arthropod surveys on palmyra atoll, line islands, and ... · 485 arthropod surveys on palmyra...

485

Arthropod Surveys on Palmyra Atoll, Line Islands, and Insightsinto the Decline of the Native Tree Pisonia grandis (Nyctaginaceae)1

Alex T. Handler,2,3,7 Daniel S. Gruner,3,4 William P. Haines,5 Matthew W. Lange,6

and Kenneth Y. Kaneshiro3

Abstract: Palmyra Atoll, in the Line Islands of the equatorial Pacific, supportsone of the largest remaining native stands of Pisonia grandis forest in the tropicalPacific Ocean. In 2003, we surveyed terrestrial arthropods to document extantnative and introduced species richness, compare these lists with historical rec-ords, and assess potential threats to native species and ecosystem integrity. Intotal, 115 arthropod taxa were collected, bringing the total number of taxa re-corded since 1913 to 162. Few native species were collected; most taxa were ac-cidental introductions also recorded from the Hawaiian Islands, the presumedmain source of introductions to Palmyra. The overlap with previous historicalsurveys in 1913 and 1948 was low (<40%), and new species continue to estab-lish, with one species of whitefly reaching pest status between 2003 and 2005.We observed numerous dead or dying large Pisonia grandis, and the green scalePulvinaria urbicola (Coccidae) was particularly abundant on trees of poor health.Abundant introduced ants, particularly Pheidole megacephala, tended this and otherhemipterans feeding on both native and introduced plants. We hypothesize thatthe Pheidole-Pulvinaria facultative mutualism is causing the decline of Pisoniagrandis. Because of the unique properties of Pisonia grandis forest on oceanicatolls, its importance for nesting seabirds, and its alarming global decline, im-mediate conservation efforts should be directed at controlling introduced Hemip-tera and disrupting their mutualisms with nonnative ants on Palmyra Atoll.

As biogeographic barriers break down inthe face of increasing global commerce and

travel, introduced species have become adominant component of global environmen-tal change (Vitousek et al. 1999, Mack et al.2000). Oceanic islands are among the systemsmost vulnerable to biological invasion andhomogenization (D’Antonio and Dudley1995, Cowie 2001). Their small size allowscoexistence of fewer total species in smallpopulations relative to continents, and theirnative biota evolved in geographic isolationfrom many functional forms of predationand competition (Carlquist 1974, Wilson1996, Whittaker 1998). Although the replace-ment of endemic species by introducedspecies may actually increase local speciesand functional diversity on islands (Sax andGaines 2003), regional homogenization ofbiotic communities causes decline in totalglobal diversity (Samways 1999, Olden et al.2004).

Palmyra is a remote atoll in the northernLine Islands (Figure 1), approximately 2,000km south-southwest of the Hawaiian Ar-

Pacific Science (2007), vol. 61, no. 4:485–502: 2007 by University of Hawai‘i PressAll rights reserved

1 Funding for this work was provided by NSF GK-12Grant no. DGE02-32016 and the U.S. Fish and WildlifeService. This is contribution no. 2368, Bodega MarineLaboratory, University of California at Davis, Davis, Cal-ifornia. Manuscript accepted 7 January 2007.

2 Corresponding author: [email protected] Center for Conservation Research and Training,

University of Hawai‘i at Manoa, Honolulu, Hawai‘i96822.

4 Bodega Marine Laboratory, University of Californiaat Davis, Bodega Bay, California 94923.

5 Department of Plant and Environmental ProtectionSciences, University of Hawai‘i at Manoa, Honolulu, Ha-wai‘i 96822.

6 The Nature Conservancy, Palmyra Atoll NationalWildlife Refuge.

7 PowerPlants Hawaii LLC, Honolulu, Hawai‘i96816.

chipelago (5� 53 0 6 00 N, 162� 6 0 11 00 W ). Theatoll consists of roughly 50 small, low islets,with a total land area of less than 5 km2 anda maximum elevation of 2 m, all surroundedby a barrier reef. With an average annualrainfall of more than 4 m, Palmyra is a wetatoll within the Inter-tropical ConvergenceZone (Mueller-Dombois and Fosberg 1998).This high rainfall, coupled with huge nutrientinflux in the form of guano from thousandsof resident seabirds and migratory shorebirds,supports thickly vegetated rain forest that isunique even in comparison with nearby,more arid islands such as Kiritimati (Wester1985). The atoll is home to a relatively intactand diverse marine ecosystem; 29 species ofbirds; the coconut crab (Birgus latro L.), theworld’s largest terrestrial arthropod (Reyne1939, Chauvet and Kadiri-Jan 1999); and

rare stands of Pisonia grandis R. Br. (Nyctagi-naceae). Many of these native species arelisted as threatened or endangered becauseof historical human exploitation and habitatdisturbance throughout their ranges and con-tinued impacts of introduced species (IUCN2004).

Palmyra probably did not support persis-tent populations of indigenous peoples,although there is evidence of sporadic Poly-nesian occupation (Dawson 1959, Wester1985). However, in the brief 200-yr historysince European seafarers stumbled upon it,intense human disturbance has severely im-pacted the atoll (Dawson 1959). Fanning firstsighted the atoll in 1798, but it was namedwhen an American ship, The Palmyra, driftedonto its shores after a storm on 7 November1802. In 1862, Kamehameha IV claimed Pal-

Figure 1. Palmyra Atoll, northern Line Islands, equatorial Pacific Ocean.

