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POPULATION ECOLOGY

Influence of Plant Community Structure on Natural Enemies ofPine Needle Scale (Homoptera: Diaspididae) in

Urban Landscapes

JOHN F. TOOKER AND LAWRENCE M. HANKS

Department of Entomology, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Environ. Entomol. 29(6): 13051311 (2000)

ABSTRACT Pine needle scale, Chionaspis pinifoliae (Fitch), is a pest of many species of conifersin urban habitats and Christmas tree farms. We found that the scale was abundant in impoverishedhabitats, such as ornamental landscapes, and scarce in more natural, park-like habitats. Rates ofparasitism were highest in impoverished habitats, suggesting that parasitoids were not effective insuppressing scale populations. Generalist predators, however, were more diverse and abundant in

natural habitats and appear to be more effective in controlling scales in structurally complex plantcommunities. Total densities of arthropods and densities of plant-feeding species were greatest inimpoverished habitats, suggesting that populations were poorly regulated. Outbreaks of pine needlescale in ornamental landscapes and Christmas tree farms may be discouraged by increasing plantstructural and species diversity to favor natural enemies.

KEY WORDS Aphelinidae, Aphytis, Chionaspis heterophyllae, habitat effects, natural enemies,conservation biological control

IN BOTH NATURAL and managed ecosystems, speciesdiversity of arthropod natural enemies is often posi-

tively correlated with the diversity of plant species(e.g., Risch 1981, Yue et al. 1994, Dean and Milton1995). Plants sustain populations of naturalenemies byproviding prey, oral resources for adults,and suitablemicroclimates (Powell 1986, van Emden 1990). Thus,diversifying the composition of plant communitiescould encourage natural enemies to suppress popula-tions of phytophagous insects. Ornamental landscapesare amenable to this pest management tactic becausethey are relatively stable ecosystems and are not con-strained by the simple structure and periodic disrup-tion characteristic of agronomic systems (Raupp et al.1992). Diverse and structurally complex plant com-

munities in ornamental landscapes support a higherdiversity and abundance of natural enemies, resultingin better regulation of phytophagous insects (e.g.,Hanks and Denno 1993, Shrewsbury 1996).

We examined the inuence of plant communitystructure of urban landscapes on the abundance anddiversity of natural enemies, and, indirectly, on pop-ulation densities of pine needle scale, Chionaspis pini-

foliae (Fitch). Pine needle scale is native to NorthAmerica (Burden and Hart 1989), but is a serious pestof many species of introduced evergreens, includingspecies in the Pinaceae (Abies, Picea, Pinus, Pseudot-

suga, and Tsuga), Cupressaceae (Juniperus), and Tax-aceae (Taxus, Torreya; Shour and Schuder 1987). Thescale is one of the most important pests of ornamentalpines in the United States, and has been labeled thewhite malady because heavily infested trees appearwhitewashed (Johnson and Lyon 1988).

Damaging infestations of pine needle scale are usu-ally limited to managed ecosystems, such as nurseries,

tree farms, and ornamental landscapes (Johnson andLyon 1988) that are often characterized by low levelsof plant species diversity and structural complexity(Raupp et al. 1992). The scale is rare in more naturalhabitats, such as forests and wood lots (Ruggles 1931)where complexity and plant diversity are higher (seeRisch 1981, Szentkiralyi and Kozar 1991, Yue et al.1994, Dean and Milton 1995). Natural enemies of pineneedle scale include coccinellid beetles (Cumming1953, Nielsen and Johnson 1973, Luck and Dahlsten1974, Eliason and McCullough 1997) and at least ninespecies of aphelinid parasitoids (Krombein et al. 1979;

Burden and Hart 1989, 1993), but the scale is alsoprobably attacked by more generalist predators ofarmored scale insects, including harvestmen, crickets,earwigs, and neuropteran larvae (Clausen 1940, 1978;Crumb et al. 1941; Cloudsley-Thompson 1958; Ebling1978; Hanks and Denno 1993).

In this study, we examined the inuence of plantcommunity structure withinurban landscapes on ratesof predation and parasitism of pine needle scale, scalepopulation density, and the abundance and speciesdiversity of the arthropod community as a whole. Inanother portion of this study, we excluded preda-

tors from the study trees to better evaluate the im-pact of parasitoids on scale populations. Finally, wetested the ability of natural enemies to disperse shortdistances, which is of interest because of the smallspatial scale of ornamental landscapes where the scaleis a pest.

