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Parasitoids and Dipteran Predators Exploit Volatiles from

Microbial Symbionts to Locate Bark Beetles

Author(s): Celia K. Boone, Diana L. Six, Yanbing Zheng, and Kenneth F. Raffa

Source: Environmental Entomology, 37(1):150-161. 2008.

Published By: Entomological Society of America

DOI: http://dx.doi.org/10.1603/0046-225X(2008)37[150:PADPEV]2.0.CO;2

URL: http://www.bioone.org/doi/full/10.1603/0046-225X%282008%2937%5B150%3APADPEV%5D2.0.CO%3B2

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BIOLOGICALCONTROLPARASITOIDS ANDPREDATORS

Parasitoids and Dipteran Predators Exploit Volatiles from MicrobialSymbionts to Locate Bark Beetles

CELIA K. BOONE,

1

DIANA L. SIX,

2

YANBING ZHENG,

3AND

KENNETH F. RAFFA

1,4

Environ. Entomol. 37(1): 150161 (2008)

ABSTRACT Host location by parasitoids anddipteran predators of bark beetles is poorlyunderstood.Unlike coleopteran predators that locate prey by orienting to prey pheromones, wasps and ies oftenattack life stages not present until after pheromone production ceases. Bark beetles have importantmicrobial symbionts, which could provide sources of cues. We tested host trees, trees colonized bybeetles and symbionts, and trees colonized by symbionts alone for attractiveness to hymenopteranparasitoids and dipteran predators. Field studies were conducted with Ips pini in Montana. Threepteromalid wasps were predominant. All were associated with the second and third instars ofI. pini.

Heydenia unica was more attracted to logs colonized by either I. pini or the fungus Ophiostoma ips thanlogs alone or blank controls (screen with no log). Rhopalicus pulchripennis was more attracted to logscolonized byI. pinithan logs alone or blank controls.Dibrachys cavuswas attracted to logs but didnot distinguish whether or not they were colonized. Two dolichopodid predators were predominant.A Medetera species was more attracted to colonized than uncolonized logs and more attracted to logsthan blank controls. It was also more attracted to logs colonized with the yeast Pichia scolyti thanuncolonized logs, but attraction was less consistent. An unidentied dolichopodid was more attractedto logs colonized with I. pini, O. ips, and the bacteriaBurkholderia sp., than to uncolonized logs. It wasalso attracted to uncolonized logs. Its responses were less consistent and pronounced than H. unica.These results suggest some parasitoids and dipteran predators exploit microbial symbionts of barkbeetles to locate hosts. Overall, specialists showed strong attraction to fungal cues, whereas generalistswere more attracted by plant volatiles. These results also show how microbial symbionts can have

conicting effects on host tness.

KEYWORDS Ipspini, parasitoid behavior, predator behavior, microbe interactions, semiochemicals

Bark beetles (Coleoptera: Curculionidae, Scolytinae)are subcorticolous herbivores that spend most of theirlife cycle in the phloem tissues of trees. Some speciesintermittently undergo large-scale population erup-tions with signicant ecological and economical im-pacts. For example, the mountain pine beetle (Den-droctonus ponderosae Hopkins) has killed8.5 million

ha of lodgepole pine during the current outbreak inBritish Columbia (Safranyik and Carroll 2006). Envi-ronmental impacts of bark beetles are complex andcan include alterations in forest structure, wildlifehabitat, andsuccession (Franklin et al. 1987, Matsuokaet al. 2001, McMillin and Allen 2003).

Bark beetles have complex relationships with mi-crobial associates. These relationships vary in degreeof specicity, evolutionary history, consistency of as-

sociation, and functional role (Six and Paine 1999, Six2003, Hofstetter et al. 2005). Some fungi contribute tobeetle nutrition by concentrating nitrogen in thephloem (Goldhammer et al. 1990, Six and Paine 1998,Ayres et al. 2000) or providing a source of sterols(BentzandSix2006). Othersmayenhancethebeetlesability to colonize living trees by assisting in overcom-

ing their defenses (Solheim et al. 1993, Salle et al.2005) or contributing to pheromone production(Brand et al. 1976).

A diversity of bacteria and yeasts are also associatedwith bark beetles, both in their guts (Delalibera et al.2005, Vasanthakumar et al. 2006) and on their exoskel-etons (Six and Paine 1998, Lim et al. 2005). Effects ofthese symbionts on host beetles are largely unstudied,but some may assist in pheromone synthesis (Brand etal. 1975), nutrition (Hodges et al. 1968, Coppedge etal. 1995), or protection from antagonistic fungi (Car-doza et al. 2006).

Microorganisms, including fungi, are known to pro-duce a wide range of volatiles. Attraction to fungalvolatiles is widespread among insects, includingDiptera, Coleoptera, Collembola, Hymenoptera, andLepidoptera, and occurs in a diversity of habitats suchas trees, soil, and decaying organisms (Vet 1983, Bel-

1 Department of Entomology, University of Wisconsin, Madison,WI 53706.

2 Department of Ecosystem and Conservation Sciences, Universityof Montana, Missoula, MT 59812.

3 Department of Statistics, University of Wisconsin, Madison, WI53706.

4 Kenneth F. Raffa, University of WisconsinMadison, Departmentof Entomology, 1630 Linden Dr., Madison, WI 53706 (e-mail:[email protected]).

0046-225X/08/01500161$04.00/0 2008 Entomological Society of America

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ment 3 (control) consisted of an empty aluminumscreen.

Trap Design. The trap stand was a 2-m-long 1.3-cm-diameter aluminum electrical conduit. Holes weredrilled at right angles 5 cm from the top. Two 15-cmlengths of copper wire (6 awg) inserted through theholes provided support for treatment logs and sticky

traps. Each conduit was inserted into a 2.0-cm-diam-eter support conduit in the ground, and the treatmentwas placed on the stand. Sticky traps consisted of33-cm-long by 31-cm-wide pieces of aluminum hard-ware cloth (mesh size, 30 mm) coated with TangleTrap. Each trap was wrapped around a screened treat-ment log, or in the case of a control, formed into acylinder of the same size. The ends of the stickyscreens were bound with small binder clips and se-cured to the copper wire supports with wire (22gauge) and 4-cm alligator clips.

Experimental Design and Sampling Procedure.

