INVASIVE ANTS: UNWANTED PARTNERS IN ANT-PLANT INTERACTIONS? (mm D,.,um., these examples a . -en ants and plants from ratine facultative, loose associations to s|tecies-s|)ecilic. ne ant can interact directly and mutualisms, and innumerable same obligate <|uciioii- e plant multiple ways. in lia\e been posed about the costs, benefits, and evo- benefit the plant in one interac- The lutionary implications of these relationship- plant in another. II. ,il ! ( tie. 1985; Bronslein, 1994; Jolivet, 1996). As in- net outcome for the plant will depend on the rela- vasive ants spread, their interactions with plants tive balance of a range of interactions, all of which arc inevitable and have potent iallv great implica- in turn will be influenced bv the same set of vari- ables that Ivpicallv iiilluence ant-planl interactions. know tent are ant-plant interactions altered by the intro- Itimately. vve will want to whether invasive I duction of these novel partners? the bala, ) Invasive ants possess a disbud combination ol enllv ] (Holway traits relative to native ants et ah. 2002). some In tins per. hypothesize ol the-e hail- p lli.il ;l I and provide a basis for predicting the outcome of these novel interactions. locus on the potential loi I the approximately 10.000 species of ants in ( >l differences between native and invasive ants the in the world, about >0 have been introduced around 1 . way they protect plant- from lierbivorv. tend llo- the world with the help humans; these may be ol moplera. and interlere with plant reproduction. termed exotic, or tramp ants (McGlynn. '>*>*>). In- These examples encompass more I the facultative. vasive ants are the small subset of introduced ant- are able establish and penetrate areas out- that to increasingly likclv to participate as they spread side of human-modified habitats (Holway el al., around the globe. 2002). Well-known examples in the United States \ltliough explore the dilTei ctiecs between na- I in' hide the red imported fire ant, Solenopsis invicta, i Symposia * pn.y helpful ii|e.| I New o Corson Hall. Ithaca. York 14853. i.S.A. Ijlt3@ K I y, \nn. Missouri Bot. Card. 91-108. 2003. 90: Garden Missouri Botanical The ami Hie genl inc anl. pilheim/ luimile. \ I.iiit lit- I tlc lire ant. Wasmaniiia aiiropiuielala. the big-head- ed Pheidole megacephala, and long-legged ant, anl. Anoplolepis gracilipes, also appear to be highly s |] I i See Table suniiuaiv of dish for a ibiilmti-. 1 One hallmark of invasive ants is their ability to become extremely abundant new then- habitats. in haps areas invaded by Solenopsis inricta I'illall in & WO). Lmepithema (Porter Savignano. humile I and megacephala (Hoi way, 1998). I'heidole (Hoff- man 1999) have shown the number et al.. all that workeis exceeds of invasive anl greallv thai of na- tive ants in nearby un-invaded areas. Several mechanisms are likelv eonl ribul ig lo invasive Mills" ii aehievemenl nf iiiunerieal Mipoiiorilv including es- cape from natural enemies and eompetilors and § * i f t 1 -r~ s changes eoloiiv -Inn hue Inward mil -ned. in -< |ii< -• 1 1 i niiilli-nesl sii|)ercoloiiies that lack inlra-peeiiic ag- gression (Holvvay 2002). et al., The physiology and behavior of invasive ants also likelv plav a role in llieir lenileucv lo achieve high abundance dom- (Holvvay et al.. 2(K)2). Kcologicallv inant arils, including invasive mils such as l.inepi- nil l*ji n ii II ill i i i | i i ; to take in more liquid foods, including Moral and and homopteran honevdew exlialloral ucclar isnei. ll The 1957: Davidson. 1998). ability to harvest these Mil oh re-oiuves mav be le.di lie-rich especiallv illl- ' 21 lempo porlanl in liieling ihe high aclivilv ol a large dvnamir den workforce, high ihereliv iiiainlairiitig a create nests the base of s tellite at ill & en lending phids (Kaakeh Duleher, o aggression another ligh level cliar- is non to invas ve ants and likelv enhances ss as predat rs(Holvvav el al.. 2(H)2). Ac- lydrale-rieh resources and a cause and force are hot the effeel of su- . II I 1 and compel dilative ilerfereuee mm abil- il i whirl, e anls and other eompetilors d. ..al splaeed (Hoi vay 2002). et al.. documented consequence of an invasive ant H ily oduction (Holway 2002). Linepithenm hu- el al.. for example, has displaced several species of '. ;aeic ants in California (Erickson, 1971; Ward. Human Holway, 1995; Gordon, 1996). 