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Chemical Ecology of Xyleborus glabratus and Implications for Monitoring and Management
Paul E. Kendra, Wayne S. Montgomery, Jerome Niogret,Elena Q. Schnell, and Nancy D. Epsky
USDA‐ARS, Subtropical Horticulture Research Station
13601 Old Cutler Road, Miami, FLemail: [email protected]
-----------------------------------------------------------------------------------------------------------------------Conference on Laurel Wilt Disease and Natural Ecosystems: Impacts, Mitigation, and the Future
16-18 June 2015
Applied Approach• Target = Adult female RAB, host‐seeking flight• Dispersal flight is risky
– Harsh environment (dessication, wind, rain)– Predation (e.g. dragonflies)– No food available
• Strong selection– Reliable cues to find host trees quickly– Optimize timing of flight to minimize risks
Chemical Ecology of RAB
– Initial research on RAB attractants(Hanula et al. 2008, Hanula & Sullivan 2008)
• No evidence of pheromones (aggregation or sex)• No long‐range attraction to fungal symbionts• No attraction to ethanol (standard lure for ambrosia beetles)
– Conclusions:• RAB can attack healthy, unstressed trees• Host tree volatiles = primary attractants• α‐copaene, calamenene are likely attractants from redbay; but cost/availability make them impractical for field lures
• Manuka and phoebe oils identified as attractive baits for RAB
ARS ‐Miami,FLResearch ‐ RAB attractants (2009‐pres.)Multidisciplinary approach
• Field tests (forest sites)
• Lab tests (Archbold Biol. Station, Lake Placid)– Behavioral bioassays (attraction, boring preferences)– Electrophysiology techniques to measure olfactory responses
• Chemical sampling & analysis (Miami)– Volatile collections– Gas chromatography‐
mass spectrometry(GC‐MS)
1. Method for Capture of Live RAB
General Method• Late afternoon (~4:00 pm)• Lay cotton sheet on ground• Bait = Freshly‐cut host wood• “Lure in” ambrosia beetles• Collect with soft brush
Kendra et al. 2012 FL Entomol.
Unique Observation: Temporal Separation of Beetle Species
• Multiple species attracted to wood volatiles
• X. glabratus flies earlier(27 collection dates, Apr‐Oct 2011)
• Useful method for obtaining RAB in host‐seeking behavior, the perfect stage to evaluate attractants‐ Lab bioassays‐ Electrophysiology studies
1600 1630 1700 1730 1800 1830 1900 1930 2000
Num
ber
of F
emal
es C
olle
cted
0
2
4
6
8
10
12
14
Time Interval
1600 1630 1700 1730 1800 1830 1900 1930 2000
Num
ber
of F
emal
es C
olle
cted
0
1
2
3
4
5
6
X. ferrugineus
X. glabratus
1600 1630 1700 1730 1800 1830 1900 1930 2000
Num
ber
of F
emal
es C
olle
cted
0
10
20
30
40
50
60
70
X. affinis
Kendra et al. 2012 Environ. Entomol.
sunset
2. Electroantennography (EAG)Technique to measure olfactory response of antennal receptors(How well does an insect smell a particular chemical?)
• Mount antenna between 2 electrodes• Place under purified air flow• Deliver chemical sample• Measure receptor potential
EAG lab at Archbold Biol. StationA B C
Sample EAG recordings from single RAB antenna
EAG TechniqueMajor challenge: small size of RAB antenna (0.3‐0.4 mm length)• Used a gold, 2‐pronged electrode• Electrode modified by attaching a flexible gold wire to one prong
Scanning electron micrograph of RAB antenna
Modified antennal electrode
Validation of New EAG MethodsComparative studies with 3 species:X. glabratus, X. affinis, and X. ferrugineus
• Ethanol = standard reference chemical• EAG responses to test chemicals could then beexpressed as a percentage relative to ethanol X. glab X. affin X. ferr
EAG
Res
pons
e (-
mV)
0.0
0.5
1.0
1.5
2.0
2.5
aa
aEthanol
Silkbay wood
X. glab X. affin X. ferr
EA
G R
espo
nse
(%)
0
20
40
60
80
100
Phoebe oil
X. glab X. affin X. ferr0
20
40
60
80
100
Manuka oil
X. glab X. affin X. ferr0
20
40
60
80
100
A. B. C.a
b b
a
b b
a
bab
Kendra et al. 2012. Environ. Entomol.
3. Bolt Boring Bioassay• No‐choice tests to assess RAB boring behaviors
– 1‐gallon bucket– 1 bolt plus 10‐15 female RAB – Recorded # RAB boring and location on bolt after 2, 4, 6,8, 24 hr(Positive boring = half ofthe body inserted)
– Replicated 5x
Kendra et al. 2013 FL Entomol.