Treatments were deployed in a randomized completeblock design (RCBD) consisting of three sites withfour blocks per site. Sites were established near areaswith recent harvesting activities, considerable loggingslash, and detectable populations ofI. pini and naturalenemies. Traps were arranged with 10 m betweentreatments, 100 m between blocks, and at least 500 mbetween sites. Sticky traps were collected and re-placed with clean traps at 4-d intervals until adultsemerged from logs in treatment 1. Treatments werererandomized at each collection period.

Insects were removed from sticky traps with a nepaint brush (Size 0) dipped in 100% Citrisolv to re-move Tangle Trap and stored in 100% Citrisolv in15-ml vials until identication. Hymenoptera andDiptera were identied using the following keys: Gra-ham (1969), Krombein et al. (1979), McAlpine et al.(1981), andBickel (1985). Taxonomicverication wasperformed by various experts identied in the ac-knowledgments. Voucher specimens of parasitoidswere deposited at the UWMadison Department ofEntomology Insect Research Collection.

Isolation and Identification of Microbes Associatedwith Beetle Stages. A parallel set of logs with the sametreatments outlined in experiment 1 was deployed

70 m from one study site. Subsamples were destruc-tively sampled weekly from 29 May to 2 July (gener-ation 1) and 24 July to 19 August (generation 2). Thenumber of beetles in each developmental stage wasrecorded. Microbial samples were collected by streak-ing parental adults, eggs, larvae, pupae (or pupalchamber), and teneral adults across 2% malt extractagar (MEA). Boring dust (adult frass), larval frass, andphloem (4-mm cores) were also taken from tips ofbrood and parental adult galleries and egg niches andcultured individually onto MEA.

Isolates were stored at 23C under natural light

(15.5 L:8.5 D) for at least 10 d and visually inspectedfor the presence of fungi. By 10 d, cultures had begunto produce spores that aid in identication. Culturesthat were not identied soon after 10 d were stored ina refrigerator until identications could be made.Ophiostomaspecies were identied directly from ini-

tial isolationsusingmorphological characteristics (Up-adhyay 1981, Grylls and Seifert 1993) and DNA ex-traction and sequencing. For Ophiostoma, polymerasechain reaction (PCR) was performed using Bt2b andT10 primers to amplifya portion of the-tubulin gene.PCR products were sequenced on an ABI 3130X2automated sequencer (Perkin-Elmer, Walthan, MA)

at the Murdock Sequencing Facility at the Universityof Montana, Missoula, MT. Sequences were comparedwith sequences in the Sequence Match utility of Gen-Bank using BLAST searches (http://ncbi.nlm.nih-.gov/BLAST) to determine the closest match.

Yeasts and bacteria were puried from initial iso-lates by dilution plating. A starting suspension wasmade by streaking a probe across the surface of anisolation plate and then swirling the probe in 1.0 mlsterile water. The suspension was vortexed briey.Dilutions of 101, 102, 103, and 104 of the originalsuspension were spread across the surface of MEA in

30 petri dishes and assessed for the growth of coloniesafter 24, 48, and 120 h. For each initial isolation, therelative prevalence of microbes was assessed from thedilution plate yielding the most distinct, nonoverlap-ping colonies after 48 h. Colonies in each plate werecoded by morphology and counted. Pure cultures ofthe two most prevalent morphotypes over all isola-tions were produced using streak plates. The purecultures were used for DNA extraction and sequenc-ing. One of the two most common colony morpho-types was a bacterium. The partial 16S rRNA gene ofthisbacterium wasamplied using thegeneral primers536f and 907r and PCR performed as in Holben et al.(2002). The Sequence Match utility of RDP II releasenine (http://rdp.cme.msu.edu/) (Maidak et al. 1997)was used to determine the closest known relative. Thesecond most common morphotype was a yeast. Its ITSregion of rDNA was amplied using the primersITS1-F and ITS4. The resulting sequence was com-pared with sequences in the Sequence Match utility ofGenBank using BLASTsearches (http://ncbi.nlm.nih.gov/BLAST) to determine the closest match.

Experiment 2

Experiment 2 tested whether natural enemies are at-tractedto thepredominantmicrobial symbionts ofI. piniobtainedinexperiment 1.Itwas conducted onceforeachgeneration in 2003, with sampling periods of 17 June to3 August and 428 August. Fivehealthy trees werefelledand prepared as described in experiment 1.

Based on results of isolations from parallel logs inexperiment 1, the treatments during the rst ightwere as follows: (1) blank control; (2) log alone; (3)log naturally infested withI. piniand its natural com-plement of microbes; (4) log inoculated withOphios-toma ips (Rumbold) Nanff; (5) log inoculated with

Burkholderia sp.; (6) log inoculated with Pichia scolyti(Phaff and Yoneyama); and (7) log with introduced I.piniadults. The same treatments were tested in gen-eration 2, except treatment 7 was replaced with a logcontaining all three of the predominant microbes, O.ips, Burkholderia sp., and P. scolyti (six inoculation

152 ENVIRONMENTALENTOMOLOGY Vol. 37, no. 1

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points each). Because we had inadequate numbers ofadults in generation 1 to articially infest logs, we usednaturally infested trees containing L2L3 larvae fortreatment 3. No other insects were observed in theselogs. The experimental design consisted of three siteswith three blocks per site for generation 1 and threesites and four blocks per site for generation 2.

Actively growing (10 d) cultures on 2% MEA wereused for the treatments receiving microbes. The barkwas smoothed slightly with a drawshave and sprayed

with 70% ethanol. Sixteen evenly spaced 0.6-cm holeswere drilled using a sterilized (70% ethanol) drill bit.A 0.6-cm-diameter plug of agar supporting a microbialculture was inserted into each hole using sterile for-ceps, the bark plug was replaced, and the hole wassealed with inert silicone sealant. Treatment 2 (inoc-ulated control) received agar plugs but no microbes.