7; <S (Cammell Way 1996; :ugal et al., et al.. 1997). ^ & South Africa (Donnelly (iiliomee. 1985). mannia auropunelala has expanded I territory its how rich food affect they might protect plants from & May Australia (Majer, 1985; Heterick. plant reproduction. itats in Hoffman Vanderwoude 2000; ah. 1999; et ah, et ^minala 2000). Snlmopsis and other ants na- (¥.) W| R()TKrnoN H ERBIVORKS n{()M , |, become much the southern U.S. have less live to common & following iuva-ioii h\ .S. inrirlu (Porter Protection of plants from herbivores perhaps the is & Savignano, 1990; Cotelli Arnetl. 2000). As est recognized effect of ants on plants. long () | ( | and Invasive ants also affect other invertebrates ago as M) i. Chinese citn.s growers facilitated .„. x ; even vertebrates, usually negalivelv. \nopIolcpis r S ie ad of the yellow citrus ant, which preyed on p t |, blamed diminished populations of & gracilipes for is orange orchards (Huang Yang, 1(T )ivores i„ their | | K various invertebrates die Seychelles (Haines in p Sim e lelK < ahi|i|v ,„ prey on< or simp )!!7) . . ||1|s ,, i y Haines. 1978) and generating ecosystem-level is .. lss wou l-be herbivores has been noted in many [)a| ] ( changes through impact on the red land crab on & its svslems (Beattie. 1085: Holldobler Wilson, 1990). Christmas Island (Creen ah. 1900). Lim-pithnm, et rases p|an|s e an(s food or ,„ S()|nr ,. nti( . )V ()ffering _ | some humile associated with decreases insects is in ^^ „ one s|)(i||(i| . F()| . . x ., m[) ._ ;, s [h(m h[ that of {he ^-^ ( | ( ; California and llawah (Cole ah. 1992: Bolger in et ,„,. ,,„. pi ,. s( ,, ,. „,- extraflora nec . l ( The ah, 2000). great ,ed„c|,„u .-nd.-m.e „,- et in |;mr> mls protection js (( a(|ra( ., . jn ,. X( ., ia|lf ,t . f()r , Hawaii end 1800s sects lowland the the ,n at ol ^^ |mm m( |VS (Brnt 1977). ley, ir| ., , , ^ has been attributed to mvas.on In I'hrululr nu^u- ^^ ^ imasive ams ^ ^ ((f |rajls ass()< . ia(( , (1 „;,,, ^ (Zimmenn. ^ cephala * .wv u,r,rta has ,.„, v {q { worker and -i/e. high levels of aeli\ aggressive- ilv. nN. rd die southern in', i-i >-|» |. "-., 'iiai 'iia - in & s ness (Davidson McKey, 1995: Bronstein. 1998). Wasmannia United States (Holwav ah. 2002). au- el number workers ma\ large of verv active result \ ropuiictdta has eliminated or reduced terrestrial in- in increased plant visitation b\ ants leading to de- Calapago- vertebrate populalions the l-land- in (Caume creased herbivory ah. 1997: Bronstein. et New (Lubin, 1984) and Caledonia (Jourdan. 1997). Caume 1008,: et ah. 1998; Uinsenniair et ah. 2001) The mechanisms lor these effects are not always because herbivores are located more rapidly and some combination clear but likelv in\ol\e of prc- have shorter residence time on the plant (I)uarte a & "'" Kocha Codov Hergallo. 1992). Benefits the to J'"" some plant probably level off or even decline at An colony however. extremely large colony size, \M) Ol k.omi-.s <>l niav imposr a on the plant the ants are steal- . ()S if ( , KACIIONS ing nectar, tending Homoptera, interfering floral enemies ,ialmal herbivores, or excavat- vvilh ,lu ° f established that the na- ' ng system. Kesearch determine the plant's root to dependent on ture of ant-plant interactions is l vhere the cost-benefit trade-offs lie with respect to variables including ant behavior, ant colonv and stage, host plant attributes, ami the abundance iinl ,ol,,n > si/t ' ,1;,s > el to 1m* (l(>l \ggressive behav ior also aids behavior other organisms the svslem an.) ol in ph»» herbivores (Fiala ah, 1989; Letour- '"»»' et Cash- (Buckley, 1982; Beattie. 1985; Keeler. 1080; man, 1991; Davidson & McKey. 1905: Bronstein. '"'an. 1985: Bronstein, 1998). Bentley (1977) re- laled ant aggression on plants to three factors: pred- 100 1998: Jolivel. 