฀however,฀its฀relevance฀ is฀gaining฀recognition฀(Jordon-Thaden฀and฀ Louda฀ 2003;฀ Wheeler฀ 2005).฀ Like฀ many฀ plant฀groups,฀however,฀there฀is฀insufficient฀ detailed฀ information฀ available฀ describing฀ the฀secondary฀metabolites฀of฀D.฀bulbifera.฀ The฀steroid฀diosgenin฀occurs฀in฀the฀tubers฀ in฀the฀two฀North฀American฀species฀of฀the฀ genus฀(Martin฀1969)฀and฀several฀species฀in฀ southern฀Mexico฀(Morton฀1977).฀Tannins฀ and฀ polyphenolics฀ may฀ also฀ be฀ common฀ constituents฀in฀Dioscorea฀tubers,฀imparting฀ a฀ bitter฀ flavor฀ (Al-Shehbaz฀ and฀ Schubert฀ 1989).฀The฀ bitter฀ and฀ sometimes฀ poisonous฀components฀of฀D.฀bulbifera฀tubers฀and฀ bulbils฀ were฀ found฀ to฀ be฀ three฀ furanoid฀ norditerpenes฀(Telek฀et฀al.฀1974;฀Webster฀ et฀al.฀1984).฀The฀flavonols฀kaempferol฀and฀ quercetin฀were฀found฀in฀several฀Dioscorea฀ and฀ Rajania฀ species฀ (Williams฀ and฀ Harborne฀1988).฀Other฀Dioscorea฀species฀(e.g.,฀ D.฀ dumetorum)฀ contain฀ the฀ highly฀ toxic฀ alkaloids฀dioscorine฀and฀dihydrodioscorine฀ (Al-Shehbaz฀ and฀ Schubert฀ 1989;฀ Mabberley฀1997).฀Tuber฀extracts฀of฀D.฀hispida฀ Schlussel฀either฀containing฀these฀alkaloids฀ or฀ other฀ non-alkaloid฀ fractions฀ increased฀ mortality฀ when฀ fed฀ to฀ the฀ diamondback฀ moth฀Plutella฀xylastella฀(L.)฀(Lepidoptera:฀ Plutellidae;฀Banaag฀et฀al.฀1997,฀1998).฀Additional฀chemical฀analyses฀of฀this฀group฀are฀ needed฀ to฀ better฀ describe฀ the฀ secondary฀ metabolite฀ diversity฀ and฀ its฀ relevance฀ to฀ herbivory,฀particularly฀of฀the฀target฀weed฀D.฀ bulbifera฀and฀the฀sympatric฀or฀geographically฀proximate฀native฀Dioscorea฀species฀ in฀the฀region. Level of specificity needed by natural enemies The฀ family฀ Dioscoreaceae฀ is฀ poorly฀ represented฀ in฀ North฀ America,฀ but฀ more฀ abundant฀in฀the฀West฀Indies฀and฀Mexico.฀ To฀avoid฀use฀of฀native฀and฀economic฀species฀in฀North฀America,฀the฀West฀Indies,฀and฀ Mexico,฀a฀biological฀control฀agent฀should฀ be฀restricted฀to฀the฀section฀Opsophyton฀in฀ the฀genus฀Dioscorea.฀Typically,฀specialized฀ herbivores฀restrict฀their฀use฀of฀host฀plants฀ to฀a฀particular฀plant฀taxon,฀such฀as฀a฀genus,฀ tribe,฀or฀family฀(Ehrlich฀and฀Raven฀1964;฀ Mitter฀and฀Farrell฀1991).฀Although฀not฀very฀ closely฀related฀to฀D.฀bulbifera,฀species฀of฀ special฀concern฀are฀the฀two฀United฀States฀ and฀ Florida฀ natives,฀ D.฀ floridana฀ and฀ D.฀ villosa,฀both฀of฀which฀will฀be฀extensively฀ tested฀because฀they฀are฀sympatric฀with฀the฀ weed.฀Testing฀should฀include฀representatives฀ of฀ the฀ taxonomic฀ sections฀ to฀ which฀ Natural Areas Journal 275 the฀ geographically฀ proximate฀ northern฀ Mexican฀ and฀ West฀ Indian฀ Dioscorea฀ species฀ belong฀ (Table฀ 1).