Decadienoates: Sex pheromone components of nettle caterpillars Darna trima and D. bradleyi

Article abstract of DOI:10.1023/A:1005561127155

This study was undertaken to identify sex pheromone components of nettle caterpillars Darna trima and Darna bradleyi (Lepidoptera: Limacodidae) whose larvae defoliate oil palm, Elaeis guineensis, in southeast Asia. Coupled gas chromatographic-electroantennographic detection (GC-EAD) analyses of pheromone gland extracts revealed two antennally active compounds produced by female D. trima and two by female D. bradleyi. Molecular structures of these candidate pheromone components were identified by electron-impact and chemical-ionization mass spectrometry; retention-index calculations on DB-5, DB-23, and DB-210 columns; microanalytical treatments, as well as syntheses of 'auxilliary' compounds that facilitated identification of the compounds. The compounds from D. trima were 2-methylbutyl (E)-7,9-decadienoate (A) and (E)-2-hexenyl (E)-7,9-decadienoate (B); from D. bradleyi we identified methyl (E)-7,9-decadienoate (C), and isobutyl (E)-7,9-decadienoate (D). In field experiments in Malaysia, (S)-2-methylbutyl (E)-7,9-decadienoate (SA) in combination with B proved to be essential and synergistic pheromone components for attraction of male D. trima. (R)-2-Methylbutyl (E)-7,9-decadienoate (RA) had no behavioral activity. Compound D singly attracted male D. bradleyi, but addition of C to D at a 1:10 ratio significantly enhanced attractiveness of the bait. Synthetic pheromone blends were more effective trap baits than unmated female moths and could be developed for monitoring populations of D. trima and D. bradleyi in Asian oil palm plantations.

Full text of DOI:10.1023/A:1005561127155

Journal of Chemical Ecology, Vol. 26, No. 8, 2000
DECADIENOATES: SEX PHEROMONE COMPONENTS OF
NETTLE CATERPILLARS Darna trima AND D. bradleyi
1
1
1,
YORIANTA SASAERILA, REGINE GRIES, GERHARD GRIES, *
1
1
2
GRIGORI KHASKIN, SKIP KING, and TEO CHOR BOO
1Centre for Environmental Biology, Department of Biological Sciences
Simon Fraser University
Burnaby, British Columbia V5A 1S6, Canada
2Applied Agricultural Research
Sendirian Berhad, Sungai Buloh, Malaysia
(Received December 2, 1999; accepted April 15, 2000)
Abstract—This study was undertaken to identify sex pheromone components
of nettle caterpillars Darna trima and Darna bradleyi (Lepidoptera:
Limacodidae) whose larvae defoliate oil palm, Elaeis guineensis, in southeast
Asia. Coupled gas chromatographic–electroantennographic detection (GC-
EAD) analyses of pheromone gland extracts revealed two antennally
active compounds produced by female D. trima and two by female D.
bradleyi. Molecular structures of these candidate pheromone components
were identified by electron-impact and chemical-ionization mass spectrometry;
retention-index calculations on DB-5, DB-23, and DB-210 columns; micro-
analytical treatments, as well as syntheses of “auxilliary” compounds that
facilitated identification of the compounds. The compounds from D. trima
were 2-methylbutyl (E)-7,9-decadienoate (A) and (E)-2-hexenyl (E)-7,9-
decadienoate (B); from D. bradleyi we identified methyl (E)-7,9-decadienoate
(
(
C), and isobutyl (E)-7,9-decadienoate (D). In field experiments in Malaysia,
S)-2-methylbutyl (E)-7,9-decadienoate (SA) in combination with B proved
to be essential and synergistic pheromone components for attraction of male
D. trima. (R)-2-Methylbutyl (E)-7,9-decadienoate (RA) had no behavioral
activity. Compound D singly attracted male D. bradleyi, but addition of C to
D at a 1 : 10 ratio significantly enhanced attractiveness of the bait. Synthetic
pheromone blends were more effective trap baits than unmated female moths
and could be developed for monitoring populations of D. trima and D. bradleyi
in Asian oil palm plantations.
Key Words—Lepidoptera, Limacodidae, Darna trima, Darna bradleyi,
Setothosea asigna, Setora nitens, nettle caterpillars, oil palm, sex phero-
*
To whom correspondence should be addressed. e-mail: gries@sfu.ca
1
969
0
098-0331
/
00
/
0800-1969$18.00
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0  2000 Plenum Publishing Corporation