Statistical Analyses

Trap-catch data were analyzed as a nested block de-sign tted with a Poisson regression using the function

glmmPQL in the statistical package R (Ihaka and Gen-tleman 1996). The site effect was not signicant, so datawere pooled across sites, analyzed according to RCBDusing the glm function, and followed by mean contrasts.In 2002, the parasitoid data contained many zeros, re-sulting in numerical instability in R, so counts were ag-

gregated within sites across blocks for each treatmentand analyzed according to RCBD tted with a Poissonregression using the genmod procedure in SAS (SASInstitute2003).Becauseofstrong temporalpatterns(seeResults), behavioral analyses of parasitoids were re-stricted to periods when they were abundant to avoidheteroskedascity caused by excessive zeroes: H. unicageneration 1, L2;R. pulchripennisgeneration 1, L2;D.cavusgeneration 1, adults, generation 2, egg-L1. ForMedeterasp. and the unidentied dolichopodid, gener-

ation effects were not signicant, so mean contrasts oftreatment effects were performed on the pooled data ofboth generations. Experiment 2 was analyzed as in ex-periment 1. To account for unbalanced treatments be-tween the rst and second generations, data were rstpooled by generation to compare treatments effectsamong allseven treatmentsin each generation. The datafor both generations were pooled for comparisonsamong the rst six treatments only.

Results

Abundance and Seasonal Phenology of Parasitoidsand Dipteran Predators and Their Association withI. piniLife Stages

The most common bark beetle parasitoids in 2002were the pteromalidsHeydenia unicaCook and Davis

0

5

10

15

20-Jun

30-Jun

10-Jul

20-Jul

30-Jul

9-Au

g

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70

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29-Jun

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31-Jul

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g

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Totalno.

sp.

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250Totalno.unidentifieddolichopodid

Medetera sp. Unidentified dolichopodid

0

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60

24-May

1-Ju

n

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n

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25-Jun

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g

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22-Aug

0

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300Totalno.unidentified

dolichopodid

Medetera s p. Unidenti fied dol ic hopodid

d.

b.

Dipteran predators

2003

c.

H.unic

a

Totalno.Medeterasp.



d.c.

Totalno.

sp.

Parasitoids

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02

a.

0

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23-M

ay

2-Ju

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12-J

un

22-J

un2-

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12-J

ul

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11-A

ug

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ug

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parasitoids

H. unica R. pulchripennis D. cavus

20

M

edetera

0

10

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30

40

23-M

ay

2-Ju

n

12-J

un

22-J

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22-J

ul

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ug

21-A

ug

31-A

ug

H. unicaH. unica R. pulchripennis D. cavus

Fig. 1. Seasonal abundance of hymenopteran parasitoids and dipteran predators arriving at traps containing various log,

beetle, and symbiont treatments in western Montana during 2002 and 2003.

February 2008 BOONE ET AL.: MICROBIALATTRACTION OFNATURALENEMIES 153

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(46), Rhopalicus pulchripennis Crawford (41), and Di-brachys cavus Walker (51). Most H. unica (84.8%)were captured during the rst generation (20 May to15 July; peak, 1115 July; Fig. 1). Similarly, 75.6% ofR.pulchripenniswere caught during the rst generation(peak, 1115 July). D. cavus were more evenly dis-tributed, with 47.1% captured in the rst generationand 52.9% in the second generation. Captures peakedduring 2125 June and 2529 July. In 2003, the mostabundant parasitoid was H. unica (107). No otherspecies, includingR. pulchripennisandD.cavus,werecaught in appreciable numbers (40 individuals).

Themost common predators in 2002 were Dolichopo-didae (2,256), consisting of 19.6% Medetera sp. (448) and81.4% of an unidentied dolichopodid (1,808) (Fig. 1).PeakcapturesofMedetera sp.occurred1115 July duringI. pinis rst generation (11.6%), and 1014 August dur-ing the second (6.3%). Peak capturesof the unidentieddolichopodid occurred 2125 July (5.1%)during therstgenerationand1014 August (13.2%) duringthe secondgeneration. In 2003, 3,558 dolichopodids were captured,consisting of the same Medetera sp. (20.6%) and uniden-tied dolichopodid (79.4%) as in 2002. Peak captures ofH. unica and the unidentied dolichopodid occurred

2731 July, and peak captures ofMedeterasp. occurred2529June. Duringthesecondgeneration,peakcapturesof bothMedeterasp. (14.2%) and the unidentied doli-chopodid (16.5%) occurred 48 August.

In 2002, I. pini larvae were present beginning 17June during the rst generation and from 31 July to 19August during the second generation (Table 1). Dur-

ing the second generation, the eggL1 stages ofI. piniwere present from 31 July to 12 August. The L2adultstages were present from 13 to 28 August. The extentsto which various natural enemies were associated withI. pinis generations and life stages are shown in Table2. Nearly all H. unica and R. pulchripennis were caughtafter theL1 stage. In contrast, theseasonal distribution

ofD. cavus mostly overlapped L2adult ofI. pinis rstgeneration and eggL1 ofI. pinis second generation.As with the hymenopteran parasitoids, dipteran pred-ators were primarily associated with L2 and later(79.3% for Medetera sp. and 60.7% for the unidentieddolichopodid).

In 2003, I. pini L2adults were present from 17 Juneto 31 July in the rst generation (Table 3). During thistime, 85.1% of H. unica, 65.0% of Medetera sp., and62.6% of theunidentied dolichopodidwere captured.Ips pinis eggL1 stages were present from 31 July to12 August, and L2adults were present from 13 to 28

August during the second generation. During the L2adult stages, Medetera sp. comprised 20.8% and theunidentied dolichopodid comprised 20.9% of the to-tal dipteran predators captured.

Isolation and Identification of Microbes Associatedwith Beetle Stages

Three microorganisms were consistently isolatedfrom theP. ponderosalogs colonized byI. pini. O. ipswas the most common associate ofI. pini adults, beingisolated from 89.7% of insects in the rst generation

and 85.7% of insects in the second generation. Theyeast, Pichiascolyti (Phaff and Yoneyama; 100%matchto AY761155 in GenBank), and the bacterium Burk-holderia sp. (95.4% match to AJ292641 in GenBank)often co-occurred with O. ips, but were not consis-tently associated with any specic I. pini developmen-tal stages.

Natural Enemy Responses to Sources of VolatilesAssociated withI. pini

Experiment 1: Plant Material With or Without I.

pini. There were signicantsourcesof attraction forallthree wasp species(Fig. 2a).Captures ofH. unica werehigher on I. pini--colonized logs than either uncolo-nized logs (P 0.0375) or blank controls (P 0.0001)and on uncolonized logs than blank controls (P0.0001). R. pulchripennis captures were also signi-cantly higher on colonized logs than uncolonized logs

Table 1. Seasonal phenology ofI. pinicolonizingP. ponderosa

logs in western Montana, 2002

Generation 1 29 May 11 June 17 June 25 June 2 July

Egg 100 (5) 100 (31) 36 (19) 0 0Larvae: L1 0 0 25 (13) 0 0Larvae: L2 0 0 39 (20) 100 (89) 165 (15)Larvae: L3 0 0 0 0 84 (81)

Generation 2 24 July 31 July 6 Aug. 13 Aug. 19 Aug.