฀ This฀ is฀ section฀ Trigonobasis฀for฀the฀Mexican฀species฀and฀ sections฀Chondrocarpa,฀Lynchonostemon,฀ Dematostemon,฀and฀Rajania฀for฀the฀West฀ Indian฀ species.฀The฀ other฀ two฀ extant฀ Dioscorea฀species฀naturalized฀in฀the฀U.S.฀(D.฀ alata฀and฀D.฀polystachya)฀should฀be฀tested฀ to฀determine฀if฀the฀candidate฀enemy฀may฀ be฀potentially฀useful฀as฀control฀agents฀of฀ these฀species.฀Dioscorea฀species,฀including฀ several฀varieties฀grown฀for฀food฀in฀Cuba,฀ the฀ Bahamas,฀ and฀ elsewhere฀ in฀ the฀West฀ Indies,฀should฀be฀tested฀including฀several฀ varieties฀ of฀ D.฀ alata,฀ D.฀ cayenensis,฀ D.฀ cayenensis฀ subsp.฀ rotundata฀ (section฀ Enantiphyllum),฀ and฀ D.฀ trifida฀ (section฀ Macrogynodium),฀and฀D.฀esculenta฀(sect.฀ Combilium),฀although฀none฀are฀taxonomically฀close฀to฀the฀target฀weed฀(Wilkin฀et฀al.฀ 2005;฀L.฀Raz,฀unpubl.฀data).฀The฀testing฀of฀ these฀same฀Dioscorea฀food฀species฀will฀be฀ a฀priority฀if฀the฀candidate฀biocontrol฀agent฀ feeds฀on฀the฀tubers฀or฀bulbils. Areas surveyed for natural enemies Few฀ foreign฀ explorations฀ have฀ been฀ conducted฀ to฀ date฀ searching฀ for฀ natural฀ enemies฀ of฀ D.฀ bulbifera.฀ Some฀ surveys฀ have฀been฀made฀in฀Nepal฀by฀Pemberton฀and฀ Rayamaji฀(unpubl.฀data).฀Additionally,฀explorations฀for฀natural฀enemies฀have฀begun฀ in฀Ghana฀and฀Uganda,฀Africa฀(Overholt฀et฀ al.฀2003).฀The฀plant’s฀huge฀native฀area,฀both฀ tropical฀Africa฀and฀tropical฀Asia,฀represents฀ an฀impossibly฀large฀area฀to฀explore.฀Portions฀ of฀ these฀ enormous฀ regions฀ can฀ and฀ should฀be฀surveyed฀to฀discover฀a฀diversity฀ of฀ potential฀ control฀ agents.฀ The฀ amount฀ of฀ survey฀ needed฀ will฀ relate฀ to฀ project฀ development,฀ suitability,฀ and฀ success฀ of฀ released฀biological฀control฀agents. Natural enemies found On฀a฀recent฀survey฀in฀the฀Katmandu฀Valley฀ of฀Nepal,฀R.฀Pemberton฀and฀M.฀Rayamahji฀ discovered฀ several฀ highly฀ damaging฀ herbivore฀species฀on฀D.฀bulbifera.฀These฀include฀a฀species฀of฀Liliocerus฀(Coleoptera:฀ Chrysomelidae)฀found฀feeding฀on฀both฀the฀ leaves฀ and฀ the฀ bulbils฀ of฀ the฀ plant.฀ The฀ gregarious฀larvae฀defoliate฀the฀plants฀and฀ 276 Natural Areas Journal completely฀ consume฀ bulbils.฀ Specialists฀ are฀determining฀the฀precise฀identity฀of฀the฀ insects.฀Two฀ additional฀ chrysomelid฀ species฀Dactylispa฀brevispinosa฀Chapuis฀and฀ Lema฀sp.฀from฀Nepal฀may฀have฀potential.฀ Several฀other฀unidentified฀herbivores฀from฀ Nepal฀include฀a฀weevil,฀a฀leaf฀mining฀fly,฀ two฀caterpillar฀species฀–฀one฀skeletonizing฀ leaves,฀ the฀ other฀ feeding฀ on฀ leaves฀ and฀ the฀shoot฀tip฀–฀and฀an฀undetermined฀leaf฀ spot฀fungus.