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SASAERILA ET AL.
mone, 2-methylbutyl (E)-7,9-decadienoate, (E)-2-hexenyl (E)-7,9-decadien-
oate, methyl (E)-7,9-decadienoate, isobutyl (E)-7,9-decadienoate, (E)-9-
dodecenal, (E)-9,11-dodecadienal, (Z)-9-dodecenal, (Z)-9,11-dodecadienal.
INTRODUCTION
The nettle caterpillars Darna trima and D. bradleyi as well as Setora nitens and
Setothosea asigna (Cock et al., 1987) (Lepidoptera: Limacodidae) are impor-
tant lepidopteran pests in southeast Asian oil palm plantations. D. trima and
D. bradleyi caused severe defoliation of palms in Peninsular Malaysia (Wood,
1
968), Sabah (Conway and Tay, 1969), Sarawak (Wan, 1972), and Sumatra
(
Turner and Gillbanks, 1974). Heavy defoliations with >2000 and 16,000 cater-
pillars of D. trima and D. bradleyi, respectively, per frond resulted in significant
reduction of fruit bunch production the following year (Wood et al., 1976). The
increase of populations is associated with prolonged dry weather, caused by El
Nino. Recurring severe outbreaks provoked efforts to control these insects (Wood
˜
et al., 1976; Chung et al., 1995; Ang et al., 1998), but little is known yet about
their behavioral and chemical ecology. We report the identification and field test-
ing of pheromone components of D. trima and D. bradleyi.
METHODS AND MATERIALS
Experimental Insects and Laboratory Analyses
Pupae of D. trima and D. bradleyi were collected in KDC-Taiko commer-
cial oil palm plantations, Sabah, Malaysia, placed separately in filter-paper-lined
Petri dishes, and kept at a natural 12L : 12D photoperiod. Emergent male and
female moths were separated to prevent mating. Abdominal tips with pheromone
glands of 2-day-old female D. trima and D. bradleyi were removed from females
exhibiting calling behavior shortly before and after the onset of the scotophase.
Pheromone glands were extracted for 5 min in HPLC-grade hexane, and gland
extracts and male pupae of D. trima and D. bradleyi were sent to Simon Fraser
University (SFU).
For each species, aliquots of one female equivalent (FE) of pheromone
extract were analyzed by coupled gas chromatographic-electroantennographic
detection (GC-EAD) (Arn et al., 1975) in a Hewlett Packard 5890A gas chro-
matograph equipped with three fused silica columns (30 m × 0.25 or 0.32 mm
ID) coated with DB-5, DB-23, or DB 210 (J&W Scientific, Folsom, California
9
5630-4714). Recordings were made from a male antenna suspended between
two glass capillary electrodes filled with saline solution (Staddon and Everton,

