1010 Florida Entomologist 94(4) December 2011
COMPARATIVE ANALYSIS OF TERPENOID EMISSIONS FROM FLORIDA HOST TREES OF THE REDBAY AMBROSIA BEETLE, XYLEBORUS GLABRATUS (COLEOPTERA: CURCULIONIDAE: SCOLYTINAE)
JEROME NIOGRET, PAUL E. KENDRA*, NANCY D. EPSKY AND ROBERT R. HEATH United States Department of Agriculture, Agricultural Research Service, Subtropical Horticulture Research Station, 13601 Old Cutler Road, Miami, FL 33158-1857 USA
*Corresponding author; E-mail: [email protected]
ABSTRACT
The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Sco- lytinae), is an exotic wood-boring insect that vectors Raffaelea lauricola, the fungal patho- gen responsible for laurel wilt, a lethal disease of trees in the Lauraceae. First detected in the U.S. near Savannah, GA in 2002, X. glabratus has since spread throughout the south- eastern coastal plain causing high mortality in native Persea species, particularly redbay (P. borbonia) and swampbay (P. palustris). Currently, breeding populations of X. glabratus pose an imminent threat to the avocado (P. americana) industry in south Florida. There is a crit- ical need for effective attractants to detect, monitor, and control the spread of this invasive pest. In an effort to identify host-based attractants for dispersing female X. glabratus, we conducted a comparative study of the volatile chemicals emitted from wood of six species of Lauraceae found in Florida: avocado (Persea americana), redbay (P. borbonia), swampbay (P. palustris), silkbay (P. humilis), camphor tree (Cinnamomum camphora), and lancewood (Ocotea coriacea). We compared chemical profiles to those obtained from wood of lychee, Lit- chi chinensis (Sapindaceae), a presumed non-host found to be highly attractive to X. glabra- tus in field tests. GC-MS analysis identified 11 terpenoid compounds common to all lauraceous species. Of these, 4 sesquiterpenes were also found in lychee: a-copaene, b-caryo- phyllene, a-humulene and cadinene. Future research will include field tests and laboratory bioassays to evaluate the roles of each of these potential kairomones.
Key Words: Lauraceae, avocado, sesquiterpenes, kairomones, a-copaene, b-caryophyllene, a- humulene and cadinene
RESUMEN
El escarabajo ambrosia de laurel rojo, Xyleborus glabratus Eichhoff (Coleoptera: Curculioni- dae: Scolytinae), es un insecto barrenador exótico que es un vector de Raffaelea lauricola, el hongo patógeno responsable de la marchitez del laurel, una enfermedad mortal de los árbo- les de la familia Lauraceae. Detectado por primera vez en los EE.UU. cerca de Savannah, Georgia en el año 2002, X. glabratus se ha extendido su rango desde entonces a la llanura costera del sureste causando mortalidad alta en las especies nativas de Persea, en particular del laurel rojo (P. borbonia) y swampbay (P. palustris). En la actualidad, las poblaciones re- productoras de X. glabratus representan una amenaza inminente para la industria del aguacate (P. americana) en el sur de la Florida. Hay una necesidad critica de atrayentes efi- caces para detectar, monitorear y controlar la propagación de esta plaga invasora. En un es- fuerzo por identificar atrayentes con base a los hospederos para la dispersión de hembras de X. glabratus, se realizó un estudio comparativo de los productos químicos volátiles emitidos a partir de madera de seis especies de Lauraceae en Florida: aguacate (Persea americana), del laurel rojo (P. borbonia), swampbay (P. palustris), silkbay (P. humilis), árbol de alcanfor (Cinnamomum camphora), y lancewood (Ocotea coriacea). Se compararon los perfiles quími- cos con los perfiles obtenidos de madera de lichi, Litchi chinensis (Sapindaceae), que supues- tamente no es un hospedero de X. glabratus pero fue muy atractiva para S. glabratus en pruebas de campo. El análisis de CG-EM (Cromatografia de Gases y Espectrometria de Ma- sas) identificó nueve compuestos terpenoides común a todas las especies de Lauraceae. De ellos, tres sesquiterpenos se encontraron también en lichi: a-copaeno, b-cariofileno, a-humu- leno y cadineno. Las investigaciones futuras se incluiran pruebas
Ambrosia beetles (Curculionidae: Scolytinae xylem of host trees (Rabaglia 2002). Typically in- and Platypodinae) comprise a diverse group of festing weak or dying trees, most species are not morphologically-similar wood borers that culti- of economic importance and have not been stud- vate and feed on symbiotic fungi growing on the ied well. The redbay ambrosia beetle, Xyleborus