฀In฀Benin,฀Africa,฀exploratory฀ surveys฀ recovered฀ two฀ beetles,฀ Lilioceris฀ livida฀Dalman฀and฀Lema฀armata฀(F.)฀(W.฀ Overholt,฀University฀of฀Florida,฀Ft.฀Pierce,฀ pers.฀comm.).฀Intensive฀surveys฀should฀be฀ conducted฀for฀additional฀natural฀enemies฀of฀ this฀weed฀in฀other฀geographic฀areas. Several฀ insect฀ and฀ disease฀ pests฀ of฀ cultivated฀Dioscorea฀spp.฀are฀known฀(Tindall฀ 1993).฀These฀include฀yam฀pest฀species฀of฀ beetles฀ and฀ aphids฀ from฀ tropical฀ Africa.฀ The฀ cultivation฀ of฀ edible฀ varieties฀ of฀ D.฀ bulbifera฀in฀India฀and฀Africa฀has฀developed฀ insect฀species฀that฀are฀considered฀pests.฀In฀ West฀Africa,฀the฀pest฀list฀includes฀several฀ species฀ (Coursey฀ 1967;฀ Pursglove฀ 1972)฀ including฀Liliocerus฀impressa฀(Fabricius)฀ (=฀Crioceris฀impressa;฀Coleoptera:฀Chrysomelidae).฀This฀ species฀ has฀ been฀ reported฀ from฀ Nepal฀ (1524-3353฀ m฀ elevation;฀ as฀ C.฀ impressa;฀ Bryant฀ 1952;฀ Takizawa฀ 1989),฀Bangladesh฀(Das฀and฀Islam฀1984),฀ India฀(as฀Crioceris฀impressa;฀Sinba฀et฀al.฀ 1978),฀Malaysia,฀Burma,฀Sri฀Lanka฀(as฀C.฀ impressa;฀ Srivastava฀ and฀ Bhagat฀ 1967),฀ throughout฀ Southeast฀ Asia฀ (Kimoto฀ and฀ Gressitt฀ 1979),฀ and฀ China฀ (Yu฀ 1993).฀ This฀ may฀ be฀ the฀ Liliocerus฀ discovered฀ in฀Nepal฀by฀Pemberton฀and฀Rayamaji.฀In฀ India,฀ the฀ host฀ range฀ of฀ this฀ species฀ (C.฀ impressa)฀ may฀ include฀ additional฀ species,฀ namely฀ D.฀ alata,฀ Ficus฀ elastica฀ L.฀ (Moraceae),฀ Holarrhena฀ antidysentrica฀ Wall.฀ (Apocynaceae),฀ Callicarpa฀ macrophylla฀ Vahl.฀ (Verbenaceae),฀ unspiked฀ sandal฀(Srivastava฀and฀Bhagat฀1967),฀and฀ Cassia฀ sophera฀ (Fabaceae)฀ (Saha฀ 1973).฀ However,฀the฀genus฀Liliocerus฀is฀in฀need฀ of฀revision฀(E.C.฀Kane,฀A.S.฀Konstantinov฀ USDA/ARS/SEL,฀ Beltsville,฀ Maryland,฀ pers.฀ comm.).฀ Liliocerus฀ impressa฀ may฀ be฀ a฀ complex฀ of฀ species฀ with฀ different฀ host฀plants,฀perhaps฀with฀many฀Dioscorea฀ specialists.฀Preliminary฀adult฀feeding฀tests฀ of฀the฀Nepalese฀Liliocerus฀species฀suggest฀ that฀it฀is฀a฀Dioscorea฀specialist฀(Pemberton,฀ unpubl.฀ data).฀ The฀ diverse฀ and฀ complex฀ chemistry฀in฀the฀genus฀Dioscorea฀(Baker฀et฀ al.฀1966;฀Harborne฀and฀Williams฀1995)฀is฀ reason฀to฀believe฀that฀specialist฀herbivores฀ are฀likely฀to฀have฀evolved฀with฀D.฀bulbifera฀ and฀other฀Dioscorea฀species.฀Some฀newly฀ discovered฀agents฀in฀Nepal,฀or฀other฀yet฀to฀ be฀discovered฀specialists,฀may฀be฀suitable฀ biological฀control฀agents฀of฀the฀weed. Decision and recommendation summary D.฀bulbifera฀is฀currently฀a฀widespread฀environmental฀weed฀throughout฀many฀parts฀ of฀the฀southeastern฀United฀States฀where฀it฀ threatens฀the฀stability฀and฀biodiversity฀of฀ native฀communities.