DECADIENOATES IN NETTLE CATERPILLARS
1971
1
980). The voltage of antennal responses was amplified by a custom-built ampli-
fier with a passive low-pass filter and a cut off frequency of 10 kHz.
Coupled GC-mass spectrometry in electron impact (EI) and chemical-ion-
ization (CI) modes of insect-produced and synthetic compounds employed a Var-
ian Saturn II ion trap and a Hewlett Packard 5890A fitted with a DB-5 column.
Synthetic candidate pheromone components were further subjected to GC-EAD
analyses to compare their EAD activity with those of female-produced com-
pounds.
Syntheses
(R)-2-Methylbutanol [(R)-4, Figure 1 (scheme 1)]. (S)-2-Methylbutanol
was purchased (Sigma-Aldrich). (R)-2-Methylbutanol [(R)-4] was synthesized
by modifying the method of Guoqiang et al. (1984). L-Proline methyl ester (1)
was reacted with 2-methylbutyryl chloride to afford the methyl ester of 2-methyl-
butyryl pyrrolidine (2), which in turn was converted to the corresponding dia-
stereomeric tertiary alcohol (3). Separation of the diastereomers of 3 by repeti-
tion flash chromatography was monitored by GC and NMR analyses (Guoqiang
et al., 1984). Treatment of (R)-3 with HCl and LiAlH4 gave the target (R)-4.
Enantiomeric excess (ee) of (R)-4 is assumed to be 95% based on the ee of (R)-
3
. NMR-data of (R S)-2 and (R S)-3 were in agreement with those previously
/
/
reported (Guoqiang et al., 1984). GC mass spectrometric (MS) data [m z (rela-
tive intensity)] for (R S)-2 were: 213 (5), 185 (6), 153 (9), 128 (12), 70 (100),
5
/
/
7 (20), and 41 (28); and GC-MS data for (R S)-3 were: 214 (14), 196 (7), 155
/
(25), 140 (34), 127 (44), 113 (22), 70 (100), 59 (15), 57 (27), and 41 (38).
Pheromone esters [11a–f; Figure 1 (scheme 2)]. Alkylation of 3-sulfo-
lene (5) (Sigma-Aldrich, Oakville, Ontario, Canada) with O-tetrahydropyrano-
-iodo-1-hexanol (6), prepared from 1,6-hexanediol (Sigma-Aldrich), afforded 7
scheme 2 of Figure 1) (Yamada et al., 1983; Sasaerila et al., 1997). Subsequent
6
(
extrusion of SO2 gave the diene 8, which was treated with trifluoroacetic acid in
methanol to remove the tetrahydropyranyl group, yielding (E)-7,9-decadien-1-ol
(
9). Alcohol 9 was then oxidized with pyridinium dichromate (PDC) to (E)-7,9-
1
decadienoic acid (10); H NMR (CDCL3) ppm; 81.3–1.45 (4H, m); 1.62 (2H,
quintet; J 7); 210 (2H,9, J 8); 2.33 (2H, t, J 7); 4.94 (H, d, J 11),
5
.01 (H, d, J 18), 5.67 (H, m) 6.04 (H, dd, 15 J 18.10) 6.30 (H, dt, J
8.8). The acid 10 was coupled with (S)-2-methylbutanol, (R)-2-methylbu-
1
tanol (scheme 1), 2-methylbutanol (Sigma-Aldrich), (E)-2-hexen-1-ol (Sigma-
Aldrich), methanol (Caledon Laboratories Ltd., Georgetown, Ontario, Canada)
and isobutanol (Sigma-Aldrich) to yield corresponding esters 11a–f (scheme 2),
1
H NMR spectra of 11a–f revealed the same data as the acid 10 plus additional
spectroscopic information specific to each ester, as follows: 11a, 11b, and 11c,
1
[
H NMR (CDCC3) ppm]: 0.9 (6H, m) 1.7 (H, m) 3.85 (1H, AB quartet) 3.95