Niogret et al.: Terpenoids Emitted by Host Trees of Xyleborus glabratus in Florida 1011
glabratus Eichhoff, is not a pest in its native dis- (14.4 km) north of commercial avocado groves. tribution in southeastern Asia. It acquired pest Avocado production represents an estimated $14 status upon entry into the U.S., where it vectors million annually at the farm gate for the state of the fungal pathogen, Raffaelea lauricola T.C. Florida (USDA-NASS 2011). In addition, replace- Harr., Fraedrich & Aghayeva (Harrington et al. ment costs of commercial and residential avocado 2008), that causes laurel wilt, a newly described trees in Miami-Dade, Broward, Palm Beach and lethal disease of trees in the family Lauraceae Lee Counties have been estimated at $429 million (Fraedrich et al. 2008). First detected in 2002 (Evans & Crane 2008). near Savannah, Georgia (Rabaglia et al. 2006), X. Due to the serious ecological and economic im- glabratus has since spread into the Carolinas, pact of laurel wilt disease, there is a critical need Florida and Mississippi (USDA-FS 2011). Xyle- for effective attractants to detect, monitor, and borus glabratus functions as a primary colonizer control the spread of the vector. To date, no aggre- of U.S. hosts, capable of attacking apparently gation pheromone has been identified for X. gla- healthy trees (Hanula et al. 2008). During gallery bratus. Initial research by Hanula et al. (2008) in- excavation, females introduce spores of several dicated no significant attraction of X. glabratus to symbiotic fungal species (Harrington et al. 2010). its fungal symbiont, to its frass, or to ethanol (the While providing food for the adults and larvae, standard attractant for ambrosia beetles). Host the symbiotic fungus also invades the host vascu- tree volatiles (secondary metabolites) appear to lar system. Infected trees respond to R. lauricola be the primary attractants used by dispersing fe- by secreting resins and forming walls (parenchy- males. Additional studies conducted in South mal tyloses) within the xylem vessels. This defen- Carolina (Hanula & Sullivan 2008) identified 2 sive response results in blockage of water trans- essential oils as attractive baits for monitoring X. port, systemic wilt, and ultimately tree death, glabratus, i.e., manuka oil and phoebe oil [essen- which has been observed to occur in as little as 6 tial oil extracts from the tea tree, Leptospermum weeks under experimental conditions (Mayfield scoparium Forst. & Forst. (Myrtaceae) and the et al. 2008). Brazilian walnut, Phoebe porosa Mex. (Lau- Native Persea species in north and central raceae), respectively]. Based on that report, the Florida have suffered high mortality due to laurel current monitoring system for X. glabratus con- wilt, particularly redbay [P. borbonia (L.) sists of Lindgren multi-funnel traps baited with Spreng.] and swampbay [P. palustris (Raf.) Sarg.], manuka oil lures (CISEH 2010). However, recent which appear to be preferred hosts in the U.S. field tests conducted in Florida indicated that Fraedrich et al. (2008) reported that redbay mor- manuka lures were not competitive with host av- tality increased from 10% to more than 90% in 15 ocado wood, had limited longevity (Kendra et al. mo at the site where X. glabratus was first de- 2011a), and captured numerous non-target am- tected in Florida. Redbay plays an important role brosia beetles (Kendra et al. 2011b). Phoebe lures in the natural ecosystem, furnishing food (fruit, were found to be highly effective for capture of X. seed and foliage) for songbirds, wild turkey, quail, glabratus (Kendra et al. 2011a), but unfortu- deer, and black bear (Brendemuehl 1990; nately, they are no longer available due to deple- Fraedrich et al. 2007), and Persea species are the tion of source trees in the Brazilian rain forest. primary larval hosts of the palamedes swallow- Based on a comparison of volatile emissions from tail, Papilio palamedes Drury, Lepidoptera: Papil- manuka oil, phoebe oil, and chipped redbay wood, ionidae (Scott 1986). Other Lauraceae susceptible Hanula & Sullivan (2008) hypothesized that two to laurel wilt disease include silkbay (Persea hu- sesquiterpenes, a-copaene and calamenene, were milis Nash), sassafras [Sassafras albidum (Nut- host-based attractants (kairomones) for X. gla- tall) Nees], camphor tree [Cinnamomum cam- bratus.