0046-225X/00/13051311$02.00/0 2000 Entomological Society of America


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Materials and Methods

Chionaspis pinifoliae has long been confused withChionaspis heterophyllae Cooley, the pine scale, be-cause of similar appearance and natural history(Shour1986, Kosztarab 1996). Both species overwinter in theegg stage (Kosztarab 1996) and crawlers of both spe-

cies emerge synchronously in spring and summer. Thetwo species also share parasitoid species (Burden andHart1993). Differences in phenology and morphologyare too subtle to distinguish C. pinifoliae from C. het-erophyllae in the eld (Shour 1986). The two speciesalso overlap in geographic distribution, C. pinifoliaeoccurring over most of North America while C. het-erophyllae is conned to the eastern and midwesternstates (Shour and Schuder 1987, Kosztarab 1996). Forthe purposes of this report, we acknowledge the pres-ence of the two scale species in the area of our study,but refer to the species complex as pine needle scale

(see Johnson and Lyon 1988).Influence of Plant Community Structure on Pop-ulation Density of Pine Needle Scale. We estimatedpopulation densities on pine trees in three types ofurban habitats: (1) impoverished habitats, ornamen-tal landscape plantings with pines in proximity topaved roads or parking lots, and surrounded by gravelor mulch (n 25 sites);(2) turf habitats, ornamentallandscapes with pines surrounded by turf (n 24sites); and (3) wooded habitats, park-like andwooded primarily with pine species (n 24 sites).Study sites were inChampaign-Urbana, IL,and at eachsite there were at least three of the common hosts ofpine needle scale (Shour and Schuder 1987): Pinusmugo Turra (0.252 m tall), Pinus sylvestris L. (1.54m), or Pinus nigra Arnold (2.55 m).

There are apparently no standard protocols for es-timating population densities of scale insects on co-nifers (see Kozar 1990, Jactel et al. 1996). Our initialattempts to estimate density of pine needle scale byrandom sampling proved inaccurate at low densitiesbecause of the patchy distribution of scales withintrees. Instead, we estimated population densities byexamining needles distributed throughout the canopyand counting female scales for a standard 3-min pe-

riod. We counted only scales of the current genera-tion, as evidenced by an intact and pure white cover.This method was reproducible in quantifying densityeven of very lightly infested trees. Similar visual tech-niques have been used to estimate population densi-ties of a variety of arthropod species (e.g., Wilson andSimberloff 1969, McCullough and Sadof 1998, Seboltand Landis 1999). We estimated population densitiesof pine needle scale in June 1997 during the rstgeneration.

Infesting Potted Pines with Scale. We infested smallpine trees with pine needle scale to evaluate the im-

pact of natural enemies on scale populations. Ourpotted pines were 2540 cm tall Scotch pines (P.sylvestris variety French Blue) in plastic pots (1519cm diameter) witha sterilizedpottingmixtureof equalproportionsof soil, peat, andperlite. Pines were pottedin mid-April 1997 and held in a greenhouse under

long-day photoperiod, were watered as needed, andfertilized at 2-wk intervals (15:30:15; Scotts Miracle-Gro Products, Port Washington, NY). We infestedtrees with pine needle scale 1 mo after potting bylaying scale-infested cuttings on them during crawleremergence; cuttings were taken from infested Scotchpine tree (Hoot Owl Christmas Tree Farm, Urbana,IL).After crawlers had settled, we disposed of cuttingsto prevent parasitoids from emerging in the green-house.

Influence of Plant Community Structure on Ratesof Predation and Parasitism. To identify the parasitoidspecies that attacked pine needle scale in our studyarea, we collected scale-infested cuttings and rearedparasitoids in lidded cardboard buckets (17 cm diam-eter, 18 cm high) to whichwas attached a glass vial trap(15 mm o.d.). Parasitoids were stored in 70% ethanoland 10 specimens of each of three morphospecieswere submitted for identication to the USDA Sys-

tematic Entomology Laboratory in Beltsville, MD. Afourth species, discovered later, was identied by J. M.Heraty at the University of California, Riverside.

