Semiochemistry of Pentatomoidea 701
orange reservoir (Aldrich 1988, Pavis 1987). The DAGs are not functional in most adults. There is no
apparent sexual dimorphism in the MTGs or DAGs of phytophagous pentatomids.
The chemistry of the allomones produced by pentatomoids is in most cases rather simple. In nymphs,
the principal components are short chain (E)-2-alkenals, 4-oxo-(E)-2-alkenals (C 6 , C 8 , C 10 ) and linear
hydrocarbons (mainly C 11 to C 13 ), and the production of these compounds changes with the nymphal
instar. Usually, the first instars produce 4-oxo-(E)-2-decenal in relatively large proportions, whereas
production in the second to fifth instars is reduced or even eliminated, and, instead, 4-oxo-(E)-2-hexenal
and 4-oxo-(E)-2-octenal are produced in larger quantities (Borges and Aldrich 1992). The (Z)-isomers
of 4-oxo-(E)-2-alkenals and (E)-2-alkenals also frequently are found in trace quantities in the secre-
tions of nymphs and adults (Pareja et al. 2007). In the adults, the allomones are composed of the same
compounds found in the later nymphal instars, with tridecane being the major compound. Adults also
produce short-chain alcohols (C 6 -C 8 ) and their esters, such as (E)-2-hexenyl, (E)-2-octenyl, and (E)-2-
decenyl acetates and, depending on species, a variety of other minor compounds including monoter-
penes, long-chain saturated and unsaturated aldehydes, diols, and pyrazines.
The stink bugs Edessa rufomarginata (De Geer) and E. meditabunda (subfamily Edessinae), differ
from this general pattern. In these species, the major hydrocarbon is undecane instead of tridecane in
both nymphs and adults, and the first instar does not produce 4-oxo-(E)-2-decenal (Borges and Aldrich
1992, Zarbin et al. 2012). Other pentatomids, such as Tibraca limbativentris and Euschistus heros, pro-
duce aldehydes with longer chains (e.g., tetradecanal) and E. heros also has the monoterpene linalool in
its MTG secretions (Pareja et al. 2007). Linalool also has been found in DAG extracts of adult Dichelops
melacanthus (Dallas) of both sexes (M.C.B.M., unpublished data).
Although stink bugs share a number of compounds in their allomonal blends, careful analytical studies
with robust statistical analyses have shown that these blends can be quite complex, with species-specific
differences in minor compounds and significant differences in ratios among compounds (Aldrich et
al. 1996, Pareja et al. 2007, Fávaro et al. 2011). For example, for five neotropical pentatomid species
(Euschistus heros, Dichelops melacanthus, Chinavia ubica, Chinavia impicticornis, and Piezodorus
guildinii), the fifth instars and adults shared several allomonal compounds. However, a multivariate
analysis was able to group the species according to their taxonomic relationships, with the two Chinavia
species grouped together, and D. melacanthus and E. heros grouping together (Pareja et al. 2007). For
these five species, the main compounds responsible for the separation of the adults were aldehydes and
esters, with the Chinavia species producing higher amounts of (E)-2-decenal and the analogous ester
(E)-2-decenyl acetate, whereas (E)-2-octenal and (E)-2-octenyl acetate were relatively more abundant in
E. heros and D. melacanthus (Pareja et al. 2007).
Some pentatomids produce defensive compounds with more complex chemistry. For example,
Murgantia histrionica adults produce (E)-2-octenal, (2E,6E)-2,6-octadienal and (2E,6E)-2,6-octadien-
1,8-diol from the MTGs and 2-sec-butyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine from
the prothoracic fluid (Aldrich et al. 1996). Diols and unsaturated aldehydes also were identified from the
MTG extracts of Eurydema ventralis (Kolenati), Eocanthecona furcellata, Euschistus heros, Chinavia
impicticornis, Chinavia ubica, Dichelops melacanthus, and Pallantia macunaima (Aldrich et al. 1996,
Ho et al. 2003, Pareja et al. 2007, Fávaro et al. 2011) but in tiny quantities. The roles of these compounds
as possible mediators of behavior remain to be determined.
Fávaro et al. (2012) conducted a study of the possible defensive compounds from Agroecus griseus
of different life stages. The compounds found in the DAGs of nymphs were similar to those of other
pentatomids and included (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, dodecane, (E)-2-decenal,
1-tridecene, (Z)-4-tridecene, tridecane, 4-oxo-(E)-2-decenal, and tetradecanal (Fávaro et al. 2012, 2013).
A significant difference between exuvial extracts of different nymphal stadia was the presence of (E)-2-
decenal and (E)-4-oxo-2-hexenal in the first instars and the absence of these chemicals in later instars,
which parallels DAG contents of other pentatomids (Borges and Aldrich 1992). 4-Oxo-(E)-2-decenal also
is known to mediate the aggregation behavior of first instars of several pentatomid species (Pavis et al.
1994, Fucarino et al. 2004). Analysis of the MTG content of A. griseus revealed aldehydes, hydrocarbons,
esters, oxoalkenals, and two new compounds identified as (S)-2-methylbutyl acetate and 3-methyl-2-butenyl
acetate (Fávaro et al. 2012). The absolute configuration of the former was established by GC analysis
on an enantioselective column. The biological functions of these compounds have not been determined.