Semiochemistry of Pentatomoidea 705
(Moraes et al. 2008a). Thus, it remains uncertain whether the parasitoid responds to this compound
as a cue directly associated with its host or as a means of finding the habitat of its host. Analogously,
Trissolcus basalis ( Wol la ston) was attracted to (E)-2-decenal, a compound produced by its preferred
host, Nezara viridula, in laboratory bioassays (Mattiacci et al. 1993). In another example, T. podisi
and Tr. basalis are generalist parasitoids, but field observations in soybean fields showed high rates of
Tr. basalis parasitism of N. viridula eggs, whereas T. podisi preferred E. heros eggs (Corrêa-Ferreira and
Moscardi 1995, Medeiros et al. 1998, Pacheco and Corrêa-Ferreira 2000). Laboratory experiments using
a multiple-host choice bioassay confirmed these field observations (Sujii et al. 2002). The allomones
produced by the two stink bug species may be involved in this preference. However, when individuals of
Telenomus sp. from an American population were offered two different odor sources, eggs treated with
(E)-2-decenal or (E)-2-octenal, of which the latter is produced by E. heros, the parasitoids preferred the
former odor (Borges and Aldrich, 1994). A subsequent study with Brazilian populations of Tr. basalis
and T. podisi showed that each species recognized the allomones produced by their preferred hosts.
Thus, in Y-olfactometer bioassays, Tr. basalis responded preferentially to (E)-2-decenal and 4-oxo-(E)-
2-hexenal, whereas T. podisi preferred (E)-2-hexenal and 4-oxo-(E)-2-hexenal, as predicted. The lack of
response of the Telenomus sp. American population to (E)-2-octenal remains to be clarified. One hypoth-
esis is that Telenomus sp. learned to recognize E. heros through (E)-2-hexenal, which is produced by
this stink bug, rather than through (E)-2-octenal. Despite some uncertainties as to the exact compounds
which are attractive to the various species and populations, these results overall support the hypothesis
that (E)-2-alkenals are important cues used by platygastrid parasitoids and other natural enemies to
locate their preferred hosts (Borges and Aldrich 1992, Aldrich 1994b, Pareja et al. 2007, Laumann et al.
2009). In fact, recent field experiments showed that soybean crops treated with (E)-2-hexenal attracted
higher numbers of natural enemies, mainly T. podisi , compared with untreated areas (Vieira et al. 2014).
Aldrich (1985) reported that an egg parasitoid can use the sex pheromone produced by male stink
bugs to locate females and, indirectly, the stink bug eggs. This strategy apparently is used by Telenomus
calvus (Ashmead), which exploits pheromones produced by male Podisus maculiventris and P. neglectus
(Westwood) as an indirect mechanism to locate Podisus eggs (Aldrich 1995a). This parasitoid requires
eggs less than 12 hours old to successfully develop, and so it needs a reliable method of locating fresh
eggs. The pheromone blends of male Podisus maculiventris and P. nigrispinus (Dallas) (= P. connexivus)
both contain (E)-2-hexenal, benzyl alcohol, and α-terpineol, providing a reliable cue for the wasp.
Telenomus podisi is one the main egg parasitoids of pentatomids, using different host-related cues
to locate host eggs. In Brazil, T. podisi is the most abundant natural enemy of E. heros in soybean
crops, with >80% parasitism of host eggs (Pacheco and Corrêa-Ferreira 2000, Michereff et al. 2014).
In field experiments using traps baited with E. heros pheromone (1 mg per trap of racemic methyl
2,6,10- trimethyltridecanoate), two egg parasitoids were attracted, T. podisi and Trissolcus urichi
(Crawford) (Borges et al. 1998, 2011). Laboratory experiments confirmed that T. podisi was attracted
to synthetic racemic methyl 2,6,10-trimethyltridecanoate (Silva et al. 2006). Recently, Tognon and co-
workers (2014) reported that T. podisi also is attracted to the male-produced pheromone of the rice stink
bug Tibraca limbativentris, which consists of the sesquiterpenoid zingiberenol, with a completely differ-
ent structure than the E. heros pheromone. Thus, T. podisi appears to possess a high degree of plasticity
in its recognition of a variety of chemical structures associated with hosts, responding to the simple
molecules found in the defensive secretions, such as (E)-2-alkenals and 4-oxo-(E)-2-alkenals, as well as
to more complex structures such as the long-chain methyl esters (C 10 to C 15 ) and sesquiterpenoids that
constitute the male-produced aggregation pheromones (Aldrich 1985, Borges et al. 1998, Laumann et al.
2009, Michereff et al. 2013).
In addition to volatile allomones from DAGs and MTGs, and pheromones, natural enemies may also
exploit less volatile and nonvolatile components of the cuticular lipids of stink bugs, such as long-chain
hydrocarbons (Blomquist and Bagnères 2010). For example, Colazza et al. (2007) reported that non a-
decane is present in the cuticular profile of male but not female Nezara viridula. The authors suggested
that this information may be used by egg parasitoids to distinguish residues left by male or female bugs.
In addition, Borges et al. (2003) showed that the egg parasitoid T. podisi from a Brazilian population can
recognize “footprints” from Euschistus heros females, whereas T. podisi from an American population
cannot. More recently, Salerno et al. (2009) showed that Trissolcus brochymenae (Ashmead) prefers the