1096). As explained above, in- 1, "lory hehav ownership behavior or the defense vasive ants tend have larger colonies and exhibit ior. to and swarming Mo boundaries (Way. 1965), moie aggressive behavior than nativ e ants. erritorial over, invasive ants appear to have a stronger lavior or the ability to rapidly recruit workers, p may enhanced many three behaviors be at the colony dilection than native ants for .!. ,', ,!, Aggression resources, which are invariably obtained directly I bv having a large workforce. is imlirectlv from plants. Since native ants are negatively correlated with proximity to an ants' f i <|uenllv displaced when invasive ants enter a n disturbance near an ants" nest or food source I: habilal. will be liail- ol the invad ers that inl elicit a stronger response than a threat en- it I The away ence outcomes \ppl\ing nlered farther (Way, 1965). vagile, po- future for the plants. . may isting models ol ant plant inleiacho•ns, (level oii ion- ne^ling bebav ioi ol invasive ants al- 1 them hypotheses about how invasive ants' levaled abi to nest In closer proximity than a native < equatu the side of the :ice, left greater henelit margin for the plant whei ants are present. side of the e ;ft Ant tending honeydew-producing of 1 •luding scale, mealybugs, apbids. & (Way. 1963; Carroll Jan/cn. 073; l!„eklev. I & & Holldobler Wilson. 1990; Davidson 198,7: ant would, possibly facilitating a grcalci a^uressive Vie key. l00.- Homoptera extract phloem from the {). host plants and excrete as honeydew. Ants feed- it Some ants provide protection from herbivores ing on the honeydew ollen protect llomoplera die-,,- while coll. -cting extrafloral nectar. Keeler (1981: from parasites and predators (Wav. 1903: liuckley. 190) modi-led the conditions under which the mu- 1987). The ant-Hon.optera mutualism may be det- tualism is favored: rimental lor the plant, robbing phloem and of it sometimes leading mold accumulation (Bach, to - D)H]>I. [A(1 P 1991; Lewis 1976) or phytopathogen et al.. trans- = where p probability that ants will find the plant. mission (e.g.. pineapple mealybug disease will = = A effectiveness of ant-defense. I) effectiveness (Ueardslev et al.. 1982). I'hylophlhora pod rot - & of other defense*. intensity of herbivorv. and (Fvans. 1973). swollen shoot virus (Taylor Ade- II dovin. 1078)) while conleriing no benefits ex- in plants' perspective, the miitualisi change (Ih.ckley. 1987). Less commo.dy. the inter- when may the left side of the equation, the benefits to action benefit the plant ants deter other if & the plant, exceeds the right side, the costs of at- herbivores while lending Homoptera (Carroll A & tracting the ants (Keeler. 1981). schematic of the Jan/en. 1973; Messina. 1981: Compton Robert- shown relationship in Figure son. 1988). is 1. Given the numerical superiority, attraction to As with plant protection from herbivores, the common carbohydrate resources, and aggressive character of characters to many invasive ants will af- > we invasive ants, might expect that fect their Homoptera-lending abilities and conse- p mlm MVi p, , . , > A an( A„„ m Since I) is primarily a factor quently the outcome for the plant. The need for l imilM „. .. of the plarrt and the hcibivore(s). and I) carbohydrate resources and ability to harvest co- I „. ) are not likely to differ. ll may exceed H„„ if pious amount- o| liquid provides the basis for the im( . K , 1W . inlraguild puliation i- a factor, i.e.. ants prev on allraetion ol iuva.-ive ant- |o llomoplera. \nl ag- il or inlerlere with the natural enemies of herbivores gression, particularly ownership behavior, an is ef- (Fubanks. 2001). However. may be less than II , H„, if invasive ants diminish herbivore popula- pre<lators of Homoptera (Wav. 1963). I'olydomy and lu , tions via direct or indirect interactions that affect nest vagililv may allow invasive ants to reside in herbivore eggs, larvae, pupae, or adults away from elo-er proximity these carbohydrate resources to than would native ants. dueible defense (Koptur. 198,9: Ness. 2001) will Ant abundance, however, may be the primary I, H increase with H. For example, greater affecting inva if is trail H than then extradotal nectaries be may will in- as affect im ,. (W . it mechanisms. Higher numbers may aut Iraiislali be will greater thai into a higher probability locating the tendees. ol C Homoptera h nils a byproduct mutualism with the plant (2a) and when iii it ws indicates the direction of the effect and the positive and the arrow indicates the strength of the .