phora (L.) J. Presl.], spicebush [Lindera benzoin Terpenoids (C10 monoterpenes and C15 sesquit- (L.) Blume], pondberry [Lindera melissifolia erpenes) are secondary plant metabolites known (Walter) Blume], and pondspice [Litsea aestivalis to play various roles in insect-host interactions. (L.) Fernald] of which the latter two are listed as They are located within the cambium layers (de- endangered species at the state and/or federal fined as the lateral meristem including the vascu- level (Fraedrich et al. 2008; HSPD-9 2009). The lar cambium and cork cambium in vascular widespread availability of host trees in Florida, in plants), and typically consist of several major combination with human transport of infested compounds accompanied by derivatives and mi- material (primarily firewood, FDACS-DPI 2010), nor components. Some terpenoids function as de- have contributed to a rapid southward spread of fensive compounds, being either toxic or repellent the vector-disease complex, which currently to deter attacks by phytophagous insects (Gersh- threatens another Persea species, avocado (P. enzon & Croteau 1991; Byers et al. 2000; Byers et americana Mill). In February 2011, laurel wilt al. 2004). Terpenoids emitted from herbivore- and breeding populations of X. glabratus were de- damaged plants have been shown to attract natu- tected in stands of swampbay trees in Miami- ral enemies and confer indirect plant protection Dade County (FDACS 2011), less than 9 miles (Pettersson et al. 2000). Terpenoids also function
1012 Florida Entomologist 94(4) December 2011 prominently in host location by herbivorous in- (Analytical Research Systems, Inc., Gainesville, sects (Miller & Strickler 1984; Visser 1986). Pre- Florida) connected to the bag for 60 and 30 min, vious studies showed that bark beetles utilize ter- respectively. Chemicals were eluted from the su- pene olfactory cues for host recognition, finding per-Q adsorbent using 200 µL of high purity me- appropriate host trees either by attraction to, or thylene chloride (99.5% pure; ACROS, Morris repulsion from, plant volatiles from a distance Plains, New Jersey). Chemical profiles from in- (Byers 1995). tact and damaged branches were qualitatively This report presents results from a compara- compared with the chemical profiles from the tive study of volatile chemicals emitted from rasped cambial samples (1g) prepared using the known host trees of X. glabratus. Using gas chro- protocol described below. matography-mass spectroscopy (GC-MS) of vola- tiles collected from wood substrates, we identified Host Material and compared the principal terpenoids emitted from avocado and five species of Lauraceae that Seven tree species were evaluated in this occur sympatrically in south Florida, i.e., redbay, study, consisting of avocado (cv ‘Brooks Late’, P. swampbay, silkbay, camphor tree, and lancewood americana var. guatemalensis Williams) and ly- [Ocotea coriacea (Sw.) Britton]. Lancewood has chee (cv ‘Hanging Green’) obtained from the ger- not been confirmed a host for X. glabratus, but mplasm collection at the USDA-ARS Subtropical was included in this study as a potential host Horticulture Research Station (Miami, Florida); since it is a laurel tree native to south Florida, silkbay collected from the Lake Wales Ridge at commonly found in coastal hammocks and pine- Archbold Biological Station (Lake Placid, Flor- lands. We compare the chemical profiles from the ida); redbay collected at Snyder Park (Ft. Lauder- Lauraceae to that obtained from wood of lychee dale, Florida); swampbay collected at Deering Es- (Litchi chinensis Sonn.; Sapindaceae), a pre- tate (Miami, Florida); camphor tree collected at sumed non-host recently found to be high in a-co- Montgomery Botanical Center (Miami, Florida), paene (Niogret et al. 2011) and highly attractive Bok Tower Gardens (Lake Wales, Florida), and