Egg 100 (55) 29 (10) 0 0 0Larvae: L1 0 71 (25) 0 3 (2) 0Larvae: L2 0 0 33 (17) 0 0Larvae: L3 0 0 67 (34) 65 (39) 3 (2)Prepupae 0 0 0 3 (2) 2 (1)Pupae 0 0 0 24 (14) 7 (4)Adult: Teneral 0 0 0 5 (3) 85 (52)Adult: Mature 0 0 0 0 3 (2)

Data represent percentage (N) associated with each stage. Gen-eration 1: logs deployed 20 May; generation 2, logs deployed 17 July.

Table 2. Percentage (N) of hymenopteran parasitoids and dipteran predators associated with various life stages ofI. pini in western

Montana during 2002

Generation Stage Dates

Hymenopteran parasitoids Dipteran predators

H. unica R.pulchripennis D. cavus Medeterasp. Unidentieddolichopodid

1 EggL1 20 May to 13 June 2.2 (1) 0 2.0 (1) 1.3 (6) 0.01 (1)L2adult 14 June to 15 July 82.6 (38) 75.6 (31) 45.1 (23) 54.7 (245) 13.5 (244)

2 EggL1 17 July to 2 Aug. 0 0 37.2 (19) 19.4 (87) 39.3 (711)L2adult 226 Aug. 15.2 (7) 24.4 (10) 15.7 (8) 24.6 (110) 47.2 (852)


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(P 0.0001) or blank controls (P 0.0001). Theywere also attracted to uncolonized logs but onlyweakly (P 0.0414). D. cavuscaptures were higher onboth colonized (P 0.0001) and uncolonized logs(P 0.0085) than blank controls. However,D. cavusdid not distinguish between colonized and uncolo-nized logs (P 0.05).

Logs colonized by I. piniattracted more Medetera

sp. than did uncolonized logs (P 0.0001) and blank

controls (P 0.0001), and uncolonized logs attractedmore than blank controls (P 0.0415; Fig. 2b). Un-colonized logs attracted more of the unidentied doli-chopodid than colonized logs (P 0.0001) or blankcontrols (P 0.0001). However, colonized logs at-tracted more of this dolichopodid than did blank con-trols (P 0.0001).

Experiment 2: Microorganisms.Logs colonized by

L2L3 I. pini or the fungus O. ips were more attractive

b.

a

bc

a

b

c

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Medeterasp. Unidentified dolichopodid

Meanno.

dipteranpredators+SE

Log + I. pini Log Control

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c c

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a

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H. unica R. pulchripennis D. cavus

Meanno.parasitoids+SE

Log + I. pini Log Control

a.

a

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c c

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a

a

a

0

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15

Fig. 2. Response (mean SE) of (a) hymenopteran parasitoids and (b) dipteran predators to P. ponderosa andP.ponderosa colonized byI. pini in western Montana. Means with the same letter are not signicantly different at P 0.05.

Table 3. Percentage (N) ofH. unica, Medetera sp. andan unknown dolichopodidassociated with various life stages ofI. piniin western

Montana during 2003

Generation Stage Dates H. unica Medeterasp. Unidentied

dolichopodid

1 EggL1 NA NA NA NAL2adult 17 June to 31 July 85.1 (91) 65.0 (234) 62.6 (870)

2 EggL1 31 July to 12 Aug. 2.8 (3) 14.2 (51) 16.5 (230)

L2adult 1328 Aug. 12.1 (13) 20.8 (75) 20.9 (290)

NA, not applicable.


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to H. unica than any other treatment (Fig. 3), with theexception that the O. ips and Burkholderia sp. treat-ments were not statistically different. Arrival by H.unica was equivalent to logs colonized by L2L3 I. piniandO. ips.Logs colonized withO. ipscaught moreH.unicathan did logs alone (P 0.0001) or blank con-trols (P 0.0003). Captures on logs colonized withBurkholderia sp. were higher than on blank controlsbut did not differ from uncolonized logs. Logs colo-nized withP. scolytior I. pini adults did not capturemoreH. unicathan either uncolonized logs or blankcontrols.

Overall, logs colonized by P. scolyti caught moreMedetera sp. than uncolonized logs (P 0.0377) orblank controls (P 0.0001; Fig. 4a). No other treat-ments were more attractive than logs alone.Medeterasp. wasmore attracted to alltreatmentscontaining logsthan blank controls (P 0.05). However, responsesvaried among experiments associated with the twogenerations ofI. pini (Fig. 4, b and c).

Overall, logs colonized by I. pini (all stages), O. ips,

andBurkholderiasp. were more attractive to the un-identied dolichopodid than uncolonized logs or con-trols (Fig. 5a). This species was also more attracted toall treatments containing logs than blank controls dur-ing both generations ofI. pini(P 0.05; Fig. 5, b andc). Like Medetera sp., however, responses by this yvaried between experiments.

Discussion

These results support the hypotheses that someparasitoids and dipteran predators locate bark beetles

by orienting to volatile cues associated with host de-velopment (Sullivan et al. 1997, 2000, Pettersson et al.2001), and in particular, that some species are at-tracted to volatiles emitted by the beetles fungal sym-bionts (Sullivan and Berisford 2004). Different para-sitoid species vary in their behaviors. For example,H.

unica andR. pulchripennis are more attracted to I.pinicolonized plant tissue than uncolonized planttissue. Moreover, the arrival ofH. unica at colonizedlogs can beexplained largely by attractiontocues frommicrobial symbionts, especially O. ips. D. cavus is like-wise attracted to ponderosa pine, but in contrast to theother wasps, its attraction is not increased by I. pinicolonization. The identities of the attractive volatilesare unknown, but work with Rhopalicus tutela(Walker) suggests that oxygenated monoterpenes,such as those released by I. typographusinfested trees,are involved (Pettersson 2001, Pettersson and Boland2003). Consistent with the role of fungi in parasitoidattraction, ophiostomatoids metabolize terpenoidcompounds (Hanssen 1993).

