Semiochemistry of Pentatomoidea 691
component also attracted nymphs (Khrimian et al. 2014a). Furthermore, lures prepared from mixtures
of stereoisomers also were attractive (Khrimian et al. 2014a, Weber et al. 2014a, Leskey et al. 2015b),
demonstrating that the presence of additional stereoisomers apparently does not hinder attraction of
H. halys. This may make it economically feasible to produce isomer mixtures of aggregation pheromone
for H. halys management. In an effort to simplify large-scale production and reduce the cost of the
H. halys pheromone, Leskey et al. (2015b) reported a synthesis of “technical grade” pheromone from
either (R)- or racemic citronellals using only one distillation and no chromatography throughout the
whole synthesis. The resulting mixtures of isomers attracted bugs in field bioassays (Leskey et al. 2015b),
with or without the synergist methyl (2E,4E,6Z)-2,4,6-decatrienoate (vide infra), and were used to moni-
tor populations of H. halys in ten states across the United States (Leskey et al. 2015a). Although system-
atic studies of lure dose and formulations have not yet been conducted, rubber septa impregnated with
10.7 mg of more purified pheromone, or 31 mg of the “technical grade” mixture of eight isomers produced
from the large-scale synthesis from (R)-citronellal (both containing ~2 mg of the most active pheromone
component 37 ) remained attractive for 2–3 weeks in field trials (Leskey et al. 2015a,b). Controlled-release
formulations of H. halys pheromone are currently being developed by several semiochemical companies
(A.K., pers. comm.)
15.2.9.2 Attraction of Halyomorpha halys to the Pheromone of Plautia stali
It was discovered serendipitously that H. halys is attracted to methyl (2E,4E,6Z)-2,4,6-decatrienoate
(Tada et al. 2001a,b; Lee et al. 2002), the aggregation pheromone of the brown-winged green stink bug,
Plautia stali (Sugie et al. 1996), with which it is sympatric in northeast Asia. This cross-attraction was
confirmed in the United States after H. halys became established (Aldrich et al. 2007, Khrimian et al.
2008). Although this compound is somewhat unstable under field conditions, Khrimian et al. (2008)
demonstrated that about 80% of methyl (2E,4E,6Z)-2,4,6-decatrienoate could be preserved on rub-
ber septum dispensers if the dispensers were shielded from direct sunlight (see also section below for
Thyanta perditor). However, field studies showed that preventing isomerization of methyl (2E,4E,6Z)-
2,4,6-decatrienoate was not essential because H. halys adults and nymphs were still attracted to mixtures
of methyl 2,4,6-decatrienoate isomers, indicating that other cis-trans isomers were not antagonistic.
Furthermore, methyl (2Z,4E,6Z)-2,4,6-decatrienoate and methyl (2E,4Z,6Z)-2,4,6-decatrienoate (phero-
mone of pentatomid Thyanta spp.) attracted H. halys, possibly through isomerization to the (2E,4E,6Z)-
isomer. Alternatively, one or more of these other isomers may be attractive in their own right. Until the
actual pheromone was identified, (2E,4E,6Z)-2,4,6-decatrienoate was the primary lure used in traps to
monitor H. halys after it became established in the United States (Leskey et al. 2012b). However, the
lures primarily were attractive in the late season in both Japanese and American studies, limiting their
value for monitoring during a major part of the growing season (Funayama 2008, Leskey et al. 2012b).
Funayama (2008) assessed the nutritional status of captured H. halys and hypothesized that H. halys
might be eavesdropping on P. stali pheromone as an indirect method of host location. Intriguingly, he
found a strong response in early season to methyl (2E,4E,6Z)-2,4,6-decatrienoate only during a year
(2001) of high populations, and scattered early-season response in years of moderate populations (2002
and 2006). Weber et al. (2014a) reported analogous results from field trials conducted in Maryland in
April 2012.
The identification of the pheromone actually produced by H. halys males offered new opportunities for
management of this species. Weber et al. (2014a) found that a combination of a mixed-isomer preparation
of the H. halys pheromone with methyl (2E,4E,6Z)-2,4,6-decatrienoate acted synergistically. In season-
long trials using pyramid traps, lures containing both the H. halys pheromone and the decatrienoate
caught 1.9 to 3.2 times more adults, and 1.4 to 2.5 times more nymphs than would be expected from addi-
tive effects of the compounds deployed individually. The pattern of captures of males and females was
similar. Mixed-isomer lures derived from (R)-citronellal, containing eight stereoisomers of 10,11-epoxy-
1-bisabolen-3-ol, (and including the two pheromone components), were as effective at attracting adults
and nymphs with or without methyl (2E,4E,6Z)-2,4,6-decatrienoate, as were lures loaded only with
pure 37 and 38 in the natural ratio. Captures also increased with dose for the mixed-isomer lures with
and without accompanying methyl (2E,4E,6Z)-2,4,6-decatrienoate (Leskey et al. 2015b). These results