a to X. glabratus in field tests (Kendra et al. 2011a). private residence (Lake Placid, Florida); and We also evaluate results of the chemical analyses lancewood collected at Matheson Hammock (Mi- in terms of attraction and behavioral responses of ami, Florida). X. glabratus documented in previous laboratory and field studies. With this comprehensive ap- Chemical Collection and Analysis proach, we hope to gain a better understanding of the chemical ecology of this new invasive species, Samples for chemical analysis of host trees and more specifically to identify chemical attrac- were prepared by manually rasping the outer lay- tants with potential for improved pest detection ers (bark and cambial tissue) from freshly-cut and control. branches (4.4 ± 0.6 cm diam., 3-9 replicate trees per species) using a microplaner. Samples were MATERIALS AND METHODS collected and analyzed within 24 h after branch removal, and within 5 min after rasping the cam- Evaluation of Sampling Method bium. Volatiles were collected from rasped wood samples (6 g per replicate) using traps filled with Preliminary chemical analyses were per- super-Q as the adsorbent (Analytical Research formed to determine if sample preparation by Systems) according to methods published previ- manual rasping of avocado tree branches (Niogret ously (Heath & Manukian 1992; Heath et al. et al. 2011) resulted in the induction of volatile 1993). Wood samples were spread in a cylindrical chemicals not present in undamaged branches. glass chamber (4.5 cm diam., 25 cm length), puri- Samples were collected outdoors from the fied air was introduced into the chamber (1 L min- branches of 3 field-grown avocado trees (8 cm 1), and headspace volatiles were collected for 15 branch diam., 3 replicate samples per tree). Vola- min. Collector traps were cleaned by soxhlet ex- tile collections were performed using an outdoor traction using methylene chloride for 24 h and super-Q collection system consisting of an oven dried in a fume hood prior to use. Volatile chemi- bag (Reynolds, Richmond, Virginia) tightly cals were eluted from the super-Q adsorbent us- wrapped around: 1) a 30 cm length of intact ing 200 µL of high purity methylene chloride branch, and 2) a 30 cm length of the same branch (99.5% pure; ACROS). For quantitative analysis, immediately after manual rasping of bark and an aliquot of C16 standard (5 µg) was added to each cambium (5 cm2 area). The bag was connected to sample prior to injection onto the GC column. push-pull pumps (Cole-Parmer, Vernon Hills, Illi- Chemical extracts were analyzed using a gas- nois) producing a 1 L min-1 air flow, powered by a chromatograph (ThermoQuest Trace GC 2000, 12 volt car battery. Volatile chemicals were col- Austin Texas). The column was fused silica, 25 m lected from the intact and damaged branches us- long, 0.25 mm I.D, DB-5MS phase (J&W Scien- ing traps containing super-Q as the adsorbent tific, Agilent Technologies, Santa Clara, Califor-
Niogret et al.: Terpenoids Emitted by Host Trees of Xyleborus glabratus in Florida 1013 nia), programmed from 50-130 °C at 15.0 °C min- secondary metabolites. Research with the emer- 1, then from 130-220 °C at 10.0 °C min-1 and held ald ash borer, Agrilus planipennis Fairmaire (Co- at 220 °C for 4 min. The following parameters leoptera: Buprestidae), showed increased attrac- were used for the Mass Spectrometer (Agilent tion of beetles to stressed (girdled) host trees Technologies 5975B): EI energy: 69.9eV, MS (Crook et al. 2008). That attraction was correlated source and MS quadrupole at 230 and 150 °C re- with increased production of several sesquiterpe- spectively, Electron Multiplier 1294V. The column nes, however elevated levels of those induced used in the gas chromatograph interface to the compounds were not observed until 24 h after tree mass spectrometer was 25 m long, 0.25 mm I.D