We caged predaceous arthropods with scale-in-fested needles of Scotch pine to conrm that theywould eat pine needle scale: only species that weremost likely to be predators were tested, includingharvestmen (Opiliones), snowy tree crickets (Oecan-thus fultoni Walker), eld crickets (Gryllus sp.), larvalgreen lacewings (Chrysopidae), and twicestabbedlady beetles [Chilocorus stigma (Say); see Clausen1940, 1978; Crumb et al. 1941; Cloudsley-Thompson

1958; Ebling 1978; Hanks and Denno 1993]. Predatorswere caged individually (n 3 per species) in plasticcontainers with moistened cotton rolls (to providewater) and pine needles having similar densities offemale scales (10 scales) in the second or thirdinstar. After 24 h, we inspected scales for evidence ofpredation, such as damage to scale cover or removal ofthe scale body.

To determine whether rates of predation and par-asitism were inuenced by habitat, we positioned pot-ted Scotch pines infested with scale next to or at thebase of study trees in impoverished turf and woodedhabitats (n 10, 10, 15, respectively) on 1625 June

1997. Scales on both potted and resident trees wereeither second or third instars,the life stages vulnerableto parasitization (unpublished data). Potted pineswere subsequently watered as needed.

After 5 wk, we returned the potted trees to thelaboratory where they were held for 2 wk to allowparasitoids to develop. To estimate the density ofscales per unit of needle length, we arbitrarily selected20 needles from each seedling, counted the number ofadult female scales on each needle, and measuredneedle length. To estimate percent parasitism andpredation, we arbitrarily selected 50 adult female

scales per tree and examined them under a dissectingmicroscope. In many cases the scale insects them-selves were missing, but the condition of their waxcovers provided evidence of activity by any naturalenemies (characterized in part during studies of pre-dation, described above). A circular exit hole was

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evidence of parasitism; predators with chewingmouthparts tore ragged holes in the cover, whereasthose with sucking mouthparts left only the shriveledbodies of their prey. We excluded adult females thathad been killed by fungi, as well as those from theprevious generation, which were identied by havingeither discolored tests or discarded chorions undertheir tests.

Impact of Parasitoids on Scale Populations Exclu-sive of Predators. Predators of pine needle scale ap-parently consumed parasitized scales and even para-sitoid pupae, and therefore could inuence the role ofparasitism in regulation of scale population density. Toexamine the impact of parasitoids in scale populationdensity, we excluded predators from potted pines inwooded habitats where potential natural enemies ofthe scale were most abundant (see below), and mea-sured parasitism rate. To exclude predators, we placeda cylinder of aluminum window screen (1 mm mesh,

60 cm tall) around scale-infested potted trees, closedat the top with staples and secured to the pot with ducttape. Preliminaryexperiments demonstrated thatwin-dow screen excluded most, if not all, predators whilepermitting parasitoids access to scales. Female scaleson potted trees were in the second or third instar. Wepositioned these potted pines next to nine Scotchpines in each of three wooded areas.After 5 wk,pottedpines were returned to the laboratory to estimatepercent parasitism (as described above).

Evaluation of Small-ScaleMovement of Natural En-emies. To evaluate dispersal abilities of natural ene-

mies over small spatial distances, we positioned threescale-infested potted pines (female scales in second orthird instar) in each of three impoverished sites so asto contact the canopy of resident trees. In the samesites, we also positioned three scale-infested pines30 cm from the canopy edge (bare ground or gravelseparated potted pines from resident trees).The studywas set up on 13 August 1997 and potted pines weresubsequently watered as needed. After 5 wk, pineswere returned to the laboratory and held for 2 wk toallow parasitoids to develop, and then scales wereexamined to estimaterates of predation and parasitism(as described above).

Influence of Plant Community Structure on Abun-dance and Diversity of Arthropods. To examine theinuence of habitat on arthropod communities asso-ciated with host plants of pine needle scale, we tookbeating samples of all 73 study trees on 19 June and 27August 1997. Samples were taken at mid-canopy fromfour branches per tree, one at each cardinal point.Each branch wasbeaten four times with a 925-g rubbermallet and falling arthropods were captured in anenamel pan partly lled with 70% ethanol. Branchsamples from each tree were combined into a singlesample.

We categorized all collected arthropods into mor-phospecies and counted the specimens of each. Wefurther categorized these morphospecies into guilds:phytophagous insects, predators, parasitoids, and po-tential predators of pine needle scale (our method ofsampling was not effective in capturing aphelinid

parasitoids). We estimated species diversity of arthro-pods with the Shannon-Wiener index (H; Peet 1974,Hayek and Buzas 1997).