•Keel. Dotted lines f Homoptera, and arc as defined Figure In 2a, II. \. I) in 1. doler herl.iv.ire> mi the plant hears the cost of hosting the h> and a higher ant homopteran ratio may make ants eeplibilily to phylopalhogens. Other lerms remain : = enemies inure effective at deterring their partners" the same: p probability thai ants will find the = A (Sleyn. 1955). Tending ants are a limiting resource plant, eflecli\i-nes> nl aiil-.l.Ten-e against = honevdew-producing Homoptera many to in sys- luoii-homopleran) herbivores. effectiveness of I) & Cushman = tems (Addicott. 197K: Sudd. 1987: Ad- oilier defenses. intensity of (non-homopteran) II & dieott, 1989: Breton Addicott. 1992: Fischer et herbivory. Considering ihe niva-ive ants trail- ol 2001). and well-tended Homoptera may grow homopteran al.. favor high populations, prob- that is it reproduce more and produce more faster, rapidly, able thai in main cases C,,.,,,^,,,. will be great. -r ihan young than unten.led ones (Way. 1963: Brislow. The probability that the ant finds ihe plant, Ci,-„ .,„- a Where Homoptera 1984; Morales, 2000). the ant may abundance vary not only with the of the ant. : [t. becomes Homoptera may become ratio loo low. ant Homoptera |M.s-il>l\ will: the ability of different lnil prey or be more easily parasitized or preyed upon & to recruit ants (Del-Claro Oliveira. 1996). It is by natural enemies (Way. 1963. and references unclear, though, whether in\a-i\c ant- may ie-p.>ml & Breton Addicott. 1992: Sakata. 1991: therein: Hy- attraetanl en.- differently than native ants. to The superabundance achieved Jolivel. ( by I') )()|. pothesized differences and for native in \. ». I 1 1 invasive ants may keep the tender: tendee ratio from below din -hold. such a case, falling — In 1 1 1 1 with the lood-lor-prolection mutualism involving we would expect limits the abundance of both to mulualists he imposed by the host plant. to only be niainlained ihe benefits, in terms of de- if may depend Impacts on the plant. however, also terred lioinopl. herbivores denoted on the iioii ijti Homoptera on whether the ants tending deter other side of the equation, exceed the costs exacted left hn. herbivores. byproduct mutualism 2<M)| In this . Homoptera. on the plant by the the right side of the plant benefits indirectly from the ants' pres- exceed the equation (Fig. 2a). If costs to the plant Homoptera from hosted ence; the ants benefit the by the plant and possibly the herbivores, they are if toward a parasitic relationship with host (Fig. its Homoptera captured as prey. In this scenario. arc 2b). possibly resulting in reduced fitness of the mod- analogous extralloral nectaries and Keeler's to change detect any plant plant. Stu.li.-s that to in l.iil can be modified (1981) as: el Homoptera fitness with outbreaks associated with - > D)H C p[A(l J h , side of the equation (formerly the iu- it Seed predalion and Impacts Inn-resting. ants of on disposal and seed prcdation have received Seed Willi few exceptions Yam.. 1994: s, '«' (1 set. (e.g.. »"»"" attention than impacts on seed myr- commonly set. In Puterbaugh, 1998). ants have been re- mecochoroiis muliialisiiis. ants disperse seeds away garded as unwanted guests flowers (Kerncr. in Imm lh "' ollen burying them their IH78: Buckley. P>f!2). Attracted In floral nectar. <- P 11 1 " P"«»'l- in eliaosome ants mav damage floral structures, and depress pol- nvs[. '" «'xclinnge lor the lipid-rich al- belied m«,I (Buckley. 1082; to llie Beattie. 1985). ien viability with their antibiotic secretions (Kerncr. aL be di>per»ed -eed- iherelore mav ex-ape compe- 18)78: Peakall 1991: (ialen. |000|. \> with el I Homoptera and extrafloral neetaiy lending, super- titi() " W1, siblings and parents and are less sus- '> abundanee and an <<'I>lible to picdalion and other threats, such as fire affinity •< -arboh\<lrale resourc- I'm may es combined with levels agression would (bu.kley. 1082: Beattie. 