486 PACIFIC SCIENCE . October 2007

myra as part of the Hawaiian Kingdom. Pal-myra Atoll was recognized in turn as a U.S.territory with the annexation of Hawai‘i in1898. The atoll passed variously throughpublic and private ownership until 2001, in-cluding a period of intense military occupa-tion from 1938 to 1961. During that period,the U.S. Navy dredged lagoons and builtbunkers, recreation centers, an airstrip, a hos-pital, and causeways connecting islets. Duringpeak occupancy, the 182 ha of land area sup-ported over 6,000 naval personnel and sub-stantial infrastructure (Dawson 1959, Anon.1998). In 2001, Palmyra Atoll was designateda National Wildlife Refuge of the U.S. Fishand Wildlife Service. Currently, PalmyraAtoll is jointly owned and managed by TheNature Conservancy and the U.S. Fish andWildlife Service (Anon. 1998) and is unin-habited except for a small cadre of scientists,resource managers, and transient crew.

The hallmark indigenous plant species ofthe atoll is Pisonia grandis, which grows toheights often exceeding 30 m in dense mono-dominant stands in some of the largest tractsremaining on tropical Pacific islands (Walker1991a, Mueller-Dombois and Fosberg 1998).With sticky fruits dispersed by seabirds (AiryShaw 1952, Burger 2005), P. grandis forestsare widespread throughout the Indo-Pacificregion but are often locally rare and decliningwithin their native range (Walker 1991a,Mueller-Dombois and Fosberg 1998, Kayet al. 2003). On Palmyra Atoll, P. grandis for-est supports indigenous bird’s-nest ferns (As-plenium nidus L.) in the canopy and laua‘efern, Phymatosorus scolopendria (Burm.), in theunderstory. The remainder of the native floraconsists primarily of indigenous strand spe-cies found on many islands in the Pacific,such as beach heliotrope (Tournefortia argen-tea L. f.), Scaevola sericea Vahl, and Pandanustectorius Parkinson. One plant variety is con-sidered endemic to Palmyra: a grass, Lepturusrepens (G. Forst.) R. Br. var. palmyrensis, whichis found in scattered patches throughout theatoll.

The historical record for terrestrial arthro-pod species on Palmyra Atoll is sparse. OttoSwezey published a list of 18 taxa, identifiedat various resolution, collected by Joseph

Rock and Montague Cooke on a 1913 expedi-tion (Swezey 1914). Krauss (1953) reportedan additional 70þ taxa from an expedition in1948, overlapping minimally with Swezey’slist. A comprehensive assessment of the ter-restrial arthropod fauna has never been per-formed, and it is not known whether anynative arthropods persist, aside from four spe-cies of abundant land crabs—B. latro, Cardi-soma carnifex (Herbst.), Coenobita brevimanusDana, and Coenobita perlatus H. Milne Ed-wards.

In 2003, we conducted terrestrial arthro-pod surveys on Palmyra Atoll. The goals ofthe study were to: (1) compile a current listof terrestrial arthropod species from con-temporary sampling; (2) determine probablebiogeographic origins or residency status (in-troduced, indigenous, or endemic) for all taxa;(3) compare these lists with the record fromhistorical expeditions; and (4) assess potentialthreats to native species and ecosystem integ-rity. These surveys were necessary to developa management and conservation plan forthe terrestrial resources and biodiversity ofPalmyra Atoll. We report an important newthreat to P. grandis (a facultative mutualismbetween introduced ants and scale insects),review the literature on this association fromother Pacific islands, and provide recommen-dations for quarantine and conservation.

materials and methods

Arthropod Surveys

The terrestrial arthropod fauna was surveyedduring two visits to Palmyra (28 March–1April and 8–18 June 2003), supplemented bysubsequent opportunistic collections. Becauseof the time constraints of the survey expedi-tions and the remoteness of Palmyra Atoll,we were unable to complete detailed quanti-tative sampling. Therefore, no attempt wasmade to quantify population sizes, commu-nity structure, or species richness, or definehabitat associations and islet distributions ofarthropod taxa. The absence of particulartaxa does not preclude their presence on theatoll. However, we are confident that themost common and widespread terrestrial ar-

Palmyra Arthropod Invasions . Handler et al. 487

thropods present on the atoll in 2003 werecollected and identified.

Malaise traps, light traps, and blacklightedsheets were used to sample active cursorialand flying arthropods (Southwood and Hen-derson 2000, Toda and Kitching 2002). Mal-aise traps were set on Cooper, Eastern, Sand,and South Islets and left in place between2 and 5 days. A total of eight malaise trapsamples was taken in March–April and June2003. Bucket-type light traps (Bioquip, Inc.)were set overnight on Cooper (2 trap-nights),Dudley, Lesley, Lost, Sand, and South Islets,for a total of 7 trap-nights in June 2003.

Vegetation was sampled using sweep netsand beating sheets and by visual inspectionand excavation of leaves, flowers, fruits,branches, and bark. To sample the epigeanfauna, several designs of pitfall traps weretested but all failed because of the rapid andpervasive interference of coconut crabs. Soilcores were not taken systematically becauseof the rocky substrate and lack of soil inmany areas. Therefore, we sifted litter andsoils onto beating sheets and collected visiblearthropods with forceps and aspirators. Antswere sampled by baiting with peanut butterand canned lunch meat, as well as opportunis-tic collecting and litter sifting.

Most arthropods were collected into 95%ethanol. Lepidopteran adults collected withlights were killed with ethyl acetate, fieldmounted when possible, and stored in desic-cation chambers. With the aid of specialists(see Acknowledgments) and by reference tohistorical museum specimens, all taxa wereidentified to the highest possible taxonomicresolution. For taxa identified to genus orspecies, biogeographic origins and residencystatus were inferred from professional com-munication and the literature (e.g., Nishida2002).