Statistics. We used analysis of variance (ANOVA;SAS Institute 1988) to test the effect of habitat ondensity of pine needle scale per tree, percent parasit-ism, percent predation, arthropod density, and theeffect of proximity to resident pines on percent par-asitism and predation. We determined whether thedata met the assumptions of ANOVA by conrminghomogeneity of variances between treatments (F

max-

test) and normality within treatments (ShapiroWilkstest; Sokal and Rohlf 1995). Data not suitable forANOVA were analyzed by the nonparametricKruskal-Wallis test (Sokal and Rohlf 1995). Differ-ences between individual means were tested by theleast signicant difference (LSD) test (Ott 1993). Wecompared ShannonWiener indices with the Studentt-test (Magurran 1988). Data are presented as means

1 SE unless stated otherwise.

Results

Influence of Plant Community Structure on Pop-ulation Density of Pine Needle Scale. Density of pineneedle scale varied signicantly across habitats andwas highest in impoverished habitats (mean of 60scales/tree/3-min search), intermediate in turf habi-tats (17 scales), and lowest in wooded habitats (twoscales; ANOVA F 11.7; df 2, 62; P 0.0001). Eachmean was signicantly different from the others (LSD

test P

0.05).Influence of Plant Community Structure on Ratesof Predation and Parasitism. Of four parasitoid mor-phospecies reared from scale-infested clippings, threewere aphelinids: Aphytis sp. poss. chilensis Howard,Encarsia aurantii Howard, and Coccobius varicornis(Howard). The fourth parasitoid species was in thegenus Zagrammosoma (Hymenoptera: Eulophidae),most species of which are believed to be parasitoids ofleafminers (Schauff et al. 1997). The relatively largebody size of the Zagrammosoma sp. (23 mm long)also suggests it is probably not a parasitoid of pineneedle scale and that it emerged from other hosts on

our pine clippings.Snowy tree crickets, eld crickets, and green lace-

wing larvaeallreadily fed on female pine needle scalesin cages. Twicestabbed ladybird beetles and harvest-men did not eat scales on individual needles, but didso on scale-infested Scotch pine trees in an indepen-dent laboratory experiment. Thus, we considered allof these species potential predators of pine needlescale.

On scale-infested potted pines placed in the eld,parasitism rate was highest in impoverished habitats(where the scale was most abundant), intermediate in

turf habitats, and very low in wooded habitats (wherethe scale was rare; means signicantly different;KruskalWallis statistic 16.7, df 2, P 0.0002;Table 1).Parasitism rates across all threehabitats weresignicantly and positively correlated with host abun-dance on resident trees (Fig. 1), at least at the spatial

December 2000 TOOKER AND HANKS: NATURAL ENEMIES RELATIONS OF PINE NEEDLE SCALE 1307


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scale of individual potted trees. This suggests thatparasitoids were more abundant in areas where den-sities of pine needle scale were high. Parasitism ratewas not correlated with scale density of individualpotted pines (regression analysis, t 0.42; P 0.67).Predation rates of pine needle appeared to be highestin impoverished habitats, but differences between

habitats were not statistically signicant (ANOVA,F 0.107; df 2, 61; P 0.89; Table 1).Impact of Parasitoids on Scale Populations Exclu-

siveof Predators. Evenwhenpredators were excludedby caging pine trees with aluminum screen, parasitismrates of scales in wooded habitats were very low(0.0034 0.003; n 9), suggesting that parasitoidswere scarce in that habitat.

Evaluation of Small-Scale Movement of Natural En-emies. Neither parasitism nor predation rates of pineneedle scale differed signicantly between pottedpines positioned in contact with foliage of residenttrees (parasitism rate0.71 0.08, predation rate0.11 0.03) andthose positioned 30 cm away (parasitism rate0.62 0.10, predation rate 0.11 0.04; KruskalWallisstatistics 0.56 and 0.002, df 1, P 0.45 and 0.96,respectively). These ndings conrmed that naturalenemies would disperse short distances in search ofscale prey.

Influence of Plant Community Structure on Abun-dance and Diversity of Arthropods. Our beating sam-ples of 73 trees yielded 2,887 arthropod specimens of

75 morphospecies. The number of specimens of eachspecies ranged from 1 to 376 individuals, averaging27.4 67.1 specimens per species (mean SD). Thefrequency distribution of the number of specimensper morphospecies was skewed strongly to the right(skewness, 3.81): 18 morphospecies were represented

by only one specimen, nine by two specimens, andeight by three specimens. The remaining 40 mor-phospecies were represented by ve or more individ-uals.