1985). Ants also be lii-h ..I' see(l harvesters, consuming the seed Seed lead to the expectation that invasive ants would be itself. members harvesters, however, do not eat the seeds they exceptional recruiting colony flowers all at to and mav and collect, therefore act as accidental seed exploiting nectar. floral & numerous dispersers (Buckley, 1982: Holldobler Wilson, aggressive ants are present inflow- If 1990). presence may ers. their affect other floral visitors. may Various species of ants may be attracted toeliao- Pollinators be forced reposition frequently to somes and opportuuislicalK lake myrme- to avoid attack by the ants, and this mav result part in in mutualisms, whereas I'ocliorous harvester ants tend increased transfer of pollen and consequently high- special adaptations harvesting, consum- er seed set. Alternatively, pollinators mav avoid the "> ll; '\<- for m & «»"• storing se, -,b loll.lohler Wilson, 1990; flower altogether, or reposition too superficially for ^- 1 1 Keeler. 1989). In both cases, the ants need effective pollen transfer, ultimately resulting in de- to (a) creased seed \' <bseover the seed. recogni/e the seed as a re- set (Wyatt. 1980). plethora of (!>) floral source, and be abb- carry the seed back antagonists, including pollen consumers, and other (c) to to florivores, however, may also be deterred, perhaps tlie "<*st. s<^ (l discovery will be dictated by ant The ants" ultimate impacts on seed be between ant activity and seed availability, and the set will dependent on and attractiveness of the eliaosome. present (Beattie, the attraction availability of if floral nectar in the context of the ants' seasonal diet pref- 1985; Keeler. 1989). Seeds are typically high in and erences. activity patterns, and abundance, the lipids proteins: recognition of the seed as a iiuin- desirable resource may depend on ber of pollinators and antagonists and the relative floral their abundance susceptibility ant deterrence, structure and and composition of other food sources to floral m defenses against ants, and pollination require- the environment and the dietary requirements of llie when merits of the plant (Kerncr, 1878; Koptur. 1979; the colony the seeds are available (Beattie. & K my Vinson (ireenberg. 1980: Huxley 1991; 1985). In every rinecochorous system studied, Culler. & aL Klinkhamer de Jong. 1003; an/a 1905; seed-dispersing ants comprise only a small subset el I, & Koptur Timing. 1008: Pulerbaugh. 1008,), as well the .ml specie* present, and then behavior to- <>l ns the relative difference between ants" on ward seeds can vary from one day to the next (Beat- (-fleets polhnators and Moral antagonists. Kor example. tie. 1085). suggesting thai recognition of the seed I would expect nectar-robbing by invasive ants as a valuable food resource not constant among to is have little effect on seed sel across a plant popu- anl species or oyer time for a single species. The tition for the resource, e.g.. if nectar is available in pend on llie ants" foraging behavior and size and demand excess of by pollinators. would expect shape complementarity between seed and Kec- ant I ( invasive ants to be more likely to decrease seed set lei. 1080). Harvester ants must also have the man- in a plant species that has few Moral anlagonisls dibular strength and agililv to ingest the seeds and is dependent on a few species of small polli- (Beattie. 1085). How nators, than in a species that sutlers from many do we expect invasive ants compare to to antagonists and has diverse floral a pollinator guild. native ants in these requirements? Traits of invasive Moreover. Mowers which in nectaries are in close ants that have formed the basis lor hypotheses proximity the stigma and anthers to relative to t paper. namely elevated lance, aggn-ssiou. and ical or physical defenses against .nils. \\ helhei dif- a!>uii( much attraction to carbohvdrali ma\ not have as •>. on seed predalion and dispersal. \iimer- ance to phytotoxins, for example, will enabl infliicm -e superiority of invasive ants may increase the certain groups of anls to evade these defenses it-al i However, discover seeds. probability they will llial common of invasive ants oiler capacity trails little lor predicting liou invasive anls will respond to the ml therefore might lack specific ( may Other be seeds encounter. that traits tliev may linked seed discovery and dispersal not vary to imidn mcphala are lenopsis at- Inn. Tisriv; I.vnt tracted to oilv. lipid-rich lood sources (Vinson cK I'l <)\ • : i Greenberg. 