692 Invasive Stink Bugs and Related Species (Pentatomoidea)
suggest that a combination of relatively inexpensive semiochemicals could be used for detection, moni-
toring, and potentially control of this polyphagous invasive pest.
However, in a study in which commercial pyramid traps baited with methyl (2E,4E,6Z)-2,4,6-
decatrienoate lures were tested in community gardens infested with H. halys, more bugs and greater
damage were noted on tomato fruits near the traps (Sargent et al. 2014). Thus, judicious placement of
traps some distance away from susceptible crops may be essential to prevent these unwanted effects.
15.2.10 Murgantia histrionica (Hahn) [Pentatomidae: Pentatominae: Strachiini]
The harlequin bug, Murgantia histrionica, is a pest of cole crops and related plants in the mustard family
in the southern United States. Zahn et al. (2008, 2012) reported that sexually mature male M. histrionica
produce an aggregation pheromone (dubbed murgantiol), which they identified as one of the stereoiso-
mers of 10,11-epoxy-1-bisabolen-3-ol ( 51 ).^1 H and^13 C NMR spectra of murgantiol isolated from extracts
of volatiles from males confirmed the proposed structure but did not determine the relative and absolute
configurations of the four chiral centers in murgantiol. A relatively short and nonstereoselective synthe-
sis of murgantiol from (S)-citronellal (Zahn et al. 2008) is shown in Figure 15.8.
Thus, (S)-citronellal was converted to cyclohexenone 48 via a tandem Michael addition/Robinson ring
annulation (~1:1 mixture of diastereomers) following Chavan et al. (1997). Addition of methyllithium to
enone 48 afforded a 38:62 mixture of less/more polar diastereomers 51, which were separated by silica gel
chromatography. Each pair of stereoisomers then was epoxidized with m-chloroperbenzoic acid to afford
binary mixtures of less and more polar diastereomeric epoxybisabolenols 52. The synthesis was repeated
with (R)-citronellal to afford the four diastereomeric epoxybisabolenols 52 with the (7R)-configuration.
The GC retention time of the male-specific compound isolated from M. histrionica matched that of one
of the less polar stereoisomers of 52 , which were subsequently shown to have the cis relative configura-
tion for the 1,4 substituents on the cyclohexene ring (Khrimian et al. 2014a). In Y-tube bioassays, female
M. histrionica responded to compounds derived from both enantiomers of citronellal, further complicat-
ing the stereochemical assignment (Zahn et al. 2008). Khrimian et al. (2014b) repeated the collection
of the male-produced volatiles of M. histrionica and discovered that they consisted of not one but two
diastereomers of 10,11-epoxy-1-bisabolen-3-ol using two enantioselective columns, Chiraldex G-TA and
Hydrodex β-6TBDM. Synthesis of all sixteen stereoisomers of 10,11-epoxy-1-bisabolen-3-ol allowed
structural determination of the two components of the M. histrionica male-produced volatiles as the
(3S,6S,7R,10S)- and (3S,6S,7R,10R)-stereoisomers 37 and 44 produced in a 1.4:1 ratio (see above under
H. halys, and Figure 15.7) (Khrimian et al. 2014b).
In field trials, Weber et al. (2014b) demonstrated significant attraction of both sexes and nymphs to col-
lard (Brassica oleracea L., acephala group) plants baited with either pheromone component compared
to plants with no lure added. The combination of the two stereoisomers 37 and 44 was most attractive to
OHC
a(S)-citronellal ent- 11 48 5152OObcHOd HOOFIGURE 15.8 Synthesis of Murgantia histrionica pheromone (murgantiol) as a mixture of diastereomers from
(S)-citronellal. a) HCHO/Piperidine; b) CH 3 COCH 2 COOCH 3 /CH 3 ONa; c) CH 3 Li; d) m-CPBA/NaHCO 3.