Like the parasitoids, some dipteran predators wereattracted to volatilesassociated with host plants; plantscolonized byI. piniand its microbial symbionts.Me-detera sp. and the unidentied dolichopodid weremore attracted to plant tissue, and each showed someadditional attraction to logs colonized by fungi. How-

ever, their responses were less consistent and pro-nounced than those ofH. unica.

Overall, the stronger attraction ofH. unicaandR.pulchripennisto I. pinilarvae and/or associated mi-crobes, and the stronger attraction ofD. cavus andpredators to plant volatiles, support the view thatspecialist natural enemies exploit more explicit in-fochemicals than generalists (Steidle and van Loom2003). For example, the host range of H. unica islimited to bark beetles in Dendroctonus, Ips, Scoly-tus, Phloesinus, and Polygraphus (Krombein et al.1979). Most, if not all, species in these genera are

associated withOphiostomaor closely related fungi(Paine et al. 1997). Thus, volatiles from these fungicombined with tree compounds such as -pinene(Camors and Payne 1972) may provide a reliablesignal for detecting hosts. Furthermore, H. unicaseems to be highly specialized on a particular stage

0

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rol

Log

I.pini

(Lar

vae)

O.ips

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lderia

sp.

P.sco

lyti

I.pini

(Adu

lts)

Meanno.

H.unica+SE

d

cd

a

ab

bc

cd

d

Fig. 3. Response (mean SE) ofH. unica to P. ponderosa, P. ponderosa colonized by I. pini, P. ponderosa inoculated with

microbial symbionts, and blank controls. Experiments conducted during the L2-adults stages ofI. pinis rst generation (17June to 3 August). Means with the same letter are not signicantly different at P 0.05. Treatments containingI. piniwereadministered either as logs infested with larvae or logs exposed to adults that subsequently produced brood.


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of development. For example, 84% ofH. unica ar-

riving at trees colonized by D. frontalis were asso-ciated with third-instar larvae (Camors and Payne1972), similar to our observations that they aremostly associated with later developmental stages ofI. pini (Table 2). Likewise, although R. pulchripennisparasitizes many bark beetle species, it is limited to

the Scolytinae. It showed the highest relative at-

traction to colonized versus uncolonized tissue, al-though there were insufcient numbers in 2003 totest whether this was caused by microorganisms. Incontrast, D. cavus is polyphagous, attacking manyinsect orders and spiders (Graham 1969, Krombeinet al. 1979). Similarly, most dolichopodids are rel-

0

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rol

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I.pini

O.ips sp

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d

bc bc

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abab

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c. Generation 2

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)

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yti

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bine

dm

icrob

es

a

bc

c

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ab

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0

2

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rol

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I.pini

(Lar

vae)

O.ips

Burkho

lderia

sp.

P.sco

lyti

I.pini

(Adu

lts)

Meanno.

Medeterasp

.+SE

0

2

4

6

8

Burkho

lderia

a

Fig. 4. Response (mean SE) ofMedetera sp. to P. ponderosa, P. ponderosa colonized by I. pini, P. ponderosainoculated with microbial symbionts, and blank controls (a) pooled acrossI. pinis generations, (b) generation 1, and(c) generation 2. Means with the same letter are not signicantly different at P 0.05. Treatments containing I. piniwere administered either as logs infested with larvae, logs exposed to adults that subsequently produced brood, or bothtechniques (data pooled).


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atively generalist predators or scavengers and occurin diverse habitats (Coulibaly 1993).

The numbers of known parasitoids of bark beetlesobtained in this study were quite low, being only 2%that of our captures of predaceous ies. Consistentlymore predators than parasitoids ofI. pini are capturedin the eld, regardless of region or the trappingmethod used (Raffa and Dahlsten 1995, Aukema et al.

2000, Dahlsten et al. 2004). Furthermore, studies withNorth American and European bark beetles have

shown relatively low mortality attributable to parasi-toids (Amman 1984, Weslien and Schroeder 1999,Hougardy and Gregoire 2001, Feicht 2006). Overall,these results suggest that parasitoids are probably in-sufcient to exert much population regulation or se-lective pressure onI. piniunder natural conditions.

0

5

10

15

C

ontro

lLo

g

I.pini(

Adul

ts)

O.ips

Burkhold

eria

sp.

P.sc

olyti

Com

bine

dmic

robe

s

c. Generation 2

b

ab

a

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b

ab

d

b. Generation 1

ab ab

bc bc

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c

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sp.

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Meanno.unidentifieddolichopodid+SE

c

b

aa

ab

a. Pooled a

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rol

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I.pini

O.ips sp

.

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lyti

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ontro

lLo

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I.pini(

Adul

ts)

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Burkhold

eria

sp.

P.sc

olyti

Com

bine

dmic

robe

s

b

ab

a

ab

c

b

ab

d

b. Generation 1

ab ab

bc bc

ab

c

0

10

20

30

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rol

Log

I.pini

(Lar

vae)

O.ips

Burkho

lderia

sp.

P.sco

lyti

I.pini

(Adu

lts)

c

b

aa

ab

a

Cont

rol

Log

I.pini

O.ips

Burkho

lderia

sp.

P.sco

lyti

Fig. 5. Response (mean SE) of the unidentied dolichopodid toP. ponderosa, P. ponderosa colonized byI. pini, P.ponderosainoculated with microbial symbionts, and blank controls (a) pooled acrossI. pinis generations, (b) generation 1,and (c) generation 2. Means with the same letter are not signicantly different at P 0.05. Treatments containing I. pini wereadministered either as logs infested with larvae, logs exposed to adults that subsequently produced brood, or both techniques(data pooled).


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These results add to our understanding of how mi-crobial associates of bark beetles can have multipleand varying effects on their vectors (Klepzig and Six2004, Kopper et al. 2004). For example, O. ips canincrease I. pini brood production (Kopper et al. 2004),butcanalso have an indirect negative effect on itshostby attracting natural enemies. From the natural ene-

mys perspective,O. ipsoffers the most reliable signalofI. pinilarvae, because it is the most frequent asso-ciate, is present with host larvae, and occurs in all, oralmost all, trees colonized by I. pini (Klepzig et al.1991). The amount and location of the host tree thatmicroorganisms colonize may inuence the strengthsand roles of their signals. For example, O. ips oftencolonizes almost all of the phloem and much of thesapwood, whereas bacteria and yeast often occupyonly restricted microhabitats along the beetles gal-lery. Thus, O. ips may producea strongersignal and beimportant in long distance host location, whereas bac-

teria and yeast may be more important in short dis-tance location.