The abundance of all arthropods (the mean numberof individuals collected per sample) was highest inimpoverished habitats (44.1 7.9 individuals per sam-ple), intermediate in turf habitats (29.1 7.2 individ-uals), and lowest in wooded habitats (19.8 2.2 in-dividuals) (F 4.39; df 2, 62; P 0.02; individualmeans signicantly different, LSD test P 0.05). Spe-cies diversity of arthropods in impoverished habitats

(H 2.51), however, was 5% lower than in turfhabitats (H 2.65; t-test P 0.0005) and 20% lowerthan in wooded habitats (H 3.13; t-test P 0.0005).Diversity did not differ signicantly between impov-erished and turf habitats (t-test P 0.05).

Phytophagous species (primarily aphids, leafhop-pers, and thrips) were moreabundant in impoverishedhabitats (19.1 3.6 individuals) than in turf (17.4 4.7) and wooded habitats (8.95 1.9), although vari-ability in abundance within habitats resulted in a lackof statistical signicance (F 2.93; df 2, 61; P 0.061). Species diversity of phytophagous species was

lower in impoverished (H 1.37) and turf habitats(H 1.35) than in wooded habitats (H 1.68), butthese differences were also not signicant (t-test P0.05). Abundance of predaceous arthropods (primar-ily harvestmen, ladybird beetles, lacewings, and spi-ders) also did notvary signicantly with habitat (2.0 0.3 individuals in impoverished habitats, 2.7 1.3 inturf habitats, 2.8 0.8 in wooded habitats; F 0.32;df 2, 61; P 0.05), nor did species diversity ofpredators (impoverished H 1.33, turf H 1.41,wooded H 1.54; t-tests P 0.05). Parasitoids (pri-marily braconids, encyrtids, eupelmids, and mymar-

ids) as a group were nearly equally abundant in allhabitats (0.7 0.2 in impoverished habitats, 0.5 0.2in turf habitats, 0.6 0.2 specimens in wooded hab-itats; F 0.24; df 2, 61; P 0.79), although they weresignicantly less diverse in impoverished habitats (H 1.09) and turf habitats (H 0.97) than in woodedhabitats (H 2.01; t-tests P 0.0005 and P 0.0005,respectively).

Potential predators of pine needle scale (harvest-men, earwigs, crickets, neuropteran larvae, coccinel-lids) did not vary signicantly in abundance acrosshabitats (1.12 0.26 individuals in impoverished hab-itats, 0.80 0.30 in turf habitats, 1.92 0.66 in woodedhabitats; F 1.38; df 2, 61; P 0.26), but speciesdiversity was 30% higher in impoverished thanwooded habitats (impoverished H 1.30, wooded H 1.03; t-test P 0.05).

Table 1. Parasitism rates and predation rates of pine needlescale (mean SE) on Scotch pine seedlings placed in three habitats

nParasitism

rate, %Predation

rate 1,a (%)Predation

rate 2,b (%)

Impoverished 25 26 7.7a 42 9.0a 59 9.4aTurf 24 17 3.9b 41 8.6a 52 9.5aWooded 24 1 0.4c 37 5.8a 54 6.4a

a Only scales with obvious evidence of predation.b As in predation rate 1, but including scales that died before

oviposition and were assumed to have been killed by predators.

Fig. 1. Relationship between mean parasitism rate ofpine needlescaleon potted trees placedin threehabitats andthe number of scales on resident pine hosts counted in a3-min search. Best t regression equation: Y 0.13X 6.06,n 22, r2 0.45; P 0.0006.



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Discussion

Higher species diversity of arthropods in woodedhabitats than in impoverished habitats was consistentwith a positive association between arthropod diver-sity and plant species diversity reported for othermanaged and natural systems (Risch 1981, Hanks and

Denno 1993, Yue et al. 1994, Dean and Milton 1995,Shrewsbury 1996). Nevertheless, arthropods (espe-cially phytophagous species) were most abundant inimpoverished habitats, suggesting that their popula-tions were poorly regulated in those habitats, despiteequal abundance of predators and parasitoids acrosshabitats.