Composite Results – Bioassays
Time (hr)
0 5 10 15 20 25
Perc
enta
ge o
f Fe
mal
es B
orin
g
0
20
40
60
80
100 Silkbay (99%)
Swampbay/Redbay (91%)
Avocado (80%)
Camphor tree (50%)
Lancewood (44%)
Live Oak (0%)
(Adapted from Kendra et al. 2014 PLoS ONE)
>70% boring on cut end; trees most susceptible to attack after pruning or injury.
4. Comparative Field Tests• Replicated field tests with freshly‐cut wood bolts• Silkbay most attractive = positive control; captures normalized• Determined relative attraction of 9 species within Lauraceae
Silkba
yCam
phor.
Cal. Bay
Sassa
fras
Swampa
yRed
bay
Avoca
doLa
ncew
ood
Spiceb
ush
Live O
akCon
trol
Nor
mal
ized
Cap
ture
s
0.0
0.2
0.4
0.6
0.8
1.0a a
bb b b
c c c
b
bc
Kendra et al. 2014 PLoS ONE
5. Chemical Analysis
• Emissions of terpenoids from bolts correlated with RAB captures in field
• 4 sesquiterpenes– Major
• α‐cubebene (peak 2)
• α‐copaene (peak 3)
– Minor• α‐humulene (peak 6)
• calamenene (peak 8)Kendra et al. 2014 PLoS ONE
Current Hypothesis ‐ Host Location, AcceptanceLong‐range: RAB in flight attracted to the odor plume from host trees.
Terpenoids: α‐copaene, α‐cubebene, α‐humulene, calamenene(Hanula & Sullivan 2008, Kendra et al. 2011, 2014); eucalyptol (Kuhns et al. 2014); other monoterpenes (Martini et al. 2015)
Mid‐range: RAB uses visual cues to find hosts of appropriate diameter (Mayfield and Brownie 2013)
Short‐range: RAB detects (1) terpenoid gradients to find best site for attack (avocado: α‐copaene and α‐cubebene) (Niogret et al. 2013), and (2) fungal odors = food attractants (Hulcr et al. 2011, Kuhns et al. 2014)
On contact: RAB ‘taste’ and ‘feel’ the wood to confirm suitability(eucalyptol, Kuhns et al. 2014)
Summary: Host must smell, look, taste,and feel ‘right’ before boring initiated.
Development of Field Lures for RAB
• First lures = phoebe oil, manuka oil (Hanula & Sullivan 2008)• However, tests in FL (2009‐2010) indicated that manukalures not very effective
Phoeb Guat W.Ind Mex Manuk Contr
Beet
les
/ tra
p / w
eek
0.0
0.5
1.0
1.5
2.0
X. glabratus(mean ± SE)
8-wk testAlachua Co., FL
a
aab
b
c c
(Kendra et al. 2011. J. Chem. Ecol.)
Follow‐up Tests Confirmed Results
• Phoebe caught 6X more RAB• Manuka lost attraction after 3 wk• Unfortunately, phoebe lures no longer available, manuka lures
only option for RAB monitoring
Phoebe Manuka Control
Beet
les
/ tra
p / w
k
0
5
10
15
20
25
a
b
c
Xyleborus glabratus(mean + SE)
12-wk testHighlands Co., FL
(Kendra et al. 2012. J. Econ Entomol.)
Xyleborus glabratusWeekly Captures over Time
Week
0 2 4 6 8 10 12 14
Beet
les
/ wee
k
0
50
100
150
200
250
300
350
PhoebeManukaControl
Freeze
Evaluation of Other Essential Oils
Field tests in 2012 compared 7 essential oils for RAB attraction:(Homemade lures – 2 ml oil)
• Manuka• Phoebe• Cubeb• Ginger root• Angelica seed• Tea tree• Valencia orange
(Agricultural Research 2012)
Cubeb oil identified as a new RAB attractant(from berries of tailed pepper Piper cubeba)
X. glabratus (mean + SE)4-wk test (25 Apr - 23 May 2012)
Essential oil
Man Cub Phb Gin Ang Tea Ora Blk
Bee
tles
/ tra
p / w
eek
0
2
4
6
8
10
12
aa
a
bb
bcc c
(Kendra et al. 2013. Am. J. Plant Science)
Field Tests 2013Collaboration with Synergy Semiochemicals Corp. (BC, Canada)
New lure = distilled cubeb oil in bubble lure(enriched in sesquiterpenes)
Field tests to compare efficacy andlongevity of commercial lures:
• Cubeb bubble lure• Manuka lure• Phoebe lure• Unbaited control
Test 1 (Highlands County, FL)
• Cubeb bubble lure captured 3 times more RAB than manuka
Xyleborus glabratus (mean + SE)
8-wk Field Test (5 reps)Archbold Biol. Station (Lake Placid, FL)
(28 Feb - 25 Apr 2013)
cubeb manuka blank
RAB
/ tra
p / w
k
0
1
2
3
4
5
6
7
a
b
c
Xyleborus glabratus - Weekly captures
Week
0 1 2 3 4 5 6 7 8 9 10
RA
B /
wk
0
10
20
30
40
50
60
CubebManukaControl
(Kendra et al. 2014. J. Pest Science)
Test 2 (Glades County, FL)
• At very low population levels, cubeb bubble lure captured 6 times more RAB than manuka
Xyleborus glabratus (mean + SE)
8-wk Field TestFisheating Creek State Park
(8 Mar - 3 May 2013)
Cubeb bubble Manuka patch Control
Beet
les
/ tra
p / w
eek
0.0
0.5
1.0
1.5
2.0
2.5
a
b
b
(Kendra et al. 2014. J. Pest Science)
Test 3 (Highlands County, FL)
• Cubeb > phoebe > manuka• Cubeb field life of 3 months
(Kendra et al. 2015. J. Econ. Entomol.)
