(11Z,13E)-hexadecadien-1-yl acetate: Sex pheromone of the grass webworm Herpetogramma licarsisalis - Identification, synthesis, and field bioassays

Article abstract of DOI:10.1007/s10886-007-9259-4

The grass webworm Herpetogramma licarsisalis (Lepidoptera: Crambidae), which has recently established in pasture in Northland, New Zealand, is an important pest of many tropical and subtropical grasses. Two pheromone components, (Z)-11-hexadecen-1-yl acet

Full text of DOI:10.1007/s10886-007-9259-4

J Chem Ecol (2007) 33:839–847
DOI 10.1007/s10886-007-9259-4
(11Z,13E)-Hexadecadien-1-yl Acetate: Sex Pheromone
of the Grass Webworm Herpetogramma licarsisalis—
Identification, Synthesis, and Field Bioassays
Andrew R. Gibb & D. Max Suckling &
Ashraf M. El-Sayed & Björn Bohman &
C. Rikard Unelius & Jennifer J. Dymock &
Michelle L. Larsen & Bruce E. Willoughby
Received: 15 August 2006 /Revised: 3 January 2007 /Accepted: 13 January 2007 /
Published online: 2 March 2007
#
Springer Science + Business Media, LLC 2007
Abstract The grass webworm Herpetogramma licarsisalis (Lepidoptera: Crambidae),
which has recently established in pasture in Northland, New Zealand, is an important pest
of many tropical and subtropical grasses. Two pheromone components, (Z)-11-hexadecen-
1-yl acetate (Z11–16:Ac) and (11Z,13E)-hexadecadien-1-yl acetate (Z11,E13–16:Ac), were
identified in pheromone gland extracts of female moths by gas chromatography (GC), GC-
electroantennographic detection, and GC-mass spectrometry in conjunction with micro-
chemical tests (dimethyldisulfide and 4-methyl-1,2,4-triazoline-3,5-dione derivatizations).
Z11,E13–16:Ac and its geometric isomer (11E,13Z)-hexadecadien-1-yl acetate (E11,Z13–
16:Ac) were synthesized via stereoselective Wittig reactions, and the identity of the diene
present in the pheromone glands was confirmed to be Z11,E13–16:Ac. Field bioassays at
Indooroopilly in Brisbane, Australia, established that Z11,E13–16:Ac was necessary and
sufficient for attraction of male grass webworm moths and that the corresponding alcohol,
(11Z,13E)-hexadecadien-1-ol (Z11,E13–16:OH), had a strong inhibitory effect on trap
catches at the ratios tested. When mixed with Z11,E13–16:Ac in various ratios, Z11–16:Ac
had no effect on the attractiveness of lures.
Electronic supplementary material The online version of this article (doi:10.1007/s10886-007-9259-4)
contains supplementary material, which is available to authorized users.
:
:
A. R. Gibb (*) D. M. Suckling A. M. El-Sayed
Horticulture and Food Research Institute of New Zealand Ltd., P.O. Box 51, Lincoln, New Zealand
e-mail: agibb@hortresearch.co.nz
:
B. Bohman C. R. Unelius
Department of Chemistry and Biomedical Sciences, University of Kalmar, 391 82 Kalmar, Sweden
J. J. Dymock
29A Seaview Road, Cable Bay, Mangonui, 0557 Northland, New Zealand
M. L. Larsen
Bugs Ed., P.O. Box 446, The Gap, Queensland 4061, Australia
B. E. Willoughby
AgResearch Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand

