700 Invasive Stink Bugs and Related Species (Pentatomoidea)
guildinii, and Nezara viridula, although statistical comparisons to unbaited traps were not presented
(Laumann et al. 2011).
15.2.19 Tibraca limbativentris (Stål) [Pentatomidae: Pentatominae: Carpocorini]
Borges et al. (2006) isolated a male-produced sex attractant pheromone from the rice stalk stink bug,
Tibraca limbativentris, which along with Oebalus poecilus (see above), is one of two major stink bug
pests of rice in South America. Olfactometer bioassays showed that males attracted only females and
primarily at night. GC-MS analyses of headspace volatiles from males showed two male-specific
compounds on HP-1 and DB-WAX columns. The mass spectral fragmentation patterns along with
matches to spectra in the NIST MS database suggested that these compounds were stereoisomers of
1,10- bisaboladien-3-ol (= zingiberenol), which was confirmed by non-stereoselective syntheses of mix-
tures of isomers (Figure 15.15) starting from (R)- and (S)-citronellal following Hagiwara et al. (2002) in
an interesting variation of the synthesis shown in Figure 15.8.
Each synthesis produced a mixture of four stereoisomers, zingiberenol I mix from (R)-citronellal and
zingiberenol II mix from (S)-citronellal. Trimethylsilyl derivatives of all four diastereomers of zingib-
erenol were partially separated on an HP-1 GC column, but the lack of authentic standards of the indi-
vidual stereoisomers of known configuration prevented the assignment of the absolute configurations
of the two male-specific compounds. In light of more recent findings (Khrimian et al. 2014a), the faster
eluting (from an HP-1 GC column) and more abundant male-specific compound in T. limbativentris
can be assigned the cis relative configuration, and the slower eluting minor compound trans. When the
zingiberenol I and zingiberenol II mixtures were tested against each other in olfactometer bioassays,
both were equally attractive, whereas when the mixtures were compared individually with a neutral
control, only the zingiberenol II mixture derived from (S)-citronellal was attractive (Borges et al. 2006).
It remains to be seen whether T. limbativentris and Oebalus poecilus share the same diastereomer
of 1,10-bisaboladien-3-ol 50 with the (7S)-configuration (Figure 15.9) as their sex pheromone.
15.3 Allomones: Defensive Chemicals
15.3.1 Range of Chemistry
Defensive compounds of pentatomoid bugs are produced and stored in the dorsal abdominal and meta-
thoracic glands. These organs have been studied in several pentatomoid species (Pavis 1987, Aldrich
1995a, Moraes et al. 2008b, Fávaro et al. 2011) and the secretions have been analyzed from many species.
Whereas these chemicals have been implied to have defensive functions in numerous species, their puta-
tive functional roles as allomones has actually been tested in bioassays in only a few species.
The intraspecific variability in the chemistry of the secretions from nymphs and adults respectively is
generally low, and the morphology of the glands is quite conserved across species (Aldrich et al. 1978,
Pavis 1987, Aldrich 1988). In nymphs, the compounds are produced and stored in dorsal abdominal
glands (DAGs) distributed in tergites 3 and 4, 4 and 5, and 5 and 6 (Aldrich et al. 1978, Aldrich 1988). In
contrast, adults produce these compounds in the metathoracic glands (MTGs) and store them in a large
OHC
a(S)-citronellal 48 49bc
O OHOOFIGURE 15.15 Non-stereoselective synthesis of zingiberenol II mix of isomers ( 49 ), a sex pheromone of Tibraca limbati-
ventris, from (S)-citronellal. a) CH 2 =CHC(O)CH 3 / Et 2 NTMS; b) KOH/Bu 4 NOH/THF-Et 2 O; c) CH 3 Li/Et 2 O.