injury. DB-5MS phase (J&W Scientific, Agilent Technol- ogies) programmed at 40 °C for 2 min, then from Chemical Analysis 40-130 °C at 10.0 °C min-1, then from 130-220 °C at 20.0 °C min-1 and then held at 220 °C for 4 min. A total of 55 volatile chemicals (detected at Chemicals were identified using the NIST Mass quantities ≥ 0.5 µg in at least one of the replicate spectral program version 2.0d and NIST/EPA/ samples) were isolated and identified by super-Q NIH mass spectral library (NIST05) when Re- collections and GC-MS analysis. Of those com- verse Matches and Matches were >950 and pounds, there were 11 terpenoids (4 monoterpe- >900‰, respectively. nes and 7 sesquiterpenes) common to the laura- For each terpenoid (Table 1), the Kovats Re- ceous hosts, which can be regarded as constitut- tention Index (RI) was calculated based on sepa- ing a generalized bouquet or ‘volatile signature’ of ration on the DB-5MS column. To verify chemical the Lauraceae (Table 1). Among the species eval- identifications generated by the mass spectral li- uated, the terpenoid profile varied both qualita- brary, the RI values of sample peaks were com- tively and quantitatively. Two of those com- pared with the RI values obtained from synthetic pounds (RI 1047 and 1425) have yet to be identi- chemicals (when commercially available) or with fied due to inconsistent matches in the NIST previously published data obtained with compa- mass spectral library. rable GC methods. Synthetic chemicals consisted Monoterpenes, particularly a- and b-pinene, of a-pinene (Aldrich Chemical Co., Milwaukee, were the dominant volatiles detected from the na- Wisconsin), b-pinene (Aldrich Chemical Co.), li- tive Persea species. b-pinene made up 51, 45, and monene (Glidden Organics of SCM Corp., Jack- 21% of the terpenoid emissions from silkbay, red- sonville, Florida), a-cubebene (Bedoukian Re- bay, and swampbay samples, respectively; and a- search, Inc., Danbury Connecticut), a-copaene pinene was the dominant compound (41%) in (Fluka Analytical, Stenheim, Germany), b-caryo- swampbay. Camphor tree also had high monoter- phyllene (Sigma Chemical Co., St. Louis, Mis- pene emissions, consisting of 12, 12, and 10% of a- souri), a-humulene (Sigma Chemical Co.) and thujene, b-pinene and an unknown monoterpene cadinene (Fluka Chemie, Buchs, Switzerland). (RI 1047), respectively. The lancewood profile was We were not able to confirm the identification of composed almost entirely of pinene volatiles (58 chemicals emitted in very low quantity (<1µg) but and 37% b- and a-pinene, respectively). Pinenes we compared their RI with RI from published re- have been documented as attractants for related ports (a-thujene (Singh et al. 2007) and calame- species of ambrosia beetles, including Xyleborus nene (Ibrahim et al. 2010)). Calamenene and pubescens Zimmermann (Miller & Rabaglia 2009) cadinene were previously reported in the litera- and Xyleborinus saxesenii (Ratzeburg) (Petrice et ture in redbay (Hanula & Sullivan 2008) and b- al. 2004). However, pinene emissions from avo- caryophyllene was previously reported in seeds and cado, a confirmed host (Mayfield et al. 2008), were leaves of camphor trees (Yong & Wenyi 2002; Zhu much lower than from the 3 native Persea spp., & Guo 2010). and only trace amounts of pinenes (and monoter- penes in general) were detectable from lychee RESULTS AND DISCUSSION wood, a substrate highly attractive to X. glabra- tus and other Scolytinae in Florida (Kendra et al. Evaluation of Sampling Method 2011a,b). These data suggest that, although pinenes are released at high levels from the pre- No qualitative differences in chemical profiles ferred hosts (native Persea spp.), they are not pri- were detected among the 3 avocado samples (in- mary host attractants for female X. glabratus. tact branch, newly-damaged branch, and newly- Hanula et al. (2008) came