1986; Sanders 1992). and seed et al.. Do observations asive ant-planl iulerac- & harvesters occur both genera (Holldobler Wil- in comhi- tions support pred that the distinct Tims, we might expect these invaders son. 1990). outcome the will affect s some and even have the to be attracted to seeds, of be- interactions with plants? Specifically, r mandibular adaptations helpful for ingesting -rnls. of their combination of trails, are invasive more but perhaps no so than native ants. lore likely than native anls to deter herbi- teud llomoplera the detriment of host to There and with plant reproduction? interfere >een few direct tests. Most research on ant been done with herbivores has in :tions noted above, numerical superiority, aggn-s- how popula- n pest behavi crop yields are affected by changes in ant 1 account differences likely to for all ml has not explored any particular aril at- ributes influencing the interactions. Still less is may vary t s ants affect seed set, pre- i among ants, hut an- unlikely to vary consistently Nonetheless, examples below ersal. among invasive and native ants such as tempera- vidence of the importance of the ture tolerance, daily activity patterns, colony cy- cles, and seasonal preferences for food types will and scoring the influence of ant biology the Kven certainly affect ants" relationships with plants. other organisms in the system in determin single ant species, associations with plants for a outcome of these interactions lor the plant. may change spatially or temporally. For example, the derive plant protection largely linked to ol is which mav change depending ant foraging patterns, examples on the nutritional requirements of the colony (e.g.. ol of invasive ; and reproductive cycles), the avail- in relation to .... resources ah. hvi ofein that ability ol require less foraging effort than those on the plant & & (AM Reagan. 1985: Vinson Green- rarely do they pinpoint any particular characteristic of interest & Rapp Salum. responsible effects on herbivores. berg, 1986; Stein et al., 1990; ol the ant for & Some which can be gained from cases 1995; Cornelius Crave, 1997). insights in lor example. Attributes of the potential prey items. flomop- the invader fails to deter herbivores, tera, and the host plant will also play roles in de- Anoplolcpis gracilipes affords protection from the fining ant interactions with these organisms (Way. -licking bug. 1,., '.'-' < Inn. i). in Sol- & omon coconut when reaches high abun- 1963; Cushman, 1991; Huxley Cutler. 1991; Islands it when abundant on Bronstein. 1991). and invasive and native ants mav dance in the trees. But prey are diverge their responses to these variables as the ground. A. gracilipes fails to forage in the trees in Many herbivores (Van Per Coot. 1916; kaak- and premature null. ensues due to A. cocophaga well. ill & eh Dutcher, 1992; Pavis 1992: Cunawar- damage (Creenslade, 1971). In Keeler's (1981) et al., & & dena Bandumalhie. 1993; Cornelius Rernays. terms, in this case a high A, ability to deter her- 1995; Montgomery heeler. 2000: Brinkman et bivores, is incou ii H In tin c\ \\ I I i, i , I i ii il & 2001) and flowers (Kerner. 1878; Willmer aging on the plant is low. al.. (p) chem- Stone. 1997; Gha/oul. 2090) have effective reducing the herbivore attack on the : other natural cnt(ili>ti< > ries are induced by Several studies have shown that different invasive inva lative ant's interactions with the her ants are attracted to \( ;tlh»i ne. lar and can de- and specific the invader ;il ol . i till*-—, lliat ; i 1 1 1 i J crease herbivory on extrafloral nectar-hearing are Holway plants (see 2002. The et al.. for a review). of extrafloral nectar an is ir high population density of Plwidole mrgarcphala system; nectar extrafloral r and tending of extrafloral nectaries are hlamed response its to herbivory, therel for the difference populations of shrnhs between and wasps in parasitic (Mess megacephala and P. native ant-inhabited sites ments have shown in that .S. i Australian The Vrena rainforest. native lobata anls and preys on wasps L. the parasitic c and the introduced Senna nblnsi/alia H. (I,) S. Il- Ceratoma catalpae (Hoisdm little lioni lolivory in area-- invaded by /' megace- phala. whereas in areas with native ants, the shrubs k.lv ,\ are small, isolated, and heaviK attacked bv herbi- nectar production coinciding will) the stage of col- vores (Hoffman et al.. WO). Other studies dem- ony cycle when