1
972
SASAERILA ET AL.
FIG. 1. Schemes for the syntheses of (R)-2-methylbutanol (scheme 1) and pheromone
esters A–D (scheme 2).
(
1H, AB quartet); 11d: 0.90 (3H, t, J 7) 1.45–1.3 (2H, m) 2.0 (2H, q, J 8)
4
0
.50 (2H, d, J 7) 5.55 (H, m) 5.75 (H, m); 11e: 3.65 (3H, J 5); and 11f:
.92 (6H, d, J 7) 1.90 (H, 2 septet, J 7), 3.84 (2H, d, J 7).
Field Experiments
Experiments were conducted in commercial oil palm plantations in
Sandakan-Sabah, Malaysia. Self-made sticky delta traps (Gray et al., 1984) were
suspended from oil palms ∼1.5–2 m above ground in randomized complete
blocks, with spacings of 15–20 m. Traps were baited with grey sleeve stop-
pers (The West Company, Lionville, Pennsylvania) impregnated with candidate
pheromone components in HPLC-grade hexane. Experiments 1–4 tested three

DECADIENOATES IN NETTLE CATERPILLARS
1973
candidate pheromone components for D. trima: (S)-2-methylbutyl (E)-7,9-deca-
dienoate (SA), (R)-2-methylbutyl (E)-7,9-decadienoate (RA), and (E)-2-hexenyl
(
(
E)-7,9-decadienoate (B). Experiment 1 tested B in combination with either RA
125 mg), SA (125 mg), RA plus SA, or racemic A (250 mg). Experiment 2 tested
B (250 mg) alone and in combination with SA at 5, 25, 125, and 250 mg. Experi-
ment 3 tested SA (250 mg) and B (250 mg) singly and in combination at 1 : 1 and
1
: 0.1 ratios. Experiment 4 tested attractiveness of SA plus B at various doses
versus that of virgin female D. trima. Each female moth in this experiment was
confined in a screened cylindrical cage (3 × 5 cm) in the middle of the delta
trap and was sustained with a sugar–water-drenched cotton ball.
Experiments 5–9 assessed candidate pheromone components for D.
bradleyi: methyl (E)-7,9-decadienoate (C) and isobutyl-(E)-7,9-decadienoate
(
D). Experiment 5 tested C (250 mg) and D (250 mg) alone and in combina-
tion at a 1 : 2 ratio. Experiment 6 tested D (250 mg) alone and in combination
with C at 2.5, 25, 125, and 250 mg. Experiment 7 tested C (250 mg) singly and
in combination with D at 2.5, 25, 125 and 250 mg. Experiment 8 tested C (250
mg) alone and in combination with D (25 mg). Experiment 9 tested attractive-
ness of C plus D at a 1 : 10 ratio and different doses versus that of virgin female
D. bradleyi. As in experiment 4, female moths were confined individually in a
screened cylindrical cage. Voucher specimens of captured male D. trima and D.
bradleyi were deposited in the entomological collection at SFU.
Statistical Analysis
Various treatments in several experiments did not attract any male moths.
Despite transformation, trap catch data were not normally distributed and thus
were analyzed by nonparametric analyses of variance (Friedman’s test) followed
by comparison of means by Bonferroni (Dunn) t test (Zar, 1984; SAS STAT,
/
1
988). In all analyses, a 0.05.
RESULTS AND DISCUSSION
Laboratory Analyses
GC-EAD analyses (Figure 2) revealed two antennally active compounds in
pheromone gland extracts of female D. trima (A, B), and two others in female
D. bradleyi (C, D). Retention indices on DB-23, DB-5, and DB-210 columns of
compounds A (2109, 1676, 1996), B (2301, 1810, 2112), C (1789, 1350, 1645),
and D (1990, 1572, 1884) suggested that all four candidate pheromone com-
ponents had an ester functionality. EI mass spectra of these compounds (Figure
3
) supported an ester functionality and disclosed structural similarities between
compounds. For example, fragmentation ion m z 150 of compounds A, C, and
/