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J Chem Ecol (2007) 33:839–847
.
.
.
Keywords Grass webworm Herpetogramma licarsisalis Crambidae
.
.
(Z)-11-Hexadecen-1-yl acetate (11Z,13E)-Hexadecadien-1-yl acetate
(11Z,13E)-Hexadecadien-1-ol Behavioral antagonist MTAD
.
.
Introduction
The grass webworm Herpetogramma licarsisalis (Walker, 1859) (Lepidoptera: Crambidae)
is an important pest of many tropical and subtropical grasses used for pasture and orna-
mental turf. H. licarsisalis is widely distributed globally as it is present in central Africa,
Sierra Leone, Egypt, Saudi Arabia, India, Japan, Southeast Asia, Hawaii, and northern
Australia (Tashiro, 1976; Common, 1990; Goater and Knill-Jones, 1999). Infestations have
also been reported from Spain and Portugal, and the species has recently been recorded in
Britain and Sweden (Goater and Knill-Jones, 1999; Svensson, 2003).
In 1999, H. licarsisalis larvae were confirmed in kikuyu (Pennisetum clandestinum
Hochst. Ex Chiov. South) dairy pasture on the Aupouri Peninsula in Northland, New Zealand
(Hardwick et al., 2000). During the outbreak, densities of up to 1,500 caterpillars per square
meter were recorded that were associated with significant damage to kikuyu swards
(S. Hardwick, personal communication). Despite the fact that the infestation was considered
to be at the margins of the moth’s climatic and geographical range (Hardwick et al., 2000;
Willoughby and Barns, 2002; Jensen and Cameron, 2004), low-density grass webworm
populations still persist on the Aupouri Peninsula.
Our objective was to identify the sex pheromone of H. licarsisalis to use as a monitoring
tool of the existing populations for deployment in delimitation surveys and for collection of
phenological data for pest management. A pheromone attractant would also be useful as a
basis of an early warning system for any future outbreaks in the Northland area, including
the detection of new incursions from the east coast of Australia (Fox, 1978).
To date, sex pheromone attractants for more than 40 crambid moth species have been
identified (El-Sayed, 2006), but none is known from the genus Herpetogramma. We report
in this study the identification of two compounds in pheromone gland extracts of H.
licarsisalis and the evaluation of their biological activity in a series of field bioassays in
Queensland, Australia.
Methods and Materials
Insects Approximately 50 H. licarsisalis pupae were obtained from AgResearch, Ruakura
(see Jensen and Cameron, 2004 for a review). A colony was established at HortResearch,
Lincoln, and maintained for five generations at 22°C and 60% relative humidity. Freshly
emerged adults were placed in 400×600 mm polyethylene bags (one to two males and one
to two females per bag). Each of the bags was supported by a stainless steel wire frame. Each
bag contained six ‘Pioneer’ hybrid maize (Zea mays ssp. mays) seedlings on which female
moths readily deposited egg batches. Maize leaves infested with egg batches were collected
daily and placed into 680 ml plastic containers (Huhtamaki Henderson Ltd., Auckland, NZ).
After eclosion, groups of ca. 10 early-instar larvae were transferred to additional plastic
containers to avoid cannibalism. The larvae were supplied with fresh maize leaves as
required. Pupae were collected and held individually until adult emergence in 35 ml plastic
containers (Lily® portion cups with lids; Huhtamaki Henderson Ltd.). The antennae of males
were used for coupled gas chromatographic-electroantennographic detection (GC-EAD),

