Semiochemistry of Pentatomoidea 711
as to the ratio of their two pheromone components, this ratio was almost constant for any given male in
spite of large variations in overall quantities produced. The only three studies to look closely at phero-
mone production by individuals (Ryan et al. 1995, Miklas et al. 2000, Endo et al. 2012) all demonstrated
substantial variability in both quantities produced and blend ratios, and this pattern likely is widespread
among pentatomids. Moraes et al. (2008c) found that well-fed male E. heros produced all three com-
ponents of the attractant pheromone, but those provided only water or neither food nor water, stopped
production of two of the three components while increasing production of allomonal compounds such as
(E)-2-hexenal. For all of the above reasons, researchers must be cautious in designating any set ratio of
multiple components as “the” pheromone ratio for a particular stink bug species.
The fact that the ratio of components and/or the presence of one or more unnatural isomers in syn-
thetic pheromone blends apparently is not critical to pheromone-induced responses for many stink bugs
is contrary to findings for the pheromone blends of most other insects. This anomaly suggests that there
may be more subtle information encoded in the blends, in addition to the attractant signal, and so more
careful study of the variability in stink bug pheromone blends may prove fruitful. The variation in
semiochemical emissions, and the responses to them, must be considered when optimizing attractants
for monitoring and management purposes. Practical optimization of pheromone synthesis may entail
use of more cost-efficient but non-stereoselective syntheses that produce mixtures of products that differ
from the natural ratio(s). For instance, as described above, the pheromone blend of Halyomorpha halys
was found to be a 3.5:1 mixture of two stereoisomers, (3S,6S,7R,10S)-and (3R,6S,7R,10S)-10,11- epoxy-1-
bisabolen-3-ols (Khrimian et al. 2014a). Making sufficient quantities of these pure isomers for practical
applications would be prohibitively expensive. However, a cost-effective synthesis from racemic citronel-
lal yielded these two isomers in 1:1.5-2.0 ratio (Leskey et al. 2015b) admixed with the other 14 possible
isomers. Remarkably, based on the quantity of the major component, the SSRS isomer, this mixture of
16 isomers of 10,11-epoxy-1-bisabolen-3-ol was as attractive in field tests as the 3.5:1 mixture of the two
pure isomers (Leskey et al. 2015b), illustrating that off-ratios of pheromone components and presence of
unnatural isomers may be unimportant in some cases. In contrast, in tests with the two components of
Murgantia histrionica pheromone, Weber et al. (2014b) found that bugs were most strongly attracted to
lures containing the natural 1.4:1 blend of (3S,6S,7R,10S)- and (3S,6S,7R,10R)-10,11-epoxy-1-bisabolen-3-
ols, with decreased attraction to off-ratio lures, which in turn were superior to either single component.
15.5.1.3 Dose and Release Rates of Stink Bug Semiochemicals
Studies quantifying pheromone release by male pentatomids are much less numerous than those docu-
menting identities of components and their proportions. Studies have demonstrated release rates of active
components in the range of a few nanograms to a few micrograms per day per bug, usually with distinct
diurnal rhythms. Also, when density effects were studied, in at least some species, males were found
to produce less pheromone per bug at higher densities. This may account for some of the variability in
quantities reported within species.
For example, Zahn et al. (2008) found that males of Murgantia histrionica release a blend of
10,11-epoxy-1-bisabolen-3-ols at ≈60 ng/bug/hour during peak release during the early afternoon, for
a daily total of approximately 1 μg. The release rate was attenuated significantly (≈6-fold) when 10 or
more male bugs were held in a 400 ml aeration chamber compared to individual bugs or groups of
five bugs. Borges et al. (2007) found that Piezodorus guildinii males release sesquiphellandrene 63 at
a mean rate of ≈40 ng/bug/day, at a density of 20 bugs within a 1-liter glass vessel, but aerations were
not performed at other densities. Endo et al. (2012) measured the 3-component pheromone emissions
by individual male Piezodorus hybneri each day from 1 to 16 days of age. Emission started 3 to 6 days
after the final molt, and typically peaked at ~1 μg/bug/day on day 11 (Endo et al. 2012), exceeding
the original estimate of ~200ng/bug/day of Leal et al. (1998). Bugs that were solvent extracted had a
mean of ~10 μg/bug of total pheromone constituents (Endo et al. 2007). Ho & Millar (2001a, b) found
that male Chlorochroa spp. (10 to 20 virgin males in 1-liter vessels) emitted means of ~320, ~240, and
~77 ng/bug/day for C. ligata, C. sayi, and C. uhleri respectively, each with an evening peak emission, of
their respective major pheromone components. Male Thyanta perditor bugs emitted about 200 ng/bug/
day of their sex pheromone 73 (Moraes et al. 2005a). Chinavia ubica males emitted a mean of ~3.0 and