In addition to the specimens collected dur-ing these surveys, we have included speci-mens collected during focused ant surveys in2001 and 2004 (M. Richardson, unpubl. data;P. Krushelnycky and P. Lester, unpubl. data),mosquito surveys in 2002 (Depkin 2002), andopportunistic collections between 2003 and2005 (A.T.H. and M.W.L.). Voucher speci-mens are deposited at the Bishop Museum

and at the University of Hawai‘i Insect Mu-seum (Honolulu, Hawai‘i).

results

We recognized 113 arthropod taxa from oursurveys (Figure 2, Appendix). The majorityof taxa were identified to the species level,but some were identifiable only to genus orfamily. Flies (Diptera, 38 species) were themost species-rich, followed by wasps andants (Hymenoptera, 20 species), beetles (Co-leoptera, 19 species), spiders (Araneae, ninespecies), hemipterans (including Heterop-tera and Homoptera, nine species), cricketsand grasshoppers (Orthoptera, six species),and moths (Lepidoptera, six species); theremaining six species belonged to other or-ders. All beetles and ants were unequivocalhistorical introductions, but some flies andother taxa could not be identified to speciesor their biogeographic status could not be de-termined.

Our current surveys added to taxa reportedby historical surveys, bringing the total list to163 taxa recorded from Palmyra since 1913(Appendix). Previously, 88 taxa had been re-corded (Swezey 1914, Krauss 1953), 68 ofwhich were identified to the species level; ofthese, at least 32 were recollected (Figure 3),although voucher specimens for some histor-ically collected taxa could not be located tocompare with contemporary specimens. Oftaxa identified to the species level, 36 speciesrecorded during the two historical surveyswere not recollected, and 51 of 87 (59%)were new records for the atoll.

Of the 119 taxa identified to the specieslevel from Palmyra, most (106 taxa, 89%) arealso recorded from the Hawaiian Islands(Nishida 2002). Most of these (99 species,93%) are considered accidental introductionsto Hawai‘i, whereas only three species (allcoccinellid beetles) were purposefully intro-duced for biological control (Nishida 2002).There is no evidence of intentional introduc-tions to Palmyra; thus all introduced specieson Palmyra are considered accidental intro-ductions. The majority of species now re-corded from Palmyra Atoll fall into this class(102/119, 86%).


Only seven contemporary taxa were classi-fied as indigenous species. These includethree odonates, Anax junius (Drury), Pantalaflavescens (Fabricius), and Ischnura aurora Brau-er; a predaceous tettigoniid katydid, Phisisholdhausi Karny; a marine water strider,Halobates micans Eschscholz; a cranefly, Styr-ingomyia didyma Grimshaw; and an isopod,Australophiloscia societatis (Maccagno) (Appen-dix). All of these species are distributed inthe equatorial Pacific and occur naturallyin similar habitats on neighboring islands(Walker and Deitz 1979, Jin et al. 1991,Nishida 2002, Evenhuis 2005, Harada 2005).The crambid moth Piletocera signiferalis (Wal-lengren) is widespread in the Pacific (Clarke1986) and may be native to Palmyra, but it isunclear to what extent its distribution is natu-ral. Several other taxa are possibly native, butless is known concerning their natural distri-butions or species-level identifications: twospecies of dolichopodid flies (Chrysosoma com-plicatum Becker and Chrysosoma sp. near mo-

lestum Parent) and the gryllid cricket in thegenus Ornebius. Several possibly indigenoustaxa were collected in historical surveys butnot recollected during our trips. These in-clude the tetragnathid spider Tetragnatha key-serlingi Simon, the mirid bug Trigonotylusbrevipes Jakovlev, the gryllid cricket Speonemo-bius tigrinus (Saussure), the butterfly Hypolim-nas bolina Linnaeus (Nymphalidae), and theflies Dasyrhicnoessa insularis (Aldrich), Noctica-nace marshallensis Wirth, Chrysotus javanensisde Meijere, and Olfersia aenescens Thomson.

discussion

Introduced Invertebrates

Although the true extent of native biodiver-sity before human arrival on Palmyra willnever be known, the contemporary terrestrialinvertebrate fauna is dominated by intro-duced species. The great majority of therecorded species are accidentally or purpose-

Figure 2. Summary of introduced, native, and cryptogenic species richness within arthropod orders from recent col-lections, 2003–2005.


fully introduced species also reported fromthe Hawaiian Islands (106/119, 89% [Nishida2002]). Thus, we suggest that Hawai‘i was thepredominant historical source of exotic ar-thropod propagules, most likely during theperiod of heavy military occupation and tran-sit (1938–1961). Military installations havebeen blamed for other introductions of pes-tiferous tramp species to Hawai‘i during thattime period (e.g., Argentine ant, Linepithemahumile [Zimmerman 1941]), and Hawai‘i hasalways been the dominant shipping connec-tion to Palmyra Atoll (Dawson 1959).

Krauss (1953) reported almost no overlapof the 70þ taxa encountered in 1948 withthose recorded during the surveys reportedby Swezey (1914)—the earwig Euborellia an-nulipes (Lucas) was the only species confirmedfrom both surveys. Our recent collectionsshow a somewhat higher ratio of overlap withprevious collections (Figure 3). This may re-

flect the greater comprehensiveness of ourrecent assessments, or it may suggest that theintroduction rate has tailed off since the peakof human activity (i.e., military occupation)ceased in 1961. Still, there was a surprisingdegree of nonoverlap between our collectionsand species lists from Swezey (1914) andKrauss (1953). Of the 87 identified specieswe collected, 52 (63%) were not recorded inhistorical surveys.