to the same conclusion, rasped cambial sample), leading to the conclusion finding no attraction of X. glabratus to freshly-cut that production of chemicals was not induced at bolts of loblolly pine (Pinus taeda L.), a species detectable levels during the time period evalu- high in both a- and b-pinene. It is plausible, how- ated (30 min). Newly-rasped samples contained ever, that pinenes may function as synergistic at- the same chemical components as the intact tractants when they co-occur with appropriate branches, only at much higher levels, which re- laurel sesquiterpenes, such as a-copaene. Syner- sulted in improved sensitivity in detection of host gism among volatile attractants has been well 1014 Florida Entomologist 94(4) December 2011 c c c c c c d HUMI-
LYCHEE
e c AND 0.3 ± 0.4 ± 0.0 3.6 ± 0.5 2.3 ± 0.5 0.1 ± ERSEA 23.6 ± 3.5 15.8 ± 4.7 <0.05 <0.05 P ), ( c c c c c e c d SILKBAY CORIACEA
e ), 0.2 ± 1.6 ± 0.7 0.2 ± 0.10 0.1 ± 0.3 ± 0.1 ± 0.0 COTEA <0.05 19.5 ± 17.4 30.3 ± 19.5 O ( AMERICANA
c b d c c c e c e ERSEA ). P LANCEWOOD ( 9.0 ± 3.2 3.4 ± 1.9 8.6 ± 4.4 9.6 ± 4.2 10.4 ± 6.7 0.6 ± 0.2 2.4 ± 0.7 1.1 ± 0.4 ), 23.0 ± 12.3 COLUMN
c AVOCADO c c MS d c e bd bd
bd -5 CAMPHORA
DB FROM (
0.3 ± 0.2 0.9 ± 0.2 0.2 ± 0.1 0.6 ± 0.2 1.4 ± 1.6 11.9 ± 9.2 49.0 ± 17.4 1.9 ± 0.7 10.3 ± 3.4 NALYSIS SAMPLES
INNAMOMUM c c d c c e d d C ( WOOD e
TREE GC-MS A
0.6 ± 0.4 5.1 ± 8.9 ± 2.9 0.9 ± 1.3 0.9 ± 1.0 4.5 ± 4.6 44.5 ± 26.8 22.0 ± 12.4 <0.05 AND
RASPED
G c c c 6 CAMPHOR c d c c c d ), FROM
COLLECTION 0.3 ± 0.2 7.5 ± 4.4 2.1 ± 1.0 1.5 ± 0.2 4.8 ± 3.9 -Q 24.0 ± 27.7 12.3 ± 3.6 25.4 ± 11.2 100.3 ± 60.3 BORBONIA
EMITTED
SUPER
c c c d c c c c d ERSEA BY
P ( Avocado Silkbay Swampbay Redbay Camphor Lancewood Lychee TERPENOIDS 11.4 ± 1.8
REDBAY ISOLATED
), WERE
c VOLATILE
a OF ) PALUSTRIS
SD ± VOLATILES ). ERSEA P ( MEAN (µG, CHINENSIS
SWAMPBAY ), ITCHI UANTITY L ( LIS 1. Q Identification by NIST library. Mean Kovats Retention Index calculated from 3-9 replicates per species. Previously reported in published reports (see text). Identification verified by comparison with RI from published reports (see text). Identification verified by comparison with synthetic chemicals (see text). a b c d e ABLE 1 a-thujene 932 0.6 ± 0.1 2345 a-pinene6 b-pinene7 Unknown 18 a-cubebene9 a-copaene Unknown 2 944 b-caryophyllene 1047 992 a-humulene 1360 1442 1394 1425 7.8 ± 1.3 3.9 ± 1.2 6.6 ± 1.1 1477 14.4 ± 7.6 12.9 ± 5.0 18.9 ± 19.3 0.3 ± 0.1 1.3 ± 0.7 17.9 ± 19.9 6.3 ± 4.2 28.1 ± 43.4 7.7 ± 6.8 7.6 ± 7.9 7.0 ± 2.1 <0.05 0.4 ± 0.2 <0.05 0.1 ± 0.0 0.3 ± 1011 Cadinene Calamenene 1538 1532 1.3 ± 1.2 1.6 ± 0.7 Peak Chemical RI T Niogret et al.: Terpenoids Emitted by Host Trees of Xyleborus glabratus in Florida 1015 documented in other insect systems (Heath et al. elevated levels from stressed ash trees), all elicit 2004; Kendra et al. 2008). consistent olfactory responses in electroantenno- Among the sesquiterpenes detected, there graphic analyses with A. planipennis (Crook et al. were 7 chemicals found in common to the 6 spe- 2008); and a- and b-cadinene are known attracta- cies of Lauraceae (Fig. 1, peaks 5-11). Of those 7, nts for the European elm bark beetle, Scolytus 4 were also present as significant components in multistriatus (Marsham), a vector of Dutch elm the lychee sample (Fig. 1G): a-copaene (peak 6), b- disease (Millar et al. 1986). caryophyllene (peak 8), a-humulene (synonymous The results of this comparative host study are with b-caryophyllene; peak 9; this chemical was consistent with results from previous field tests identified in avocado and silkbay but not clearly (Kendra et al. 2011a) that evaluated attraction of confirmed in other samples due to the low amount X. glabratus to manuka lures, phoebe lures, ly- emitted, despite a similar RI) and cadinene (peak chee wood (cultivar unknown), and avocado wood 10; analysis could not