Acknowledgments

The assistance of the staff of Lubrecht Experimental For-est, University of Montana, especially H. Goetz and F. Maus,is deeply appreciated. M. Phau, C. Paterson, T. Benson (De-partment of EcosystemandConservationScience, Universityof Montana, Missoula, MT), and K. Kieler (Department ofEntomology, UW, Madison, WI) provided technical assis-tance. S. Krauth (Department of Entomology, UW, Madison,

WI), E. Grissel, USDA Research Entomologist, U.S. Museumof Natural History, Smithsonian Institute (Pteromalidae); J.Luhman, Biological Control Scientist and Adjunct AssistantProfessor, University of Minnesota, Department of Entomol-ogy (Braconidae); M. W. Gates, USDA Systematic Entomol-ogy Research Scientist, Smithsonian Institute (Eulophidae);and M. Yoder, PhD Candidate, Texas A&M University, De-partment of Entomology (Diapriidae), assisted with insectidentication. We thank S. Adams (Division of BiologicalServices, University of Montana, Missoula, MT) for identi-fying the bacterial isolate used in this project. J. Zhu (De-partment of Statistics, UWMadison, Madison, WI) providedstatistical advice. We thank the anonymous reviewers forhelpful critiques of this paper. This work was supported by

USDA NRI (2003-3502-13528), the National Science Foun-dation (DEB0314215), and UWMadison College of Agri-cultural and Life Sciences.

References Cited

Amman, G. D. 1984. Mountain pine beetle (Coleoptera:Scolytidae) mortality in three types of infestations (Den-droctonus ponderosae, Pinus contorta). Environ. Entomol.13: 184 191.

Aukema, B. H., D. L. Dahlsten, and K. F. Raffa. 2000. Ex-ploiting behavioral disparities among predators and preyto selectively remove pests: Maximizing the ratio of barkbeetles to predators removed during semiochemicallybased trap out. Environ. Entomol. 29: 651660.

Ayres, M. P., R. T. Wilkens, J. J. Ruel, M. J. Lombardero, andE. Vallery. 2000. Nitrogen budgets of phloem-feedingbark beetles with and without symbiotic fungi. Ecology81: 21982210.

Belmain, S. R., M.S.J. Simmonds, and W. M. Blaney. 2002.Inuence of odor from wood-decaying fungi on hostselection behavior of deathwatch beetle,Xestobium ru-fovillosum.J. Chem. Ecol. 28: 741754.

Bentz, B. J., and D. L. Six. 2006. Ergosterol content of fungiassociated with Dendroctonus ponderosae andDendroc-tonus rufipennis (Coleoptera: Curculionidae, Scolytinae).

Ann. Entomol. Soc. Am. 99: 189194.Bickel, D. J. 1985. A revision of the Nearctic Medetera(Diptera: Dolichopodidae). USDA Tech. Bull. 1692:1109.

Brand, J. M., J. W. Bracke, A. J. Markovetz, D. L. Wood, andL. E. Browne. 1975. Production of verbenol pheromoneby a bacterium isolated from bark beetles. Nature(Lond.) 254: 136137.

Brand, J. M., J. W. Bracke, L. N. Britton, A. J. Markovetz, andS. J. Barras. 1976. Bark beetle pheromones: productionof verbenone by a mycangial fungus of Dendroctonusfrontalis.J. Chem. Ecol. 2: 195199.

Camors, F. B., and T. L. Payne. 1972. Response ofHeydeniaunica (Hymenoptera: Pteromalidae) to Dendroctonus

frontalis (Coleoptera: Scolytidae) pheromones and ahost-tree terpene. Ann. Entomol. Soc. Am. 65: 3133.

Cardoza, Y. J., K. D. Klepzig, and K. F. Raffa. 2006. Bacteriain oral secretions of an endophytic insect inhibit antag-onistic fungi. Ecol. Entomol. 31: 636645.

Coppedge, B. R., F. M. Stephen, and G. W. Felton. 1995.Variation in female southern pine beetle size and lipidcontent in relation to fungal associates. Can. Entomol.127: 145154.

Coulibaly, B. 1993. Dolichopodidae (Diptera) in the bio-logical control of certain insects harmful to forest eco-systems. Insect Sci. Appl. 14: 8587.

Dahlsten, D. L., D. L. Six, D. L. Rowney, A. B. Lawson, N.Erbilgin, and K. F. Raffa. 2004. Attraction of Ips pini(Coleoptera: Scolytinae) and its predators to natural at-tractants and synthetic semiochemicals in northern Cal-ifornia: Implications for population monitoring. Environ.Entomol. 33: 15541561.

Delalibera, I., J. Handelsman, and K. F. Raffa. 2005. Con-trasts in cellulolytic activities of gut microorganisms be-tween the wood borer, Saperda vestita (Coleoptera:Cerambycidae), and the bark beetles, Ips piniandDen-droctonus frontalis (Coleoptera: Curculionidae). Envi-ron. Entomol. 34: 541547.

DeMoraes, C. M., and M. C. Mescher. 1999. Interactions inentomology: plant-parasitoidinteraction in tritrophic sys-tems. J. Entomol. Sci. 34: 3139.

Dorado, J., F. W. Claassen, T. A. van Beek, G. Lenon, J.B.P.A.Wijnberg, and R. Sierra-Alvarez. 2000. Elimination anddetoxication of softwood extractives by white-rot fungi.J. Biotech. 80: 231240.

Erbilgin, N., E. V. Nordheim, B. H. Aukema, and K. F. Raffa.2002. Population dynamics ofIps pini and Ips grandicollisin red pine plantations in Wisconsin: Within- and be-tween-year associations with predators, competitors, andhabitat quality. Environ. Entomol. 31: 10431051.

Feicht, E. 2006. Frequency, species composition and ef-ciency of Ips typographus (Col., Scolytidae) parasi-toids in infested spruce forests in the National ParkBavarian Forestover three consecutive years. J. PestSci. 79: 3539.

Franklin, J. F., H. H. Shugart, and M. E. Harmon. 1987.Tree death as an ecological process. BioScience 37:550556.