1
974
SASAERILA ET AL.
FIG. 2. Flame ionization detector (FID) and electroantennographic detector (EAD: male
moth antenna) responses to one female equivalent of pheromone gland extract, chro-
matographed on a DB-5 column; temperature program: 1 min at 100 C, 10 C min to
/
2
00 C.
D was indicative of the same diunsaturated carbonyl ion.
CI (isobutane) mass spectrometry indicated a molecular weight for com-
pounds A–D of 238, 250, 182, and 224, respectively. Compound B with molec-
ular weight 250 instead of 252 suggested an additional double bond in the C6
alcohol part of the ester. GC-CI-MS results provided evidence that the acyl ion
of compounds A–D was coupled with a C5, C6, C1, and C4 alcohol, respec-
tively. Similarly, EI mass spectra of hydrogenated A–D suggested molecular
structures identical or similar to amyl, hexyl, methyl, and butyl esters, respec-
tively, of decanoic acid. Synthetic decanoic acid methyl ester had GC retention

DECADIENOATES IN NETTLE CATERPILLARS
1975
FIG. 3. Full-scan electron impact mass spectrum of (S)-2-methylbutyl (E)-7,9-deca-
dienoate (SA), (E)-2-hexenyl (E)-7,9-decadienoate (B), methyl (E)-7,9-decadienoate (C),
and isobutyl (E)-7,9-decadienoate (D), obtained with a Varian Saturn II Ion Trap GC-MS.
and mass spectrometric characteristics identical to insect-produced hydrogenated
C. To determine the molecular structure of hydrogenated A, B, and D, decanoic
acid was esterified with all possible C6, C5, and C4 alcohols, respectively. Com-
parative GC-MS analyses of all coupling products determined that saturated A,

1
976
SASAERILA ET AL.
B and D were 2-methylbutyl, hexyl, and isobutyl esters, respectively, of decanoic
acid.
The two double-bond positions in the acyl ion of insect-produced A–D were
determined by esterifying (E)- and (Z)-3- to 8-decenoic acids with 2-methylbu-
tanol (Figure 1, scheme 1) (the alcohol part of ester A), and by GC-EAD analyses
of the resulting esters. Male D. trima antennae as representative electroantenno-
graphic detectors in these analyses responded only to (E)-7- and (Z)-7-decenoic
acid 2-methylbutyl esters, suggesting that C-7 is a double-bond position in the
acyl ion of A–D. The second double bond was hypothesized to be D9 because
retention indices of A, B, C, and D required molecules with conjugated double
bonds, and neither (E)- nor (Z)-5- decenoic acid esters were EAD active. Syn-
thetic 2-methylbutyl-, methyl-, and isobutyl (E)-7,9-decadienoate, respectively,
had retention indices, mass spectrometric, and EAD characteristics comparable
to insect-produced A, C, and D. The third double-bond position in hexenyl (E)-
7
6
,9-decadienoate (B) was determined by coupling (E)-7,9-decadienoic acid with
-hexen-1-ol and all other possible (E)- and (Z)-hexen-1-ols. Only (E)-2-hex-
enyl (E)-7,9-decadienoate had GC and GC-MS characteristics consistent with
those of D. trima-produced B.
Field Experiments
Traps baited with B in combination with either SA, SA plus RA, or racemic
A captured significant numbers of male D. trima (Figure 4, experiment 1). The
absence or presence of RA in trap baits did not affect captures of male moths,
indicating that this compound is behaviorally benign, and likely not produced by
female D. trima. Singly, compound SA failed to attract substantial numbers of
male moths (Figure 4, experiment 3), providing strong evidence that SA and B
are essential and synergistic pheromone components of D. trima. Blend ratios of
SA and B (1 : 2 or 1 : 1) resembling those in pheromone gland extracts (Figure
2
) were significantly more attractive to male D. trima (Figure 4, experiments 2
and 3).
The synthetic equivalent of most EAD-active D (Figure 2) singly attracted
male D. bradleyi (Figure 5, experiments 6–8). Deletion of D from, or its presence
in low quantity in the binary blend of C plus D greatly reduced blend attractive-
ness, supporting the contention that D is the major pheromone component of
D. bradleyi. Compound C in admixture with D at a wide (1 : 10) but not narrow
(1 : 1) blend ratio enhanced blend attractiveness (Figure 5, experiments 6 and 8),
indicating that C is a second pheromone component of D. bradleyi.
Esters A and B in D. trima and C and D in D. bradleyi are reported for the
first time as pheromone components in the Lepidoptera. With pheromone blends
identified for the limacodids Setothosea asigna (Zagatti et al., 1993; Sasaer-
ila et al., 1997) and Setora nitens (Sasaerila et al., 2000) as well as D. trima