Cubeb Phoebe Manuka Control
Beet
les
/ tra
p / w
k
0
2
4
6
8
10
12
14
16
18 a
b
c
c
Xyleborus glabratus (mean + SE)
12-wk Field Test Highlands Hammock State Park
Week
1 2 3 4 5 6 7 8 9 10 11 12
Beet
les
/ wee
k
0
20
40
60
80
100
120
140
160Cubeb Phoebe Manuka Blank
X. glabratus weekly captures
LureEmissions
• Manuka:High initially,expon. decay(large surface area: volume ratio)
• Cubeb:Low initially,slow, steadyrelease(smaller surface area: volume ratio)
B
Time (d)
0 10 20 30 40 50 60 70 80
Qua
ntity
(g
)0
5
10
15
20
25
30
Time (d)
30 40 50 60 70 80
Qua
ntity
(g
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6CubebManukaα-copaene
(Kendra et al. 2015. J. Econ. Entomol.)
ConclusionsCubeb bubble lure
• More attractive than the manuka lure• Has a field life of at least 3 months, due to extended low release of sesquiterpenes
• Best product currently available for detection of RAB(and less expensive than the manuka lure)
However, cubeb lure contains a complexmixture of terpenoids; specific attractivechemicals had not been confirmed.
Further Improvement of RAB Lure(Collaboration with Synergy)
Goal = Elucidate the primary attractants in cubeb oil.
• Used fractional distillation to separate whole oil into 17 fractions (based on chemical boiling point)
• Fractions formulated as bubble lures– EAG analyses– 2‐choice bioassays
• Only 2 fractions were significantly attractive to RAB; both were high in α‐copaene and α‐cubebene
• Decided to focus on α‐copaene first
New Lure EvaluationsTwo prototype lures prepared• Copaiba oil
(9% α‐copaene, no cubebene)
• Proprietary oil product(50% α‐copaene)
12‐wk field test• Compare new lures to cubeb lure
(10% α‐copaene, 10% α‐cubebene)
Conclusions• (‐) α‐copaene = primary attractant• Increased copaene = improved lure
50% Cop Cubeb Copaiba Control
X. g
labr
atus
/ tra
p / w
k
0
2
4
6
8
10
12
14
16 a
b b
c
Week
1 2 3 4 5 6 7 8 9 10 11 12X
. gla
brat
us /
wk
0
20
40
60
80
100
120
140
160
180
50% CopCubebCopaibaControl
A
B
Kendra et al. J. Pest Sci. (in review)
THANK YOU!Sources of Funding• USDA National Plant Disease Recovery System• Florida Avocado Administrative Committee
Recent Publications• Kendra, P. E., W. S. Montgomery, J. Niogret, E. Q. Schnell, M. A. Deyrup, and N. D. Epsky. 2014.
Evaluation of seven essential oils identifies cubeb oil as most effective attractant for detection of Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae). J. Pest Sci. 87: 681‐689.
• Kendra, P. E., W. S. Montgomery, J. Niogret, G. E. Pruett, A. E. Mayfield III, M. MacKenzie, M. A. Deyrup, G. R. Bauchan, R. C. Ploetz, and N. D. Epsky. 2014. North American Lauraceae: Terpenoidemissions, relative attraction, and boring preferences of redbay ambrosia beetle, Xyleborus glabratus(Coleoptera: Curculionidae: Scolytinae). PLoS ONE 9 (7): e102086.
• Kendra, P. E., J. Niogret, W. S. Montgomery, M. A. Deyrup, and N. D. Epsky. 2015. Cubeb oil lures: Terpenoid emissions, trapping efficacy, and longevity for attraction of redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae). J. Econ. Entomol. 108: 350‐361.
• Kendra, P. E., W. S. Montgomery, M. A. Deyrup, and D. Wakarchuk. Improved lure for redbayambrosia beetle developed by enrichment of α‐copaene content. J. Pest Sci. (in review).