Goldhammer, D. S., F. M. Stephen, and T. D. Paine. 1990.The effect of the fungiCeratocystis minor(Hedgecock)Hunt, var.barrasiiTaylor, and SJB-122 on reproductionof


8/13/2019 Boone 2008

12/13

the southernpinebeetle, Dendroctonus frontalis Zimmer-man (Coleoptera, Scolytidae). Can. Entomol. 122: 407418.

Graham, M.W.R. de V. 1969. The Pteromalidae of north-western Europe (Hymenoptera: Chalcidoidea). BritishMuseum of Natural History, London, UK.

Grylls, B. T., and K. A. Seifert. 1993. A synoptic key to

species ofOphiostoma,andCeratocystiopsis,pp. 261268.InM. J. Wingeld, K. A. Seifert, and J. F. Webber (eds.),Ceratocystis and Ophiostoma: taxonomy, ecology, and pa-thology. APS Press, St. Paul, MN.

Hanssen, H. P. 1993. Volatile metabolites produced by spe-cies ofOphiostomaandCeratocystis,pp. 117126.InM. J.Wingeld, K. A. Seifert, and J. F. Webber (eds.), Cera-tocystisandOphiostoma:taxonomy, ecology, and pathol-ogy. APS Press, St. Paul, MN.

Hodges, J. D., S. J. Barras, and J. K. Maudlin. 1968. Aminoacids in inner bark of loblolly pine as affected by thesouthern pine beetle and associated micro-organisms.Can. J. Bot. 46: 146772.

Hofstetter, R. W., J. B. Mahfouz, K. D. Klepzig, and M. P.

Ayres. 2005. Effects of tree phytochemistry on the in-teractions among endophloedic fungi associated with thesouthern pine beetle. J. Chem. Ecol. 31: 539560.

Holben, W. E., P. Williams, S. M. Saarinen, and J.H.A. Apa-jalhti. 2002. Phylogenetic analysis of intestinal micro-ora indicates a novelMycoplasmaphylotype in farmedand wild salmon. Microbial Ecol. 44: 175185.

Hougardy, E., and J. C. Gregoire. 2001. Bark beetle parasi-toids population surveys followingstem damage in sprucestands in the Vosges region (France). Integr. Pest Man-age. Rev. 6: 163138.

Hulcr, J.,M.Pollet, K. Ubik, and J. Vrkoc. 2005. Exploitationof kairomones and synomones byMedetera spp. (Diptera:Dolichopodidae), predators of spruce bark beetles. Eur.J. Entomol. 102: 655662.

Ihaka, R., and R. Gentleman. 1996. R: a language for dataanalysis and graphics. J. Comput. Graph. Stat. 5: 299 314.

Klepzig, K. D., and D. L. Six. 2004. Bark beetle-fungal sym-biosis: context dependency in complex associations. Sym-biosis 37: 189205.

Klepzig, K. D., K. F. Raffa, and E. B. Smalley. 1991. Asso-ciation of an insect-fungal complex with red pine declinein Wisconsin. For. Sci. 37: 11191139.

Kopper, B. J., K. D. Klepzig, and K. F. Raffa. 2004. Compo-nents of antagonism and mutualism in Ips pini-fungalinteractions: Relationship to a life history of colonizinghighly stressed and dead trees. Environ. Entomol. 33:

2834.Krombein, K. V., P. D. Hurd, P. D. Smith, and B. D. Burks.

1979. Catalogue of Hymenoptera in America North ofMexico. vol. I. Symphyta and Apocrita (Parasitica).Smithsonian Institution Press, Washington, DC.

Lanza, E., and J. K. Palmer. 1977. Biosynthesis of monoter-penes by Ceratocystis moniliformis. Phytochemistry 16:15551560.

Lieutier, F., A. Yart, H. Ye, D. Sauvard, and V. Gallois. 2004.Variations in growth and virulence of Leptographiumwingfieldii Morelet, a fungus associated with the barkbeetle Tomicus piniperda L. Ann. For. Sci. 61: 4553.

Lim, Y. W., J. J. Kim, M. Lu, and C. Breuil. 2005. Deter-mining fungal diversity onDendroctonus ponderosaeand

Ips piniaffecting lodgepole pine using cultural and mo-lecular methods. Fungal Divers. 19: 7994.

Linit, M. J., and F. M. Stephen. 1983. Parasite and predatorcomponent of within tree southern pine beetle (Co-leoptera: Scolytidae) mortality. Can. Entomol. 115: 679688.

Livingston, R. L. 1979. The pine engraver, Ips pini (Say), inIdaho: Life history, habits and management recommen-dations. Idaho Dept. Lands,Forests,Insects, DiseaseCon-ditions Report No. 793.

Madden, J. L. 1968. Behavioral responses of parasites to thesymbiotic fungus associated with Sirex noctilio. Nature(Lond.) 218: 189190.

Maidak, B. L., G. J. Olsen, N. Larsen, R. Overbeek, M. J.McCaughey, and C. R. Woese. 1997. The rdp (ribosomaldatabase project). Nucleic Acids Res. 25: 10911.

Matsuoka, S. M., C. M. Handel, and D. R. Ruthrauff. 2001.Densities of breeding birds and changes in vegetation inan Alaskan boreal forest following a massive disturbanceby spruce beetles. Can. J. Zool. 79: 16781690.

McAlpine, J. F., B. V. Peterson, G. E. Shewell, H. J. Teskey,J. R. Vockeroth, and D. M. Wood. 1981. Manual ofNearctic Diptera. vol. I. Canadian Government Publish-ing Centre, Hull, Quebec.

McMillin, J. D., and K. K. Allen. 2003. Effects of Douglas rbeetle (Coleoptera: Scolytidae) infestations on forestoverstory and understory conditions in western Wyo-

ming. West. N. Am. Nat. 63: 498506.Mills, N. J., K. Kruger, and J. Schlup. 1991. Short-range host

location mechanisms of bark beetle parasitoids. J. Appl.Entomol. 111: 3343.

Mironov, V. A., M. I. Tsibulskaya, and M. T. Yanotovsky.1982. Synthesis of monoterpenes by the ascomyceteEr-emothecium ashbyi. Prikl Biokhim. Mikrobiol. 18: 343345.