workers prefer protein-rich resourc- I & onstrate that Salenapsis inricla (Fleet Young. es. So/rnnp^is inn, la i- apparently as effective a 2000). I.inepithema hnmite (Koptur. and 1070). predator of C. catalpae as are the native ants be- Wasmaiuaa 00 (iiimpmn -lala (Meier. I) also are al- cause preys on pupae and pre-pupal iiislars as 1 it well as larvae, and because of exceptional ag- its inlroduced sometimes habilal-. to the benefit of the gressiveness when prey are encountered. Thus, plant. Kill these studies, as with most, do not com- while S. inricla disrupts the mutualism by pre- pare the behavior of invasive ants to that of native do nor explore ants, they specific attributes of in- visiting extrafloral and protecting Catalpa i vasive- ants that may be influencing the interaction creased herbivory (Ness. 2001). Research exploring the interact ions of Sol, /, apsis Pulling the example in the c inricla with Catalpa hignanioides Waller provides (1981) model (Fig. even with 3), These der versus herbivore deterrent. studies reveal both types of outcomes outlined above occur, that which ant-Homoptera mutualism those in the is para-ilic Inward the plant and those in which the mu- ants lending llomopleia enter into a byproduct ml deterring iion-homopteran load tualism with the pi. l.v be herbivores. will 1 , Linepilhema humile^ abundance, aggression, The difference 1 duced herbivory and the investment in extradural and tending of aphid* have all been related to its ability to control populations of the pine p reces- & moth (Tlianmrlopoea pilvorampa Den. present than when native ants are present. sionary (Way Porluual pine plantations ah. worth noting that the probahditv ol lo- Schiff.) in et p. is It L on may he inlluenced 1999). The aphids attract foraging humile to pine cating loraging the plant, an- 1 crowns, baler the season, pine pioce-.-donarv tree in As such, an moth larvae on lives with humile are fiercely sard offered. t /.. may attacked, whereas those on native ant-occupied Solenopsis inrirla plantations lives are ignored. oiiseqiienllv. parts of ( humile escape severe abundance are inhabited by the Indeed, high of thai 1982). S. /,. ir, pilvnoimpa been offered as an explanation for the la defoliation caus.-d by '/.' in native ant- frequency between nec- iuhahiled areas, figures la and b contrast the in- difference foraging in its (Agnew taried and nectariless isolines of cotton et ah. 1982). Analogously, is possible that high den- /.. humile are present in terms of Keelers (1981) it invaded Cutalpa bignonioi- mo<hlied model derived above. the of inrictu in sity S. des stand (Ness. 2001) facilitated the ants" foraging on the plant, notwithstanding the absence of its at- moptera in cacao (Theobroma cacao L.) is a study traction to extradotal nectar. In these cases, if abi- in contrasts, and illustrates the pos>ibilil\ lor dif- same outcomes occur between the plant diminished otic or other conditions ever result in ferent to Wasmannia auropunrlala may become and West abundance the invader ant. In Africa. of S. inrirla. spread among cacao plantations because deterring herbivores than ants that actively less effective at is deters pestiferous mi bugs despite may not be as abundant, but are lured to the plants effectively rid it and association with high levels of scale psvllids its (Knlwistle. 1972). In contrast, in its native Brazil. mealybug Planororrus auropunrlala tends the If. mans Homoptera cacao and other all (bissol in i Lincpilbcma hum Phei- and control p.-| herbivores possibly be- \noplnlepis grarilipes. He. fails to dominance and Wasmannia auropunrlala cause does not always achieve in the mcaiK-cphtilit. flulr it De Souza have been noted for their ability to cause Ho- ant mosaic (De Medeiros et ah. 1905: et all moplera outbreaks various parts of the world ah. 1998). In the parlance of the modified keeler in C may some- (1081) model, West Africa. the cost to the (Holway ah. 2002). Solenopsis inrirla in et . h llomopleia associated with times obtain carbohydrates directly from plant tis- plant of hosting the 11. sue (Vander Meer ah. 1905). but also has been auropunrlala. is outweighed by the high A. the et associated with increased llomopleia populations ability of W. auropunctata to deter key herbivores, smd (lofgren. 