Halyomorpha halys (Stål) 273
similar to the true pheromone in structure to trigger behavioral responses. Importantly, mixtures of
stereoisomers containing pheromone components are highly attractive to this bug even in the presence
of multiple “unnatural” stereoisomers, indicating that attraction to pheromonal and non-pheromonal
stereoisomers and a lack of inhibition from non-pheromonal stereoisomers increases the flexibility of
developing pheromone-based products for H. halys (Leskey et al. 2015b). The use of plant volatiles to
enhance pheromone attraction also has been examined. Morrison et al. (2017b) determined that plant
volatile extract mixtures derived from either apple, peach or a green leaf volatile mixture combined with
pheromone caused a small increase in H. halys retention on plants, and that plant species could modu-
late H. halys’ retention. However, the addition of plant volatiles did not increase H. halys attractiveness
to baited pyramid traps. For a complete review of H. halys’ chemical ecology, see Weber et al. (2017).
Ultimately, it is hoped that biological information from captures generated from baited pyramid traps
can be used as decision-based support tools (i.e. thresholds) for growers. The first of these tools has been
developed for apples. Short et al. (2016) showed that with the use of baited pyramid traps, a cumulative
threshold of 20 adults per trap resulted in significantly higher damage levels when compared to cumula-
tive thresholds of 1 or 10 adults per trap. They also demonstrated that a cumulative threshold of 10 adults
per trap reduced insecticide applications by 40%.
Trunk traps have been developed to examine the movement of Halyomorpha halys nymphs up and
down host trees by comparing the use of modified ‘Circle’, ‘Hanula’, and ‘M&M’ traps in the laboratory
and in the field (Acebes-Doria et al. 2015). In the laboratory using nymphs released at the top and bottom
of Tree of Heaven, Ailanthus altissima, logs, Circle and M&M traps caught significantly more nymphs
moving up the logs. These two traps also caught the highest number of nymphs moving up and down
A. altissima trees in the field.
Finally, real-time presence of populations of Halyomorpha halys in crops has been conducted using
timed visual counts. Timed counts have been conducted in peaches (Blaauw et al. 2014) and apples
(Leskey et al. 2012c), although no thresholds exist at present for triggering management decisions in
peaches. Timed visual counts also have been used in row crops and have revealed that monitoring efforts
should be focused on crops bordering wooded habitats, as these are the adjacent habitats most likely
to yield significant populations of this bug infesting nearby crops (Venugopal et al. 2014, Aigner et al.
2017). Other methods have included sweep nets (Nielsen et al. 2011, Leskey et al. 2012c, Aigner et al.
2017) and beat samples (Nielsen and Hamilton 2009a,b) to document this bug’s presence in various host
plants and cropping systems, although they are not recommended currently to monitor its populations in
most crops with the exception of soybean.
4.6.2 Biofix Models
A biofix is a biological occurrence or indicator of a particular aspect of a pest insect’s development
that initiates the calculation of growing-degree-days in order to time a management tactic (Anonymous
2015a). To use a biofix event in management models, the development of an insect pest must be char-
acterized. Developmental rates and life table analyses for Halyomorpha halys in North America has
shown that females require ≈148 DD 25 to complete the preoviposition period and ≈538 DD 14 to complete
development from egg to adult (Nielsen et al. 2008a) with similar results reported for European popula-
tions (Haye et al. 2014b). Application of the DD requirements has been used in New Jersey to predict
the peak flight period of the F1 adults as they eclose and presumably search for mates or other resources
(Nielsen et al. 2013). However, there are still some misalignments in the phenology model. Nielsen et
al. (2016a) addressed this through the development of an agent-based stochastic model, using tempera-
ture and photoperiod, that accurately predicts population growth and voltinism at several locations in
the United States. Currently, refinements to the preoviposition period as well as the appropriate biofix
threshold currently are being made by Anne L. Nielsen (unpublished data). Management programs for
H. halys in peach orchards have used a biofix of 148 DD accumulation (or “accumulating” as written
before) beginning on 1 January for initiating insecticidal sprays aimed at adult populations (Anne L.
Nielsen, unpublished data; Blaauw et al. 2014) with good success. Further refinements of the model are
underway and applications to other cropping systems are being pursued.