No species were clearly endemic to Pal-myra (Appendix), but because any endemicspecies would be undescribed, it remains pos-sible that endemic species exist among thespecimens not identified to the species level.Nevertheless, invasive arthropod species dom-inated the atoll in terms of overall richnessand qualitative abundance. For most of thesespecies, there is little information on theireffects on native species or ecosystem func-tion. However, two groups of invasive insects

Figure 3. Species richness of introduced, native, and cryptogenic arthropods collected only in historical (1913, 1948)and recent (2003–2005) collections, and in both sampling periods (shared species). Uncertain historical natives (n ¼ 8,Appendix) are classified as cryptogenic.


that were particularly abundant, with well-documented impacts on native vegetation(ants and hemipteran phloem-feeding insects)are discussed here.

The Pisonia-Pulvinaria-Pheidole Problem

The terrestrial habitats of Palmyra are valuedfor conservation because the atoll featuressome of the largest remaining stands ofP. grandis forest (Wester 1985, Mueller-Dombois and Fosberg 1998). Pisonia grandisoccurs primarily on small islands throughoutthe tropical Indo-Pacific where seabirds nest(St. John 1951, Airy-Shaw 1952, Stemmerik1964, Mueller-Dombois and Fosberg 1998,Burger 2005). The distribution of P. grandisis usually attributed to both the spread ofseeds stuck to the feathers of seabirds andgrowth facilitated by bird guano (Airy-Shaw1952, Stemmerik 1964, Burger 2005). As thedominant native tree on Palmyra, P. grandisis a characterizing feature of the terrestrialecosystem and provides nesting and roostingsites for seabirds, especially white terns, Gygisalba (Sparrman), and black noddies, Anousminutus Boie. Walker (1991a) found that thesize of breeding colonies of black noddieswas positively associated with the areal extentand maximum height of P. grandis stands onGreat Barrier Reef islands. The height ofthe canopies may provide protection from in-troduced black rats, which can prey on adultbirds and nestlings (Stapp 2002). Moreover,these forests on coralline substrates, in com-bination with the high densities of nestingseabirds, create a phosphate-rich humic soilsubstrate not otherwise found on oceaniccays and atolls (Walker 1991a, Mueller-Dombois and Fosberg 1998). A healthy standtends to contain limited understory growth—and invasion by nonindigenous plants—because the broad-leaved, tall canopy pre-vents most light from reaching the forestfloor.

Pisonia grandis stands throughout theirrange are disappearing quickly because ofanthropogenic habitat destruction andhuman-induced infestations by nonnative in-sects (Mueller-Dombois and Fosberg 1998,

Kay et al. 2003). Repeated defoliation eventsand eventual death of many large trees havebeen observed since 2003 (Figure 4). Concur-rent with these defoliation events, the esti-mated spatial extent of healthy P. grandisstands decreased more than 30% from 2002to 2005, and the stands were increasinglyfragmented (Figure 5) (A. Wegmann, unpubl.data). Currently, numerous invading inver-tebrates may be acting synergistically tothreaten the viability of the P. grandis popula-tion on Palmyra Atoll. Quantitative data areneeded to unambiguously ascribe causes andeffects; here, we document the resident ar-thropod species and review the literature per-tinent to this phenomenon.

At least 10 species of ants were found inrecent surveys, the most notorious of whichare the African big-headed ant, Pheidole mega-cephala (Fabricius); crazy ants Paratrechinabourbonica (Forel) and P. vaga (Forel); andthe Guinea ant, Tetramorium bicarinatum(Nylander). Ants were present in high den-sities throughout the atoll, but Ph. mega-cephala was the dominant species on mostislets. On islets where Ph. megacephala wasnot found, T. bicarinatum and Paratrechinabourbonica were the local dominant species.Introduced ants and other social insects (e.g.,paper wasp Polistes aurifer Saussure) can bedevastating generalist predators of native in-sects on oceanic islands where native socialinsects are depauperate or entirely lacking(Cole et al. 1992, Wilson 1996, Gerlach2004, Krushelnycky et al. 2005, Le Bretonet al. 2005).

In 2003, we observed these ants farming anunrecorded scale insect, Pulvinaria urbicola(Cockerell & Parrott), on P. grandis leaves.Although unidentified at the time, an out-breaking insect was observed on P. grandis inclose association with ants as early as August2001 (Depkin 2002). By March 2002, Depkinreported that mature trees infested with theseinsects on one of Palmyra’s larger islets(Eastern) had lost >50% of their leaves.Nest loss of seabirds using P. grandis forbreeding purposes in the infested zones wasdescribed in the report as an indirect effectof the scale infestation due to weakened


Figure 4. (A) Healthy Pisonia grandis, and (B) Pisonia grandis infested with Pulvinaria urbicola (photos by A.T.H. inJune 2003).

branches (Depkin 2002). Higher rates of P.grandis deadfall were also noted in infestedstands, and areas that had been fully shadedby these trees in 2001 were exposed to directsunlight 1 yr later (Depkin 2002).

Pulvinaria urbicola is a widespread pest ofsolanaceous crops that has been implicated inthe poor health and dieback of P. grandisstands throughout the Indo-Pacific region.In the Seychelles, stress caused by Pu. urbicolascales tended by the long-legged ant, Anoplo-lepis gracilipes (F. Smith), caused defoliationand death of mature trees (Hill et al. 2003).On multiple islands on the Great Barrier

Reef of Australia, green scales tended by Ph.megacephala have locally extirpated mature P.grandis stands, leading to dramatic shiftsfrom closed canopy to open scrub (Olds et al.1996, Smith and Papacek 2001, Kay et al.2003). Pulvinaria urbicola also has been linkedto poor health and dieback of P. grandis treeson Rose Atoll in American Samoa ( J. Burgett,pers. comm.).