DECADIENOATES IN NETTLE CATERPILLARS
1977
FIG. 4. Male D. trima captured (mean ± SE) in sticky 2-liter delta traps in experiments
–4; 10 replicates; August 23–December 16, 1997, Tawau, Malaysia. Bars with the same
1
letter superscript are not different; nonparametric analysis of variance by ranks (Fried-
man’s test) followed by comparison of means [Bonferroni (Dunn) t test, P < 0.05]
(
SAS STAT, 1988).
/
and D. bradleyi (this study), structural relationships among pheromone compo-
nents become apparent (Figure 6). All of the above species employ pheromone
blends with two synergistic components. The recurrence of (E)-7, (E)-9, (Z)-
9
, and D11 double bonds in dodecenal, dodecadienal, and or decadienoic acid
/

1
978
SASAERILA ET AL.
FIG. 5. Male D. bradleyi captured (mean ± SE) in sticky 2-liter delta traps in experi-
ments 5–7; 10 replicates; August 22–September 14, 1997, and experiments 8 and 9; 10
replicates; September 28–December 16, 1997, Tawau, Malaysia. Bars with the same let-
ter superscript are not different; nonparametric analysis of variance by ranks (Friedman’s
test) followed by comparison of means [Bonferroni (Dunn) t test, P < 0.05] (SAS STAT,
/
1
988).
ester pheromone components implies related biosynthetic pathways. Heterogen-
ers Setothosea asigna and Setora nitens with aldehydic pheromone components
phylogenetically may be more closely related to each other than to ester-pro-
ducing D. trima or D. bradleyi. This hypothesis, however, is yet to be tested by

DECADIENOATES IN NETTLE CATERPILLARS
1979
FIG. 6. Comparison of pheromone components of Setothosea asigna [(E)-9-dodecenal
and (E)-9,11-dodecadienal] (Zagatti et al., 1994; Sasaerila et al., 1997), Setora nitens [(Z)-
9
-dodecenal and (Z)-9,11-dodecadienal] (Sasaerila et al., 2000), Darna trima [2-methyl-
butyl (E)-7,9-decadienoate and (E)-2-hexenyl (E)-7,9-decadienoate] (this study) and D.
bradleyi [methyl (E)-7,9-decadienoate and isobutyl (E)-7,9-decadienoate] (this study).
molecular genetic analyses.
Because synthetic pheromone lures are available for S. asigna, S. nitens, D.
trima, and D. bradleyi, pheromone-based reproductive isolating mechanisms of
these coseasonal limacodids can now be investigated. Moreover, when compared
to the attractiveness of conspecific virgin females, we believe that the respec-
tive synthetic pheromone blends could be used reliably to monitor limacodid
populations.
Acknowledgments—We thank Chew Poh Soon, Lim Eng Kee, D. Subramanyam, and Ang Ban
Na (Applied Agricultural Research Sdn. Bhd.), C. Donough and Harry (IJM Corp., Sabah, Malaysia)
for field assistance and for permitting experimentation in their oil palm estates. We also thank K.
N. Slessor and the Department of Chemistry, SFU, for providing laboratory space for the syntheses,

1
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SASAERILA ET AL.
and J. H. Borden for review of the manuscript. This research was supported, in part, by an East-
ern Indonesia University Development Project (EIUDP) of the Canadian International Development
Agency (CIDA) to Y.S. and by a research grant from the Natural Sciences and Engineering Research
Council of Canada (NSERC) to G.G.
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