฀Control฀of฀the฀weed฀by฀ mechanical฀and฀chemical฀methods฀requires฀ repeated฀treatments฀over฀several฀years฀and฀ appears฀to฀be฀only฀marginally฀successful.฀ D.฀bulbifera฀is฀taxonomically฀isolated฀with฀ only฀two฀native฀congeneric฀species฀in฀North฀ America,฀ north฀ of฀ Mexico.฀ These฀ North฀ American฀congeners฀are฀assigned฀to฀different฀taxonomic฀sections฀than฀D.฀bulbifera.฀ Likewise,฀the฀West฀Indian฀Dioscorea฀and฀ northern฀Mexican฀species฀most฀proximate฀ to฀Texas฀also฀belong฀to฀different฀taxonomic฀ sections฀of฀the฀genus.฀Dioscorea฀alata฀and฀ other฀cultivated฀yams฀belong฀to฀different฀ sections฀ (Enantiophyllum,฀ Opsophyton,฀ and฀ Combilium)฀ as฀ well.฀ These฀ food฀ yams฀ are฀ grown฀ in฀ the฀ West฀ Indies,฀ but฀ have฀no฀commercial฀cultivation฀in฀Florida฀ and฀limited฀home฀cultivation.฀Herbivores฀ introduced฀for฀biological฀control฀of฀D.฀bulbifera฀must฀be฀host฀specific฀to฀the฀section฀ Opsophyton฀to฀avoid฀damage฀to฀desirable฀ plants฀in฀the฀region.฀Moreover,฀D.฀bulbifera฀ is฀geographically฀isolated฀from฀regions฀in฀ Mexico฀and฀the฀West฀Indies฀that฀have฀rich฀ Dioscorea฀flora.฀Potential฀candidates฀have฀ been฀ found฀ and฀ searches฀ for฀ additional฀ species฀are฀underway฀in฀Africa฀and฀Asia.฀ This฀ feasibility฀ assessment฀ suggests฀ that฀ targeting฀D.฀bulbifera฀for฀classical฀biological฀control฀has฀good฀potential. Feasibility฀ studies,฀ such฀ as฀ this฀ one฀ on฀ D.฀ bulbifera,฀ done฀ prior฀ to฀ or฀ early฀ in฀ a฀ biological฀ control฀ project฀ can฀ accurately฀ identify฀ risks฀ and฀ help฀ judge฀ the฀ suitability฀of฀the฀weed฀for฀biological฀control฀ Volume 27 (3), 2007 prior฀to฀significant฀research฀and฀monetary฀ investment.฀We฀recommend฀that฀feasibility฀ studies฀containing฀similar฀elements฀should฀ be฀done฀for฀all฀projects. ACKNOWLEDGMENTS This฀ work฀ would฀ not฀ have฀ been฀ possible฀ without฀ the฀ valuable฀ conversations฀ and฀ herbaria฀searches฀conducted฀by฀numerous฀ collaborators.฀ Previous฀ versions฀ of฀ this฀ document฀were฀improved฀by฀the฀helpful฀reviews฀provided฀by฀W.฀Overholt,฀University฀ of฀ Florida,฀ Ft฀ Pierce,฀ FL.฀We฀ thank฀ E.C.฀ Kane฀and฀A.฀S.฀Konstantinov,฀USDA/ARS/ SEL,฀Beltsville,฀MD,฀for฀determination฀of฀ Dioscorea฀herbivores;฀and฀for฀information฀ on฀the฀range฀of฀Dioscorea฀spp.฀O.฀Tellez,฀ Herbario฀Nacional฀de฀Mexico;฀B.L.฀Turner,฀ School฀Biological฀Sciences,฀and฀T.฀Wendt,฀ Curators,฀University฀of฀Texas,฀Austin,฀TX;฀ M.฀Reed,฀TAMU฀herbarium,฀Texas฀A&M,฀ College฀Station,฀TX;฀L.฀&฀R.฀Brown,฀SBSC฀ Herbarium,฀Houston,฀TX;฀G.฀Diggs,฀Austin฀ College,฀TX;฀A.฀Neill,฀Botanical฀Research฀ Institute฀ of฀ Texas,฀ TX;฀ J.