1980; Holway ah. 2002). The data col- and the ant can be to have entered a In product el auropiinr- these studies often discern any par- mutualism with cacao, but in Brazil. U. lected to in fail lala lending rim imposes a high and a small /'. (.],, exceeds Homoptera outbreaks. While some resulting in a cost to the plant that the responsible for \. aggro- abundance, evidence of the importance of benefit. megacephalu Simla! Pheidole native in its Iv. mealybugs. Planororrus West Africa tends the ritri my and which arc associated with examples below, evaluation of prediction that njalensis (l.aing). I', these common invasive aul hails play a major role swollen shoot virus in cacao (Taylor Adedoyin. v\. determining interactions with plants will be 1978; Campbell, 1994). As part of its tending be- their in enhanced by further detailed study. However, soun- havior. P. megarephala transports soil from the homoplerans ground to create tent shelters for the Plnlopluho- and thereby acts as vertical vector of a anship and (4a) the Immile-T. Linc/iilliciuii |Hll,). Tlie.h.eetioiMil ll indicates the direction of the effect and the positive row indicates the strength of the Doited effect. lines and igures 2. In la, the native ant nol attracted is I Vl "l>l"'k liiils vy on the major herhi '"> "i "Umk illustrates inulnaliMii betueeii humilv II) ili« >|-.mIii.-| aral the pine I I .\ /.. | Nr to the lives aphids and preys on l>\ /.' pi/rotam/,,, to the Ixtutit of the plant. Mark ra spores, eliologie agent of pod llie mutualism rot benefits ihe plant (Kvans, 197:5). In this ease, comprises not only C,, the introduced range. this If the direct cost of hosting the mealybugs. also uld expect studies (hat that • I 1 1 1 associated increased bene Id.' likelihood of in fee I ed with two of the worst diseases of cacao. While effects of the ants no cacao studies have ever reported relationships a. a bl- -. i-l< between mrgarrphala and homopleraii \\ m,,m her- Hut this not is t bivores, it is unlikely that strong deterrence of her- fitness is noted, is usually reported as decreasing il bivores (a high A) would have gone unnoticed by (Beallie, 1985; Holway 2002). suggesting et al.. that farmers aware intimately of any effect on their hi most r.ivrs ih, invasi\c nil Imnoptera mutual- I Phcldolc megaceplmlus yields. fre(|uenl association ism is parasitic for host plant, beatlie (1085) its Homoptera with high outbreaks the detriment to of further points out that the vast majority of data de- plunt places Illness firmly in the pest category damage it in sciilini'j ;in to plants from lii iii 1. )l« -I is 1| & West Africa (Taylor Adedoyin, 1978). agroeeosyslems. or other heavily manipulated cn- between interaction lomoplera. cacao, and \noplo of Homoptera may be depauperate. Discern- I (jiiile Papua New The lepis gracilipcs in Cuiiieu. ant re- ing whether there are differences how the inva- in sive ant-Hoinoplera mutualism affects plants the in abundance its (baker. 1972). displaces the native It ultural versus less manipulated environments rii is (Room black pod Smith. 1975; McGregor rot cv ei dilioiial research. Moxon, Way & 1985; Khoo. 1992). Moreover, un- like the ants displaces. ;nu hnia-ses it 1. L ilipr*. cocoa weevils and a<lult persistently disrupts egg and laying foraging of several and inirid eoreid bugs, all of which are major pests (Knlvvistle, 1972; with exlrafloral nectaries and Homoptera. the McGregor & Moxon. Way 1985; Khoo. 1992). cK same but the ant fails to forage in trees in Malay- set. seed dispersal, and seed predalion precludes cacao and sian so is not effective against herbivores attempts to lest the predictions outlined above at (Wax khoo. ,\ I , ),'!, )|. indicating that a low p, prob- present. A brief review of the current slate of ability of finding and lorat-.iirj mi the plant, can knowledge can. however, point early trends and to ibility to deter its herbivores. identify areas lor future research. examples above ie suggest that ant-llomoptera Although several species of invasive ants have lalisms that are parasitic on the host plant are been observed to forage in various (lowers (Adams. occur likely to in the invaders' native range. I'>8(.: I.olgrei,. 1080: Bins. 1000; Hara K llata.