discern enantiomeric con- (3 cultivars representative of West Indian, Guate- figuration). As ‘common denominators’ among the malan, and Mexican races). In that study, field attractive wood substrates, these 4 sesquiterpe- captures of X. glabratus were positively corre- nes are the most likely candidates that should be lated with substrate levels of a-copaene, b-caryo- evaluated as kairomones for X. glabratus. Each of phyllene and a-humulene. Lychee wood had the these sesquiterpenes has been implicated previ- highest a-copaene content and also caught signif- ously as a host-based semiochemical for other icantly more X. glabratus than any of the other species of wood-boring beetle. For example, a-co- treatments. Lychee wood was also more attrac- paene, b-caryophylleneand a-humulene (emitted at tive than avocado wood in two-choice laboratory bioassays (Kendra et al. 2011a). In the current study, a-copaene made up 55% of the total emis- sions from lychee (cv ‘Hanging Green’), and was a prominent sesquiterpene in all of the lauraceous hosts, especially the Persea species. These results support the conclusion of Hanula and Sullivan (2008) that a-copaene functions as a primary host attractant for X. glabratus. Hanula and Sullivan (2008) also identified ca- lamenene as another potential kairomone based on a comparison of volatiles from redbay wood, manuka oil, and phoebe oil (both essential oils in neat form). However, our GC analyses detected ca- lamenene (Fig. 1, peak 11), as a major peak only in wood from silkbay and swampbay but this chemi- cal was not clearly identified in camphor. Moreover captures of X. glabratus were not correlated with calamenene in previous field tests with avocado and lychee wood (Kendra et al. 2011a). In addition, quantification of calamenene was low from com- mercial phoebe lures after just 1 week in the field (the dominant volatile emitted was a-copaene, 38%), despite high captures of X. glabratus over the 8-wk test (Kendra et al. 2011a). Therefore, ca- lamenene did not appear to play a significant role in attraction to avocado, lychee, or phoebe oil lures, but it may potentially be a synergistic attractant in the native Persea species. Neither calamenene nor a-copaene has been evaluated directly as a field lure, due to lack of commercial availability in quantities sufficient for field tests. As a side note, there is current disagreement among plant taxonomists regarding species and Fig. 1. Representative GC analyses (DB-5MS col- varietal differences among the Persea representa- umn) of sesquiterpenes obtained by super-Q collections tives in the southeastern U.S. (Brown & Kirkman from wood of (A) avocado (Persea americana), (B) silk- 1990; Coder 2006). The chemical analyses pre- bay (Persea humilis), (C) redbay (Persea borbonia), (D) swampbay (Persea palustris), (E) camphor tree (Cinna- sented herein identified both qualitative and momum camphora), (F) lancewood (Ocotea coriacea), quantitative differences among monoterpenes and (G) lychee (Litchi chinensis). Peak numbers corre- and sesquiterpenes from freshly-rasped wood of spond to chemical identifications presented in Table 1. redbay, swampbay, and silkbay trees. These 1016 Florida Entomologist 94(4) December 2011
chemotaxonomic data, in combination with tradi- BYERS, J. A., ZHANG, Q. H., AND BIRGERSSON, G. 2004. tional morphological characters, may facilitate a Avoidance of non-host plants by a bark beetle, Pityo- better understanding of the phylogenetic rela- genes bidentatus, in a forest of odors. Naturwissen- tionships within the genus Persea. schaften 91: 215-219. CISEH. 2010. Forestry images. Lindgren funnel trap. Center for Invasive Species and Ecosystem Health, CONCLUSIONS USDA Forest Service, and International Society of A comprehensive comparison of volatile chem- Arboriculture.
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