Because there have been very few inverte-brate assessments for Palmyra, the local his-tory of this ant-scale association is not wellknown. However, ants have been in Palmyrafor at least a century. Tetramorium bicarina-

Figure 5. Extent of vegetated ground area covered by Pisonia grandis on Palmyra Atoll in 2002 and 2005. In 2002, P.grandis covered approximately 12% of vegetated land area (27.3 ha). The percentage was approximately 8% in 2005(18.2 ha). Data and figure are courtesy of Alex Wegmann.


tum was reported as ‘‘very abundant’’ on theatoll in the early 1900s (Swezey 1914), andPheidole megacephala (recorded as Pheidole sp.but presumed to be Ph. megacephala) invadedbefore 1948 (Krauss 1953). It is probablethat other introduced ant species were pres-ent but uncollected during those surveys.However, because of its ecological domi-nance in numerous habitats globally and asobserved on Palmyra Atoll (e.g., Illingworth1927, Hoffman et al. 1999), it is unlikely thatPh. megacephala was overlooked if presentduring Swezey’s survey. The scale insect Pu.urbicola was not recorded in either of the pre-vious surveys on the atoll, and its negative ef-fects on the P. grandis forest have been notedonly recently. In light of this information, wepropose that Pu. urbicola is a recent introduc-tion to Palmyra Atoll.

Introduced natural enemies can be a viablemeans of control for pestiferous arthropods(Hajek 2004), and several parasitoid speciesused for Pulvinaria spp. control in otherlocations (Smith and Papacek 2001) were col-lected in our surveys. We collected the aphe-linid wasps Coccophagus ceroplastae (Howard)and Euryischomyia flavithorax Girault &Dodd and the encytrid wasp Metaphycus flavus(Howard), which are all known to includePulvinaria spp. in their host ranges. Severalcoccinellid beetle species also occur on Pal-myra, including Coelophora inaqualis (Fabri-cius), Diomus notescens (Blackburn), andRhyzobius lophanthae (Blaisdell). However,these insects were relatively uncommon,wasp parasitism rates were quite low (meanexit holes per insect on Eastern Islet ¼2.1%G 0:7 S.E. [Krushelnycky and Lester,unpubl. data]), and Pu. urbicola does notappear to be under control. Smith andPapacek (2001) advocated the release of Cryp-tolaemus montrouzieri Mulsant to augment thepresence of the parasitic wasp C. ceroplastae inthe Coringa-Herald National Nature Reservein the Coral Sea. They argued that parasitoidwasps can regulate scales at low densities, butoutbreaks must be controlled with augmenta-tive releases of generalist predators.

Ants in general, and Ph. megacephala spe-cifically, often interfere with other natural en-

emies of Hemiptera used in biological control(Reimer et al. 1993, Jahn and Beardsley 1994,2000, Helms and Vinson 2002, Lach 2003).Ants form facultative mutualisms with mealy-bugs, scales, aphids, planthoppers, and otherhemipterans by protecting them from preda-tors and parasitoids and moving them amongindividual host plants while harvesting honey-dew, the sugary exudate upon which the antsfeed (Buckley 1987). Thus, both ant and scaledensities can reach higher population levelsthan either species could attain in isolation,with devastating effects on host plants andvegetation structure (O’Dowd et al. 2003).Pheidole megacephala also attended thick ag-gregations of Dysmicoccus neobrevipes Beards-ley (Pseudococcidae) around the fruits ofthe rare indigenous tree Ochrosia oppositifolia(Lam.) K. Schum. The cottony-cushion scale(Icerya purchasi Maskell) and an unidentifiedsooty mold (Capnodiaceae) were observed onSceavola sericea, and sooty mold commonlygrew on laua‘e fern (Phymatosorus scolopendri)under P. grandis canopies infested with Pu.urbicola. The opaque coating of sooty moldson plant surfaces, encouraged by the richsugar content of hemipteran honeydew‘‘rain’’ (Wood et al. 1988), can reduce lightinterception and photosynthesis, thus increas-ing stress on recipient plants (Fokkema et al.1983).

conclusions

Despite the fact that the flora and fauna ofPalmyra have already been overwhelmed bynonnative species, globally important standsof P. grandis and dependent seabird popula-tions remain. Yet the atoll remains highlysusceptible to new introductions of invasivespecies. This is clearly demonstrated by therecent decline of P. grandis, which we pro-pose is caused by recent introductions of scaleinsects and accelerated by ants. Hawai‘i accu-mulates 20–30 new foreign insect species peryear (Beardsley 1962), and the small island ofGuam receives 12–15 new species (Schreinerand Nafus 1986), many of which become im-portant pests to agriculture and native spe-cies. Even with the extremely limited human


transit to Palmyra, more recent introductionscontinue.

Indeed, a new unidentified whitefly in thefamily Aleyrodidae (Hemiptera) was discov-ered on the atoll in 2005, and it quicklyreached nuisance levels on Scaevola speciesand other native plants on Cooper Islet. Theresearch field station, housing, and airplanerunway are located on Cooper; therefore amajority of the current human traffic and im-pact on Palmyra Atoll is concentrated on thatparticular islet. The family Aleyrodidae hasnot previously been recorded from Palmyra,either by ourselves or in previous surveys(note that the insect referred to as a ‘‘white-fly’’ by Depkin [2002] proved to be the scaleinsect Pu. urbicola, not a true whitefly). In lessthan 2 yr, this presumably recent introduc-tion has gone from being absent or undetect-able to a major nuisance, with predictednegative impacts on the native flora (Byrneand Bellows 1991).

