702 Invasive Stink Bugs and Related Species (Pentatomoidea)
15.3.2 Effect of MTG and DAG Secretions against Natural Enemies
The deterrent effects of the chemicals produced by the DAGs and MTGs of stink bugs have been dem-
onstrated in a few cases. For example, Noge et al. (2012) evaluated the effect of some possible defen-
sive compounds of Euschistus biformis, including (E)-2-hexenal, (E)-2-octenal, (E)-2-octenyl acetate,
4-oxo-(E)-2-hexenal and (E)-2-hexenyl acetate, against the praying mantis Tenodera aridifolia sinensis
(Saussure) (Mantodea: Mantidae). The compounds were evaluated individually and as blends in arena
bioassays, and it was reported that (E)-2-hexenal, (E)-2-octenal, and (E)-2-octenyl acetate were repellent
to the mantis (Noge et al. 2012). Eliyahu et al. (2012) evaluated the function of several possible defensive
compounds from pentatomid nymphs against the jumping ant Harpegnathos saltator (Hymenoptera:
Formicidae), hypothesizing that 4-oxo-(E)-2-decenal and (E)-2-decenal might be less effective than their
more volatile, shorter chain homologs, 4-oxo-(E)-2-hexenal and (E)-2-hexenal, and that tridecane might
have a synergistic effect. In arena bioassays, a blend of 4-oxo-(E)-2-hexenal, tridecane, and 4-oxo-(E)-
2-decenal deterred ant attacks (Eliyahu et al. 2012). Another study with compounds from the MTG of
Coridius janus (Hemiptera: Pentatomidae) reported that (E)-2-hexenal and tridecane deterred attacks
by Anoplolepis longipes (Formicidae), a natural enemy of C. janus (Gunawardena and Herath 1991).
Overall, these studies suggested that the shorter chain aldehydes such as (E)-2-hexenal and 4-oxo-(E)-
2-hexenal indeed were more effective against predators than their longer chain homologs, and that tri-
decane had an important role in enhancing the efficacy of these aldehydes (Gunawardena and Herath
1991, Eliyahu et al. 2012).
The aldehydes produced by pentatomid bugs provide protection against at least some entomopatho-
genic fungi. Borges et al. (1993) showed inhibition of the entomopathogen Metarhizium anisopliae
(Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae) by two aldehyde allomones, (E)-2-decenal and
(E)-2-hexenal, produced by Nezara viridula. They reported that solutions containing the aldehydes and
tested individually had the same effect when they were combined, and (E)-2-decenal (25 μg) alone
was able to completely inhibit fungal germination. Sosa-Gomez (1997) also showed that (E)-2-decenal
was strongly fungistatic on N. viridula cuticle against M. anisopliae but not against Beauveria and
Paecilomyces spp. Da Silva et al. (2015) found that extracts of MTGs and DAGs, respectively, of adult
and nymphal Tibraca limbativentris, and synthetic versions of the major components, (E)-2-hexenal,
(E)-2-octenal, and (E)-2-decenal, inhibited spore germination, growth, and sporulation of M. anisopliae
strain CG168, which is expected to be registered for commercial use against this pentatomid in Brazil.
The decreased susceptibility of later instars and adults to this fungal infection was attributed at least in
part to the greater quantities of the three aldehydes present in these more resistant stages (da Silva et al.
2015). Ulrich et al. (2015) demonstrated the dose-dependent contact and fumigant activity of (E)-2-
hexenal and (E)-2-octenal against M. anisopliae (sensu lato, ARSEF 1548) and a protective effect of
(E)-2-octenal against mortality from M. anisopliae in the bed bug Cimex lectularius L. (Cimicidae).
Preliminary results with Halyomorpha halys suggest that adult bugs in groups are less susceptible
to mortality from M. anisopliae, but the mechanisms for this apparent effect are still being pursued
(R. St. Leger, pers. comm.).
15.3.3 Other Behavioral Roles: Within Species
Volatile aldehydes and esters are primarily responsible for the strong odor that stink bugs emit when
stressed, and in addition to deterring predation, these and other gland components also may have intra-
specific roles in communication. Also, different effects can be elicited by different doses: in low quan-
tities, compounds can act as aggregation pheromones, and, in larger quantities, as alarm pheromones
(Ishiwatari 1976). Similarly, Lockwood and Story (1985) reported that tridecane acts as an aggregation
pheromone at low doses and as an alarm pheromone at high doses in Nezara viridula. However, given
more recent studies indicating that the aggregation pheromone of N. viridula consists of bisabolene
epoxides (vide supra), this earlier report must be treated with caution. Furthermore, there also are con-
tradictory reports on the biological roles of hydrocarbons normally present in stink bug secretions. For
example, Fucarino et al. (2004) were not able to reproduce the results of Lockwood and Story (1987),
likely because the doses used in the Lockwood and Story study were well above the biologically relevant