J Chem Ecol (2007) 33:839–847
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whereas females had their pheromone glands excised and extracted for analysis by GC-EAD,
GC, and GC-mass spectrometry (MS).
Pheromone Gland Extraction and Analyses Pheromone glands were removed from actively
calling 24- to 48-hr-old female H. licarsisalis during the third and fourth hours of the
scotophase. Excised glands were extracted in 20–40 μl of n-hexane for 5 min. The resulting
supernatant was stored at −20°C until analysis. For quantitative analysis, the pheromone
glands of 10 48-hr-old females were extracted with a 40-μl aliquot of n-hexane containing
4 ng of tetracosane as an internal standard. Two pheromone gland extracts were also
derivatized, with either 4-methyl-1,2,4-triazoline-3,5-dione (MTAD; Sigma-Aldrich, NSW,
Australia) or dimethyldisulfide (DMDS; Merck, Darmstadt, Germany), to determine the
double-bond positions of the two MS-detectable compounds that elicited EAD responses.
For the MTAD derivatization of a 26-female gland extract, we followed the procedure of
McElfresh and Millar (1999). For the DMDS derivatizations of a 96-female gland extract,
and (11Z)-hexadecen-1-yl acetate (Z11–16:Ac) and (11E)-hexadecen-1-yl acetate (E11–16:
Ac) standards, we followed the procedure described by Buser et al. (1983).
Gas Chromatography-Electroantennographic Detection We analyzed pheromone gland
extracts (five batches of 10, 13, 27, 18, and 10 pheromone glands) by GC-EAD, with a
Varian 3800 GC coupled to an EAD Recording Unit (Syntech, Hilversum, The Netherlands).
For details of the preparation of moth antennae, and our setup of associated equipment for
GC-EAD analyses, see the work of Gibb et al. (2006). Extracts were run on DB-5 (30 m×
0.25 mm i.d.×0.5 μm film; Agilent Technologies, Palo Alto, CA, USA) and DB-Wax
columns (30 m×0.25 mm i.d.×0.5 μm film; Agilent) with 1:1 split outlets. Helium was
used as the carrier gas (1 ml min−1), and injections were splitless for 0.6 min. Injector and
detector temperatures were 220° and 300°C, respectively, and the GC temperature program
was 80°C for 1 min, 10°C min−1 to 240°C, and held for 35 min. Kováts retention indexes
(KIs) (Kováts, 1965; Marques et al., 2000) were calculated for the compounds that elicited
antennal responses to compare relative retention times and, thus, to obtain rudimentary
information about the identity of the EAD-active compounds.
Gas Chromatography-Mass Spectrometry We compared the retention times and mass
spectra of the EAD-active compounds detected in a gland extract (1 μl, ca. 18-female
equivalents) with those of known standards by using a Varian 3800 GC coupled to a Varian
2200 mass spectrometer (GC-MS). Helium was used as the carrier gas (1 ml min−1), and
injections were splitless for 0.6 min. Transfer line and ion trap temperatures were 250° and
200°C, respectively. The GC injector temperature was 220°C, and the temperature program
was 100°C for 1 min, 10°C min−1 to 210°C, and held for 18 min using a VF-5ms column
(30 m×0.25 mm i.d.×0.25 μm film; Varian Inc., Walnut Creek, CA, USA). The MTAD-
and DMDS-derivatized pheromone gland extracts, and the DMDS-derivatized standards,
were also analyzed by GC-MS (injector temperature 250°C; 8 min solvent delay for MS) on
the VF-5ms column, using oven ramps of 15°C min−1 from 100° to 300°C, and held for
20 min (MTAD), or 15°C min−1 from 100° to 260°C, and held for 20 min (DMDS).
Chemicals Z11–16:Ac and E11–16:Ac (both >98% isomerically pure by GC analysis) were
obtained from Pherobank (Wageningen, The Netherlands). (10E,12Z)-Hexadecadien-1-yl
acetate (E10,Z12–16:Ac) and (10E,12Z)-hexadecadien-1-ol (E10,Z12–16:OH) were avail-
able from previous work (Suckling et al., 2005). (11Z,13E)-Hexadecadien-1-ol (Z11,E13–
16:OH) and the corresponding acetate (11Z,13E)-hexadecadien-1-yl acetate (Z11,E13–16:

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J Chem Ecol (2007) 33:839–847
Ac) were synthesized as shown in Scheme 1 and as described in detail in the online
supplement. The synthesis of (11E,13Z)-hexadecadien-1-yl acetate (E11,Z13–16:Ac) is also
described in the online supplement.
Field Bioassays We undertook a series of field bioassays in kikuyu turf at the Indooroopilly
Golf Course (27.5090° S, 152.9948° E), Brisbane, Australia (trials A, B, and C). Test
compounds, based on ratios established from GC analyses of H. licarsisalis gland extracts,
were loaded onto red rubber septa (Thomas Scientific Inc., Philadelphia, PA, USA). In all
trials, green delta traps (Clare et al., 2000) were attached to fencing wires, at a height of ca.
0.5 m, with 10 m spacings between treatments and >50 m spacings between replicates. Trap
positions within each replicate were rerandomized, and sticky inserts were replaced, at each
check for capturing male H. licarsisalis.
In trial A (April 8–28, 2005), the attraction of H. licarsisalis males to various combi-
nations of the three sex pheromone candidate compounds was investigated. Traps were
checked seven times at intervals of 1–4 d. Treatments were (1) blank control, (2) 100:0:0,
(3) 0:100:0, (4) 0:0:100, (5) 30:70:0, (6) 30:70:1, and (7) 30:70:10 μg loadings of Z11–16:
Ac, Z11,E13–16:Ac, and Z11,E13–16:OH (N = 5).
In trial B (January 24 to February 15, 2006), the attraction of H. licarsisalis males to
100 μg of Z11,E13–16:Ac was compared with the attraction of H. licarsisalis males to
binary mixes comprising 100 μg of Z11,E13–16:Ac and various doses of Z11–16:Ac. Traps
were checked six times at intervals of 1–5 d. Treatments were (1) blank control, (2) 100:0,
(3) 100:11, (4) 100:25, (5) 100:42, and (6) 100:66 μg loadings of Z11,E13–16:Ac and Z11–
16:Ac (N = 4).
Trial C was a dose response trial based on treatment 3 from trial A. Traps were checked
four times at intervals of 3 d from February 21 to March 5, 2006. Treatments were (1) blank
control, (2) 10, (3) 100, and (4) 1000 μg doses of Z11,E13-16:Ac (N = 5).
Statistical Analyses Only treatments that attracted moths were included in the statistical
analyses. For each trial, the sum of moths captured per trap was analyzed for treatment and
block effects using two-way analysis of variance (ANOVA) (MINITAB, version 14).
Residual plots were used to check the validity of the ANOVA assumptions, and square root
Scheme 1 Syntheses of (11Z,13E)-hexadecadien-1-ol (5) and (11Z,13E)-hexadecadien-1-yl acetate (6).
Reaction conditions: (a) Amberlyst 15, t-butylated hydroxyanisole (BHA), 3,4-dihydropyran, diethyl ether,
0°C to room temperature (RT); (b) PPh3, MeCN, reflux; (c) sodium ethoxide, THF, reflux then −100°C,
addition of (E)-2-pentenal, then to RT; (d) Amberlyst 15, BHA, MeOH; 45°C; (e) Ac2O/pyridine, RT

J Chem Ecol (2007) 33:839–847
843
(x + 0.5) transformations of the summed captures were undertaken to remove variance
heterogeneity. Means were compared by Fisher’s protected least-significant difference test
(P = 0.05) (MINITAB, version 14).
Results and Discussion
Identification of Gland Components Eliciting Antennal Responses In GC-EAD assays,
male H. licarsisalis antennae responded repeatedly to three compounds in pheromone gland
extracts. Only two of these compounds (X and Y, Fig. 1) were visible in the flame ionization
detector (FID) trace (KIs of 2001 and 2037, respectively, on the DB-5 column, and 2365
and 2508, respectively, on the DB-Wax column). Antennal response times were the only
indication of the presence of compound Z in the extracts. On the DB-5 column, no peak for
compound Z was visible in the FID trace, whereas on the DB-Wax column, the antennal
response time suggested that the compound was co-eluting on the tail of another unidentified
compound (Fig. 1).
The retention times of compound X on DB-5 and DB-Wax columns suggested the
presence of a monounsaturated hexadecen-1-yl acetate (Marques et al., 2000), and KIs were
identical with those of the Z11–16:Ac standard. In addition, the mass spectrum of compound
X [m/z (relative intensity—rel. int.) 222 (4), 166 (2), 137 (5), 123 (13), 109 (23), 95 (56),
81 (100), 67 (98), 61 (7), and 55 (49)] was virtually identical with that of Z11–16:Ac, and
the retention time of X was the same as the retention time of Z11–16:Ac on the VF-5ms
column. A comparison of the retention times of the DMDS adducts of Z11–16:Ac and E11–
16:Ac, with the DMDS derivatization products of a grass webworm pheromone gland
extract, unequivocally confirmed that compound X was Z11–16:Ac rather than E11–16:Ac.
Both hexadecen-1-yl acetate DMDS adducts have a molecular ion at m/z (rel. int.) 376 (7)
and diagnostic ions at m/z (rel. int.) 117 (20, [C5H10SCH3]+) and 259 (100, [O2C13H24
SCH3]+) corresponding to the addition of DMDS to a double bond at position 11.
A
EAD
Z
X
Y
FID
A
B
EAD
Z
X
B
Y
FID
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
Time (min)
Fig. 1 Coupled gas chromatogram-electroantennograms of Herpetogramma licarsisalis male antennae
responding to compounds (X = (Z)-11-hexadecen-1-yl acetate, Y = (11Z,13E)-hexadecadien-1-yl acetate, and
Z = tentatively identified as (11Z,13E)-hexadecadien-1-ol), in pheromone gland extracts (ca. 1-female
equivalents), eluting from DB-Wax (A) and DB-5 (B) columns