In response to Ph. megacephala and Pu.urbicola infestations in the P. grandis forestsof the Capricorn Cays National Park ofQueensland, Australia, Kay et al. (2003) rec-ommended strategies to fight these infesta-tions, including (1) annual censuses ofhabitats to monitor infestation levels, (2) im-plementation of a biocontrol program usingthe ladybird beetle Cryptolaemus montrouzieriand parasitoid wasps in combination with antcontrol measures, and (3) development andimplementation of an integrated revegetationand weed control program. In light of thisant-scale infestation on Palmyra and the de-clining P. grandis, we recommend the con-tinued implementation of control measuresfor both ants and scales, which are currentlyongoing. More experimental data are urgentlyneeded to determine the individual and com-bined effects of ants and scales on P. grandisat this location. Generally, introduction ofnew biological control measures (e.g., Crypto-laemus montrouzieri) should proceed with theutmost caution, to avoid nontarget impactsand other documented pitfalls (e.g., Pearsonand Callaway 2003, Simberloff 2005). In thecurrent case, nontarget impacts of specializednatural enemies are less likely because all in-

sects collected from the hemipteran suborderSternorrhyncha were unequivocal introducedspecies. Of course, all mitigation and controlmeasures should be accompanied with moni-toring measures to assess the efficacy of treat-ments and to test the causal mechanismsproposed in this paper. In the near term, a vi-able option would be to propagate P. grandissaplings in greenhouses protected from antsand scales. Even after the destructive impactsof mining and goat grazing, P. grandis is capa-ble of repopulating an area after substantialdisturbances (Elsol 1985, Walker 1991b) ifpestiferous impacts can be minimized. How-ever, this task will be more difficult if a com-plete phase shift to coconut palms or openscrubland has already occurred (Kay et al.2003).

Moreover, effective management protocolsfor Palmyra Atoll should include an enforce-able quarantine policy. Primary pathways oftransmission of invasive species include hitch-hiking on cargo in transit such as fresh pro-duce, plants, and packing material (Reichardand White 2001). These items should be in-spected in detail, and high-risk categories(i.e., live plants) should be completely prohib-ited from transport to Palmyra. In addition,docking recreational craft should be scruti-nized for the possibility of infestation by antsor plant pathogens and pests. Because trafficto and from the atoll is relatively limited, im-plementation of a robust quarantine policy, inwhich all cargo is thoroughly inspected ortreated, should be feasible.

acknowledgments

We thank the Bishop Museum for access tocollections and working space. Thanks alsoto Keith Arakaki, Joe Beatty, Ron Englund,Neal Evenhuis, Michael Gates, Tino Gon-salves, Bertram Lindsey, Gary Miller, JohnNoyes, Dan Polhemus, Neil Reimer, and G.Allan Samuelson for identification and verifi-cation of insect specimens. Nathan Sanders,Robert Cowie, Phil Lester, and two anony-mous reviewers provided critical commentson the manuscript, and Stephanie Dunbar,Paul Krushelnycky, Alex Wegmann, Zenneth


Compania, Frank Lau, Emilia Wiggins, Jes-sica Rodrigues, Mari Oishi, Alex Duffy, andElizabeth Lange assisted on the ground. Spe-cial thanks are due Alex Wegmann for pro-viding the data and map for Figure 5.

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Appendix

Taxonomic List of Terrestrial Arthropod Species Collected from Palmyra Atoll in Historical (Swezey 1914,Krauss 1953) and Recent (2001–2005) Collections

Collectionsc

Family Taxaa Originb 1913 19482001–2005 Determinerd

Order AraneaeAgelenidae Agelenidae G. sp. ? —

p—

Araneidae Neoscona theisi (Walckenaer, 1841) Intr —p p

DG & JBHeteropodidae Heteropoda venatoria (Linnaeus, 1767) Intr —

p pJB

Pholcidae Smeringopus pallidus (Blackwall, 1856) Intr —p p

DG & JBSalticidae Hasarius adansoni (Audouin, 1826) Intr —

p pJB

Menemerus bivittatus (Dufour, 1831) Intr —p p

JBMessua cf. felix (Peckham & Peckham, 1901) Intr —

p pJB

Phintella versicolor (C. L. Koch, 1846) ? — —p

* JBPlexippus paykulli (Audouin, 1826) Intr —

p—

Salticidae G. sp. 1 ? — ?p

Salticidae G. sp. 2 ? — ?p

Sandalodes sp. ? —p

—Scytodidae Scytodes longipes Lucas, 1845 Intr —

p—

Scytodes striatipes (L. Koch, 1872) Intr —p

—Tetragnathidae Tetragnatha keyserlingi Simon, 1890 Nat? —

p—

Theridiidae Coleosoma floridanum Banks, 1900 Intr —p

—Latrodectus geometricus C. L. Koch, 1841 Intr —

p—

Nesticodes rufipes (Lucas, 1846) Intr —p

—Order Blattodea

Blaberidae Pycnoscelus indicus (Fabricius, 1775) Intr — —p

* DGBlatellidae Supella longipalpa (Fabricius, 1798) Intr — —

p* DG

Blattidae Periplaneta americana (Linnaeus, 1758) Intr —p

—Periplaneta australasiae (Fabricius, 1775) Intr —

p pDG

Platyzosteria soror (Brunner, 1865) Intr —p

—Order Coleoptera

Anthribidae Araecerus vieillardi (Montrouzier, 1860) Intr — —p

* GASMauia subnotatus (Boheman, 1859) Intr — —

p* GAS

Carabidae Carabidae G. sp. ? —p p

GASCerambycidae Cerambycidae G. sp. 1 ? — —

p* GAS

Cerambycidae G. sp. 2 ? — —p

* GASCoccinellidae Coccinellidae G. sp. ? — —

p* GAS

Coelophora inaequalis (Fabricius, 1775) Intr — —p

* GASDiomus notescens (Blackburn, 1889) Intr ?