฀Williams,฀ Sam฀ Houston฀State฀University,฀Huntsville,฀TX;฀ D.L.฀Gorchov,฀Miami฀University,฀Oxford,฀ OH;฀P.฀Howell,฀Broward฀County฀Parks฀&฀ Recreation,฀Ft฀Lauderdale,฀FL;฀A.฀Hunsberger,฀University฀of฀Florida/Miami-Dade฀ County฀Extension,฀FL;฀J.฀Vedaee,฀Broward฀ County฀Agriculture฀and฀Extension฀Education฀Davie,฀FL. Greg฀Wheeler฀studied฀for฀a฀PHD฀in฀Entomology฀at฀the฀University฀of฀Florida,฀graduating฀in฀1989.฀He฀has฀worked฀as฀a฀Research฀ Entomologist฀with฀the฀USDA-Agricultural฀ Research฀Service,฀Invasive฀Plant฀Research฀ Laboratory฀in฀Ft.฀Lauderdale,฀Florida,฀for฀ 13฀ years.฀ His฀ research฀ interests฀ include฀ biological฀ control,฀ the฀ chemical฀ ecology฀ of฀insect/plant฀interactions,฀and฀he฀leads฀ biological฀ control฀ projects฀ for฀ Brazilian฀ pepper,฀ Australian฀ pine,฀ hydrilla,฀ and฀ Chinese฀tallow. Robert฀ (Bob)฀ Pemberton฀ did฀ his฀ PhD฀ in฀ Entomology฀ at฀ the฀ University฀ of฀ California฀ Berkeley฀ in฀ 1980.฀ He฀ has฀ worked฀ as฀ a฀Research฀Entomologist฀with฀the฀USDAAgricultural฀Research฀Service฀laboratories฀ in฀ Berkeley,฀ Calif.,฀ Bozeman,฀ Mont.,฀ and฀ Volume 27 (3), 2007 Seoul,฀ South฀ Korea,฀ and฀ has฀ been฀ with฀ the฀ Invasive฀ Plant฀ Research฀ Laboratory฀ in฀ Ft.฀ Lauderdale,฀ Florida,฀ for฀ 13฀ years.฀ His฀research฀interests฀focus฀on฀the฀biological฀control฀and฀ecology฀of฀invasive฀plants฀ and฀insects.฀He฀currently฀leads฀projects฀on฀ biological฀control฀of฀Dioscorea฀bulbifera,฀ Lygodium฀ microphyllum,฀ Paederia฀ spp.,฀ the฀lobate฀lac฀scale฀insect฀(Paratachardina฀ lobata),฀ and฀ the฀ ecology฀ of฀ an฀ invasive฀ orchid฀bee฀Euglossa฀viridissima. Lauren฀ Raz฀ is฀ curator฀ of฀ the฀ Herbarium฀ at฀ Fairchild฀ Tropical฀ Botanic฀ Garden฀ in฀ Miami,฀Florida,฀where฀she฀has฀been฀working฀since฀August฀2004.฀She฀holds฀a฀PhD฀in฀ Biology฀ from฀ New฀York฀ University,฀ via฀ a฀ joint฀training฀program฀with฀The฀New฀York฀ Botanical฀Garden.฀Her฀research฀interests฀ include฀ systematics฀ of฀ the฀ yam฀ family,฀ Dioscoreaceae,฀ as฀ well฀ as฀ floristics฀ and฀ biogeography฀of฀the฀West฀Indies. LITERATURE CITED Adams,฀ C.D.฀ 1972.฀ Flowering฀ Plants฀ of฀ Jamaica.฀University฀of฀the฀West฀Indies,฀Mona,฀ Jamaica. Al-Shehbaz,฀I.A.,฀and฀B.G.฀Schubert.฀1989.฀The฀ Dioscoreaceae฀ in฀ the฀ southeastern฀ United฀ States.฀ Journal฀ of฀ the฀ Arnold฀ Arboretum฀ 70:57-95. Andres,฀L.A.฀1981.฀Conflicting฀interests฀and฀the฀ biological฀control฀of฀weeds.฀Pp.฀11-20฀in฀E.S.฀ Delfosse,฀ ed.,฀ Proceeding฀ V฀ International฀ Symposium฀ for฀ the฀ Biological฀ Control฀ of฀ Weeds,฀CSIRO,฀Melbourne,฀Australia. 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