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J Chem Ecol (2007) 33:839–847
The retention times of compound Y on the DB-5 and DB-Wax columns suggested a C16-
conjugated dien-1-yl acetate after a comparison with a number of C16-conjugated and C16-
nonconjugated dien-1-yl acetate standards. Similarly, the antennal response time for
compound Z on the DB-5 and DB-Wax columns suggested a C16-conjugated dien-1-ol by
comparison with a number of C16-conjugated and C16-nonconjugated dien-1-ol standards.
Furthermore, the retention times of E10,Z12–16:Ac and E10,Z12–16:OH were the same as
those of compounds Y and Z, respectively. Both of these standards elicited strong EAD
signals from male grass webworm antennae, and when E10,Z12–16:Ac was added to an
aliquot of pheromone extract, it co-eluted with compound Y on both columns. However, a
trapping trial in Northland in early 2003, using these two conjugated dienes in various
combinations with Z11–16:Ac, failed to trap any moths at a time when moths were ob-
served flying (Willoughby, unpublished data).
We hypothesized that although compounds Y and Z were C16-conjugated dienes, the
diene was probably at either the 9,11 or 11,13 position. The analysis of the MTAD-deriv-
atized pheromone gland extract by GC-MS revealed an adduct with a molecular ion at m/z
(rel. int.) 393 (1), and diagnostic ions at m/z (rel. int.) 364 (21, [C19H30N3O4]+) and 194
(100, [C9H12N3O2]+), indicative of a C16 dien-1-yl acetate with the diene in the 11,13
position. Thus, compound Y was identified as an 11,13-hexadecadien-1-yl acetate. We
could not confirm the identity of compound Z due to the small amount of material in gland
extracts (not detectable by GC-FID or GC-MS), but we hypothesized that compound Z was
likely to be the C16 dien-1-ol precursor of the insect-produced C16 dien-1-yl acetate (see
Jurenka, 2004 for a review).
Stereoselective syntheses of the (Z,E) and (E,Z) isomers of 11,13-hexadecadien-1-yl
acetate were carried out. These syntheses also made the (Z,Z) and (E,E) isomers as trace by-
products, giving us access to all four stereoisomers. A comparison of the spectrum [m/z (rel.
int.) 280 (1, M+), 220 (4), 177 (3), 163 (4), 149 (8), 135 (15), 121 (27), 107 (14), 95 (43), 81
(54), 67 (100), 55 (21), and 43 (44)] and retention times of compound Y in pheromone
gland extract, with the four spectra of the 11,13-stereoisomers, unambiguously confirmed
compound Y as Z11,E13–16:Ac. Analysis of an H. licarsisalis gland extract by GC on the
DB-Wax column showed that Z11,E13–16:Ac and Z11–16:Ac were present in a ca. 70:30
ratio. The amount of Z11,E13–16:Ac and Z11–16:Ac per female was calculated to be ∼280
and 100 pg, respectively (N = 10).
Synthesis of Pheromone Compounds The synthesis of (11Z,13E)-hexadecadien-1-ol 5
(Scheme 1) and the corresponding acetate 6 (Scheme 1) started with 11-bromoundecanol 1,
which was protected using dihydropyran with Amberlyst 15 as catalyst (Santangelo et al.,
2002). The THP-protected bromide 2 was transformed to the phosphonium salt 3 with PPh3
(Legrand et al., 2004). A Wittig reaction between 3 and (E)-2-pentenal in the presence of
sodium ethoxide made, after deprotection, the (Z,E)-dien-1-ol 5 as the major product.
Acetylation of 5 using acetic anhydride in pyridine produced acetate 6 (Santangelo et al.,
2002).
Field Bioassays In the field bioassays, we established Z11,E13–16:Ac as the main sex
pheromone component of H. licarsisalis. In trial A, the treatments with Z11,E13–16:Ac as a
single component or in combination with Z11–16:Ac (treatments 3 and 5, respectively)
were equally attractive to male moths (P < 0.05) (Fig. 2a). Single-component lures loaded
with Z11,E13–16:OH were not attractive, and the addition of Z11,E13-16:OH to the binary
mix of Z11,E13-16:Ac and Z11–16:Ac was strongly inhibitory at the ratios tested (P <
0.05).