p—

Rhyzobius lophanthae (Blaisdell, 1892) Intr ?p

—Cryptophagidae Toramus(?) sp. ? —

p—

Cucujidae Psammoecus insularis (Sharp, 1885) Intr — —p

* GASElateridae Conoderus pallipes (Eschscholtz, 1829) Intr ?

p pGAS

Melanoxanthus melanocephalus (Fabricius, 1781) Intrp

— —Hydrophilidae Dactylosternum abdominale (Fabricius, 1792) Intr — —

p* GAS

Nitidulidae Carpophilus humeralis (Fabricius, 1798) Intr — —p

* GASOedemeridae Eobia bicolor (Fairmaine, 1849) Intr —

p pGAS

Eobia decolor (Fairmaine, 1849) Intr —p p

GASEobia kanack (Fairmaine, 1849) Intr

p—

pGAS

Eobia sinensis Gemminger, 1870 Intr — —p

* GASSessinia livida (Fabricius, 1775) Intr — —

p* GAS

Pselaphidae Pselaphidae G. sp. ? —p

—Ptilidae Ptilidae G. sp. ? —

p pGAS

Scarabaeidae Saprosites pygmaeus Harold, 1877 Intr —p

—Scolytidae Xyleborus perforans (Wollaston, 1857) Intr — —

p* GAS

Staphylinidae Philonthus discoideus (Gravenhorst, 1802) Intr — —p

* GAS


Appendix (continued)

Collectionsc


Order DermapteraCarcinophoridae Euborellia annulipes (Lucas, 1847) Intr

p p pWH

Order DipteraAgromyzidae Liriomyza sativae Blanchard, 1938 Intr — —

p* KA

Liriomyza sp. ? — —p

* KACalliphoridae Chrysomya megacephala (Fabricius, 1794) Intr —

p—

Lucilia sericata (Meigen, 1826) Intr —p p

KACanaceidae Canaceoides sp. ? — —

p* KA

Nocticanace marshallensis Wirth Nat? —p

—Ceratopogonidae Ceratopogonidae G. sp. ? — —

p* KA

Dasyhelea sp. ? —p p

KAChironomidae Chironomidae G. sp. ? —

p—

Clunio sp. ? — ?p

KAChloropidae Cadrema pallida (Loew, 1865) Intr —

p pKA

Gaurax bicoloripes (Malloch, 1933) Intr — —p

* KAHippelates sp. ?

p— —

Culicidae Aedes albopictus (Skuse, 1894) Intr — —p

*e GASCulex quinquefasciatus Say, 1823 Intr — —

p*e GAS

Dolichopodidae Chrysosoma complicatum Becker, 1922 Intr — —p

* KAChrysosoma globiferum (Wiedemann, 1830) Intr

p— —

Chrysosoma sp. ? —p p

KAChrysosoma sp. nr. molestum Parent ? — —

p* KA

Chrysotus javanensis de Meijere, 1916 Nat? —p

—Dolichopodidae G. sp. ? ? ?