Nebeker, T. E. 1989. Bark beetles, natural enemies, man-agement selection interactions, pp. 7180. In D. L. Kul-havy and M. C. Miller (eds.), Potential for biologicalcontrol ofDendroctonusandIps bark beetles. School ofForestry, Stephen F. Austin State University, Nacogdo-ches, TX.

Paine, T. D., K. F. Raffa, and T. C. Harrington. 1997. Inter-actions among scolytid bark beetles, their associatedfungi, and live host conifers. Annu. Rev. Entomol. 42:179206.

Pettersson,E. M. 2001. Volatiles frompotential hosts ofRho-palicus tutela,a bark beetle parasitoid. J. Chem. Ecol. 27:22192231.

Pettersson, E. M., and W. Boland. 2003. Potential parasitoidattractants, volatilecomposition throughout a barkbeetleattack. Chemoecology 13: 2737.

Pettersson, E. M., E. Hallberg, and G. Birgersson. 2001. Ev-idence for the importance of odour-perception in theparasitoidRhopalicus tutela(Walker) (Hym., Pteromali-dae). J. Appl. Entomol. 125: 293301.

Raffa, K. F.,and D.L. Dahlsten. 1995. Differential responsesamong natural enemies and prey to bark beetle phero-mones. Oecologia (Berl.) 80: 556569.

Reeve, J. D. 1997. Predation and bark beetle dynamics. Oe-cologia (Berl.) 112: 4854.

Riley, M. A., and R. A. Goyer. 1986. Impact of benecialinsects onIpsspp. (Coleoptera: Scolytidae) bark beetlesin felled loblolly and slash pines in Louisiana. Environ.Entomol. 15: 12201224.

Safranyik, L., and A.L. Carroll. 2006. The biology and epi-demiology of the mountain pine beetle in lodgepole pineforests, pp.366. In L. Safranyik andB. Wilson (eds.), Themountain pine beetle: a synthesis of its biology, manage-ment and impacts on lodgepole pine. NRC, CFS, PFC,

Victoria, Canada.Salle, A., R. Monclus, A. Yart, J. Garcia, P. Romary, and F.

Lieutier. 2005. Fungal ora associated withIps typogra-phus: frequency, virulence, and ability to stimulate thehost defense reaction in relation to insect populationlevels. Can. J. For. Res. 35: 365373.


8/13/2019 Boone 2008

13/13

SAS Institute. 2003. SAS 9.1.3. SAS Institute, Cary, NC.Schroeder, L. M., and J. Weslien. 1994. Reduced offspring

production in bark beetle Tomicus piniperda in pine boltsbaited with ethanol and alpha-pinene, which attract an-tagonistic insects. J. Chem. Ecol. 20: 14291444.

Seybold, S. J., T. Ohtsuka, D. L. Wood, and I. Kubo. 1995.Enantiomeric composition of ipsdienol: a chemotaxo-nomic character for North American populations ofIpsspp. in the pini subgeneric group (Coleoptera: Scolyti-dae). J. Chem. Ecol. 21: 9951016.

Six, D. L. 2003. A comparison of mycangial and phoreticfungi of individual mountain pine beetles. Can. J. For.Res. 33: 13311334.

Six, D. L., and T. D. Paine. 1998. Effects of mycangial fungiand host tree species on progeny survival and emergenceof Dendroctonus ponderosae (Coleoptera: Scolytidae).Environ. Entomol. 27: 13931401.

Six, D. L., and T. D. Paine. 1999. Phylogenetic comparisonof ascomycete mycangial fungi and Dendroctonus barkbeetles (Coleoptera: Scolytidae). Ann. Entomol. Soc.Am. 92: 159166.

Solheim. H. 1992. The early stages of fungal invasion inNorway spruce infested by the bark beetleIps typogra-phus.Can. J. Bot. 70: 15.

Solheim, H., B. Langstrom, and C. Hellqvist. 1993. Patho-genicity of the bluestain fungiLeptographium wingfieldiiandOphiostoma minusto Scots pine: effect of tree prun-ing and inoculumdensity. Can. J. For. Res. 23: 14381443.

Sprechter, E., and H. P. Hanssen. 1983. Distribution andstrain-dependent formation of volatile metabolites in thegenus Ceratocystis. Antonie van Leeuwehoek 49: 493499.

Steidle, J.L.M., and J. A. van Loom. 2003. Dietary special-ization and infochemical use in carnivorous arthropods:testing a concept. Entomol. Exp. Appl. 108: 133148.

Sullivan, B. T., and C. W. Berisford. 2004. Semiochemicalsfrom fungal associates of bark beetles may mediate hostlocation behavior of parasitoids. J. Chem. Ecol. 30: 703717.

Sullivan, B. T., C. W. Berisford, and W. J. Dalusky. 1997.Field response of southern pine beetle parasitoids tosome natural attractants. J. Chem. Ecol. 23: 837856.

Sullivan, B. T., E. M. Pettersson, K. C. Seltmann, and C. W.Berisford. 2000. Attraction of the bark beetle parasitoidRoptrocerus xylophagorum (Hymenoptera: Pteromali-dae) to host-associatedolfactory cues. Environ. Entomol.29: 11381151.

Turlings, T. C., and B. Benrey. 1998. Effects of plant me-tabolites on the behavior and development of parasiticwasps. Ecoscience 5: 321333.

Upadhyay, H. P. 1981. A monograph of Ceratocystis andCeratocystiopsis. University of Georgia Press, Athens, GA.

Vasanthakumar, A., I. Delalibera, J. Handelsman, K. D.Klepzig, P. Schloss, and K. F. Raffa. 2006. Characteriza-tionof gut-associatedmicroorganisms in larvae andadultsof the southern pine beetle,Dendroctonus frontalisZim-

merman. Environ. Entomol. 35: 17101717.Vet, L.E.M. 1983. Host-habitat location through olfactorycues by Leptopilina clavipes (Hartig) (Hymenoptera: Eu-coilidae), a parasitoid of fungivorousDrosophila:the in-uence of conditioning. Neth. J. Zool. 33: 225248.

Weslien, J., and L. M. Schroeder. 1999. Population levels ofbark beetles and associated insects in managed and un-managed spruce stands. For. Ecol. Manag. 115: 267275.

Wood, D.L. 1982. Theroleof pheromones,kairomones,andallomones in the host selection behavior of bark beetles.Annu. Rev. Entomol. 27: 411446.

Received for publication 17 August 2007; accepted 18 Oc-tober 2007.


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