J Chem Ecol (2007) 33:839–847
845
25
20
15
10
5
Fig. 2 Mean (+SEM)
a
total catches of Herpetogramma
licarsisalis male moths at
Indooroopilly Golf Course
(Brisbane, Australia) in a blend
trial (trial A) of the three com-
pounds that elicited responses
from moth antennae (two-way
ANOVA for treatment effect,
F = 23.18; df = 5, 29;
P < 0.001, and for block effect
F = 2.9; df = 4, 29; P = 0.048,
followed by Fisher’s protected
least significant differences
(PLSD test), and in a two-
component blend trial (trial B),
using (11Z,13E)-
Aa
a
b
0
Z11,E13-16:OH
Z11,E13-16:Ac
Z11-16:Ac
-
-
-
-
-
-
100
-
-
-
70
30
1
10
100
-
70
30
70
30
100
hexadecadien-1-yl acetate and
(Z)-11-hexadecen-1-yl acetate
(two-way ANOVA for treatment
effect, F = 53.29;
df = 5, 23; P < 0.001, and for
block effect F = 5.4; df = 3, 23;
P = 0.01, followed by Fisher’s
PLSD test). Amounts on the x-axis
are micrograms per lure, and
treatments labeled with the same
letter are not significantly
different ( P> 0.05)
90
a
a
Bb
80
70
60
50
40
30
20
10
a
a
a
b
0
Z11,E13-16:Ac
Z11-16:Ac
-
-
100
-
100
11
100
25
100
100
Although we identified Z11–16:Ac from gland extracts, male grass webworm moths were
not attracted to lures loaded with this compound only. Furthermore, Z11–16:Ac, when added to
Z11,E13–16:Ac over a range of ratios, did not increase attraction to lures (P > 0.05) (Fig. 2b).
In trial C (Fig. 3), we tested the optimal dose of Z11,E13–16:Ac required for attracting
male grass webworm moths. Lures loaded with 10 μg of Z11,E13–16:Ac attracted few
moths (P < 0.05), and a 1,000-μg dose was not better than the 100-μg dose (P > 0.05).
Fig. 3 Mean (+SEM) total catches
of Herpetogramma licarsisalis
male moths to various doses of
(11Z,13E)-hexadecadien-1-yl ace-
tate (trial C) at Indooroopilly Golf
Course (Brisbane, Australia) (two-
way ANOVA for treatment effect,
F = 25.98; df = 2, 14; P < 0.001,
and for block effect F = 2.28; df =
4, 14; P = 0.149, followed by
Fisher’s PLSD test). Amounts on
the x-axis are micrograms per lure,
and treatments labeled with the
same letter are not significantly
different (P > 0.05)
25
20
15
10
5
a
a
b
0
Z 11,E 13-16:Ac
-
10
100
1000

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J Chem Ecol (2007) 33:839–847
Z11,E13–16:Ac has already been used for monitoring male grass webworm moths in the
infested area in Northland. Lures containing 100 μg of Z11,E13–16:Ac have also success-
fully attracted male grass webworm moths in Hawaii (Suckling, unpublished data), where
the insect is the major pest of turf grass (Tashiro, 1977). Although the 11,13 position for a
C16-conjugated diene has previously been reported for pheromone components of moths in
the family of Crambidae (Arai et al., 1982; Millar et al., 2002), this is the first identification
of an (11,13)-hexadecadien-1-yl acetate as a sex pheromone component of a crambid moth.
Z11,E13–16:Ac also has been found as a minor component in the pheromone glands of two
Notodontidae (Bestmann et al., 1991, 1993).
Acknowledgments We thank Julie Hackett, Peter Jones, and Kirsten Moss for the technical assistance in
rearing insects, and Barry Bunn and Dave Rogers for commenting on an earlier version of the manuscript.
Eric Jang (USDA-ARS) and his team assisted in trapping in Hawaii. Funding was provided by the New
Zealand Foundation for Research, Science, and Technology (FRST), under the “Better Border Biosecurity”
and previous programs, to develop scientific capability to respond to biosecurity incursions. We are also
grateful to the University of Kalmar, Sweden, for the additional financial support.
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