Ours is the rst report that pine needle scale isparasitized by Encarsia aurantii, a cosmopolitan spe-cies that attacks 20 species of armored scale insects(Krombein et al. 1979). Aphytis chilensis, however, isa known parasitoid of C. pinifoliae, C. heterophyllae,

and two other scale species (Krombein et al. 1979,Burden and Hart 1993) and is cosmopolitan (DeBachand Rosen 1991). Aphytis chilensis may represent acomplex of sibling species (Krombein et al. 1979).Coccobius varicornis is also a known parasitoid of C.pinifoliae and C. heterophyllae and nine other speciesof scale insects, and is native to eastern North America(Krombein et al. 1979, Burden and Hart 1993).

It is unlikely that variation in the abundance of pineneedle scale across habitats was related to host plantquality: armored scales have higher survivorship onunstressed hosts (Cockeld and Potter 1986, Hanks

and Denno 1993), but pine needle scale was mostabundant in impoverished, unnatural habitats wheretrees were likely subjected to environmental stress(e.g., Krizek and Dubik 1987, Clark and Kjelgren 1989,Cregg 1995). This apparent paradox may be explainedin part by the lack of effective natural enemies of pineneedle scale in impoverished areas; scale populationsreached high densities even though host quality wassuboptimal.

Higher parasitism rates of pine needle scale in im-poverished habitats, where the scale was most abun-dant, suggest that aphelinids do not effectively regu-

late scale populations in urban habitats as has beenobserved in anotherarmoredscale species (Hanks andDenno 1993). The small size and short life span ofaphelinids presumably limit their ability to y longdistances in search of hosts (Viggiani 1984); they mayprefer to remain in proximity to pines infested with thescale, rather than dispersing. Nevertheless, the waspsreadily traveled the 30 cm from infested trees to par-asitize scales on potted trees, demonstrating that theydo disperse short distances. Dispersal also explainshigher rates of parasitism on potted trees positionednear resident trees that supported high-density scale

populations (Fig 1). Rates of parasitism in woodedhabitats were low, suggesting that parasitoids werescarce in these habitats. Though there is a possibilitythat our excluders hindered parasitoids, parasitismrates were also low in the same habitat when scaleswere on potted trees without screen.

Rates of predation also were similar across habitats.However, we may have underestimated the impact ofpredators on pine needle scale populations becausescales on our potted pine trees were available to pred-ators for only a short time, whereas those on residentpines were exposed their entire lives, providing thepredator guild a greater opportunity to respond tochanges in scale density. Moreover, we did not assesspredation rate in the rst instar, and this source ofmortality may greatly inuence population dynamicsof scale insects (Yang and Sadof 1995, Eliason andMcCullough 1997). We also may not have detecteddifferences between habitats in the abundances ofpredators because of limitations in our sampling meth-ods; we sampled arthropods only from host plants ofpine needle scale and so did not evaluate abundanceof important generalist predators on other plant spe-cies. For example, plant species other than the hostplant are the source of highly mobile predators of

azalea lacebug, Stephanitis pyrioides (Scott) (P.Shrewsbury, personal communication).

The rarity of pine needle scale in wooded habitatssuggests that this pest might be managed in ornamen-tal landscapes by manipulating plant species diversityand structural complexity to foster natural enemies.For example, the parasitoidA. chilensis feeds on pollenof white clover (Trifolium repens L.) and is attractedto its oral volatiles (Tooker 1999); planting whiteclover, or other plant species that provide oral re-sources, in plantations of Christmas trees or in orna-mental landscapes may encourage A. chilensis to sup-

press scale populations. Augmentation of plantdiversity in these habitats also will favor predators byproviding a greater diversity and abundance of alter-native prey and suitable microhabitats.

Acknowledgments

We thank May Berenbaum, Robert Wiedenmann, CliffSadof, Paula Shrewsbury, Eileen Eliason, and an anonymousreviewer. We are grateful for help and research assistanceprovided by Charlie Helm, Art Zangerl, and Megan Weaver.Thanks also to Hensler Nurseries for donating pine seedlings

and to Dave Clark of Hoot Owl Tree Farm, Charles Wilsonof Wilson Tree Farm, and the management of MarketplaceMall and Good Vibes for use of their property. We thankMichael Schauff (USDA Systematic Entomology Labora-tory) and John Heraty (University of California, Riverside)for identifying parasitoid species. This work was in partialfulllment of a M.S. degree for J.F.T. from the University ofIllinois at Urbana-Champaign and was supported in part byUSDA NRI Grant No. 99-353167850 to L.M.H.

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Received for publication 12 May 2000; accepted 11 Septem-ber 2000.


tooker and hanks influence plant community structure natural enemies pine needle scale (homoptera...

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