pKA

Drosophilidae Cacoxenus perspicax (Knab, 1914) Intr — —p

* KADrosophila ananassae Doleschall, 1858 Intr — —

p* KK

Ephydridae Discocerina mera Cresson, 1939 Intr —p p

KAHecamede granifera (Thomson, 1869) Intr —

p—

Hostis guamensis Cresson, 1945 Intr —p

—Placopsidella marquesana (Malloch, 1933) Intr —

p—

Placopsidella sp. ? — ?p

KAScatella stagnalis (Fallen, 1813) Intr — —

p* KA

Hippoboscidae Olfersia aenescens Thomson, 1869 Nat? —p

—Limoniidae Limonia sp. nr. perkinsi (Grimshaw) Intr — —

p* KA

Styringomyia didyma Grimshaw, 1901 Nat —p p

KALonchaeidae Lamprolonchaea metatarsata (Kertesz, 1901) Intr —

p pKA

Milichilidae Milichiella lacteipennis (Loew, 1865) Intr — —p

* KAMuscidae Atherigona orientalis Schiner, 1868 Intr —

p pKA

Atherigona sp. ? — —p

* KA & NEMusca domestica Linnaeus, 1758 Intr —

p—

Muscidae G. sp. ? — —p

* KAPhoridae Chonocephalus sp. ? — —

p* KA

Platystomatidae Scholastes lonchifera Hendel, 1914 Intr —p p

KASarcophagidae Parasarcophaga misera Walker Intr — —

p* KA

Parasarcophaga sp. ? — —p

* KASarcophaga peregrina (Robineau-Desvoidy, 1830) Intr —

p—

Sarcophagidae G. sp. ? — —p

* KASciaridae Sciaridae G. sp. ? — —

p* KA

Stratiomyidae Cephalochrysa maxima (Bezzi, 1928) Intr — —p

* KASyrphidae Eristalinus arvorum (Fabricius, 1787) Intr — —

p* WH

Simosyrphus grandicornis (Macquart, 1842) Intr —p

—Syritta sp. ? — —

p* KA

Tethinidae Dasyrhicnoessa insularis (Aldrich, 1931) Nat? —p

—Tethina sp. ? — —

p* KA

Ulididae Ulididae G. sp. ? — —p

* KA



Collectionsc


Order Hemiptera (Heteroptera)Cynidae Geotomus pygmaeus (Dallas, 1851) Intr — —

p* WH

Gerridae Halobates micans Eschscholz, 1822 Natp

—p

DPLygaeidae Lygaeidae G. sp. ? — —

p*

Miridae Trigonotylus brevipes Jakovlev, 1880 Nat? —p

—Reduviidae Reduviidae G. sp. ? — —

p*

Order Hemiptera (Sternorrhyncha)Aleyrodidae Aleyrodidae G. sp. Intr — —

p*

Aphididae Aphididae G. sp. ?p

—p

Coccidae Pulvinaria urbicola (Cockerell & Parrott, 1899) Intr — —p

* BLMargarodidae Icerya purchasi Maskell, 1879 Intr —

p pWH

Pseudococcidae Dysmicoccus brevipes (Cockerell, 1893) Intr —p

—Dysmicoccus neobrevipes Beardsley, 1959 Intr — —

p* GM

Ferrisia virgata (Cockerell, 1893) Intr —p

—Planococcus citri (Risso, 1813) Intr —

p—

Order HymenopteraAphelinidae Coccophagus ceroplastae (Howard, 1895) Intr — —

p* DG & MG

Euryischomyia flavithorax Girault & Dodd, 1915 Intr — —p

* DGCynipidae Kleidotoma sp. ? —

p—

Diapriidae Trichopria sp. ? —p

—Encyrtidae Metaphycus flavus (Howard, 1881) Intr — —

p* DG & JN

Eulophidae Aprostocetus hagenowii (Ratzeburg, 1852) Intr —p

—Hemiptarsenus semialbiclavus (Girault, 1916) Intr — —

p* MG

Evaniidae Evania appendigaster (Linnaeus, 1758) Intr — —p

* WHFormicidae Cardiocondyla emeryi Forel, 1881 Intr — —

p* PK

Cardiocondyla minutior Forel, 1899 Intr — —p

* PKHypoponera punctatissima (Roger), 1859 Intr — —

p*f PK

Monomorium floricola ( Jerdon, 1851) Intr — —p

* DGParatrechina bourbonica (Forel, 1886) Intr — —

p* NR

Paratrechina longicornis (Latreille, 1802) Intr — —p

*g

Paratrechina vaga (Forel, 1901) Intr — —p

* NRPheidole megacephala (Fabricius, 1793) Intr —

p pNR

Tapinoma melanocephalum (Fabricius, 1793) Intr — —p

* WHTetramorium bicarinatum (Nylander, 1847) Intr

p—

pDG

Megachilidae Megachile fullawayi Cockerell, 1914 Intr —p

—Megachile sp. ? — —

p* WH & TG

Scelionidae Scelionidae G. sp. ? — —p

* MGSphecidae Sceliphron caementarium (Drury, 1770) Intr — —

p* TG

Sphecidae G. sp. ? — —p

* WHVespidae Pachodynerus nasidens (Latreille, 1802) Intr —

p pWH

Polistes aurifer Saussure, 1853 Intr —p p

TGOrder Isopoda

Philosciidae Australophiloscia societatis (Maccagno, 1932) Nat — —p

* DGOrder Lepidoptera

Agonoxenidae Agonoxena argaula Meyrick, 1921 Intr —p

—Cosmopterigidae Anatrachyntis incertulella (Walker, 1864) Intr

p— —

Crambidae Piletocera signiferalis (Wallengren, 1860) ? —p p

WHGelechiidae Stoeberhinus testaceus Butler, 1881 Intr —

p pWH

Gracillariidae Gracillariidae G. sp. ? — —p

* WHNoctuidae Chrysodeixis eriosoma (Doubleday, 1843) Intr —

p—

Spodoptera litura (Fabricius, 1775) Intr — —p

* WHNymphalidae Hypolimnas bolina Linnaeus, 1758 Nat? —

p—

Sphingidae Agrius cingulata (Fabricius, 1775) Intr — —p

* WHTineidae Erechthias simulans (Butler, 1882) Intr — —

p* WH

Opogona sp. ? —p

—



Collectionsc


Order OdonataAeshnidae Anax junius (Drury, 1770) Nat — —

p* DG

Coenagrionidae Ischnura aurora Brauer, 1865 Nat — —p

* RELibellulidae Crocothemis servilia (Drury, 1770) Intr — —

p* RE

Pantala flavescens (Fabricius, 1770) Nat —p p

DGOrder Orthoptera

Acrididae Oxya japonica (Thunberg, 1824) Intr —p p

DGGryllidae Cycloptilum sp. ? —

p—

Ornebius sp. ? — —p

* WHSpeonemobius tigrinus (Saussure) Nat? —

p—

Teleogryllus oceanicus (Le Guillou, 1841) Intr — —p

* WHPyrgomorphidae Atractomorpha sinensis Bolivar, 1905 Intr —

p pWH

Tettigoniidae Conocephalus saltator (Saussure, 1859) Intr —p p

WHPhisis holdhausi Karny, 1926 Nat

p p pWH

a G. sp. indicates undetermined genus and species.b Refers to biogeographic status on Palmyra (Intr, introduced; Nat, native; ?, cryptogenic).c A check mark (

p) indicates that a taxon was collected during a particular time period, as opposed to no collection (-) or an un-

confirmed record (?). An asterisk (*) for recent collections indicates a new record for Palmyra Atoll.d Abbreviations refer to: BL, Bertram Lindsey; DG, Daniel Gruner; DP, Dan Polhemus; GAS, G. Allan Samuelson; GM, Gary

Miller; JB, Joe Beatty; JN, John Noyes; KA, Keith Arakaki; KK, Ken Kaneshiro; MG, Michael Gates; NR, Neil Reimer; RE, RonEnglund; TG, Tino Gonsalves; WH, William Haines.

e Collected July 2002 by C. Depkin.f Collected November 2003 by P. Krushelnycky and P. Lester.g Collected November 2003 by M. Richardson.


arthropod surveys on palmyra atoll, line islands, and ... · 485 arthropod surveys on palmyra...

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