Halyomorpha halys (Stål) 261
Because the northern slopes of mountains receive less solar radiation and stronger winds, adults tend to
gather on the sunnier southern slopes with sedimentary rock outcroppings prior to entering overwinter-
ing sites (Wang and Wang 1988).
4.4.8 Potential Geographic Distribution of Halyomorpha halys:
Ecological Niche Modeling
Biological invasion represents a major threat to biodiversity and ecosystem functioning, resulting in great
economic losses. To mitigate the often dramatic consequences, a fundamental goal in conservation biol-
ogy is to predict which species will invade, as well as which areas are most vulnerable to their invasion.
Recently, considerable progress has been made in identifying regions at risk of species invasion and
understanding the multiple factors that influence the spread of invasive species at local and global scales.
Predicting species’ distributions using an ecological niche modeling (ENM) approach has emerged as
a powerful tool in studying biological invasions (Zhu et al. 2012). The general idea behind correlative
ENMs is to compute a model of a species’ realized niche based on information on the species’ occur-
rence and environmental data commonly stored as geographic information system (GIS) layers. The
output is a map showing relative suitability of each grid cell for the species, which can be used to identify
and prioritize sites for protection against invasion.
The classic applications of ENM to biological invasions involve the calibration of niche modeling in
the native range and the subsequent transfer of the calibrated models to other regions to predict areas of
potential invasion. Based only on niche conservatism, the calibrated model can be projected to identify
areas of potential invasion. Halyomorpha halys, native to east Asia, has become an invasive species in
the United States and Europe. In east Asia, the species spans from temperate to subtropical zones, feed-
ing on a wide variety of fruit and ornamental trees. In the United States, this bug was imported acciden-
tally in the late 1990s and now is emerging as a key pest in agriculture, creating major nuisance problems
especially in the mid-Atlantic region. In Europe, it first was discovered in Switzerland in 2008 and later
was found in Liechtenstein, Germany, and France. The northern China populations have proven to be the
original sources of this bug’s invasion in the United States (Xu et al. 2014) and likely also is the source
of the European invasion in Switzerland.
Climate spaces occupied by the geographic separated population were compared in the ecological
dimensions. The introduced occurrence clusters fell well into that of the native occurrence. This sug-
gests that the climate niche was conserved during the invasion of Halyomorpha halys (Zhu et al. 2012)
(Figure 4.4) providing the fundamental support of using ENM to predict the potential establishment of
3
Native
Invasive – USA(^2) Invasive – Europe
1
0
-1
-2
-3
-4
-3 -2 -1 01
PC-1 (38.4%)
PC
-2 (23.8%)
234
FIGURE 4.4 (See color insert.) Principal component analysis of 10 variables associated with occurrences of
Halyomorpha halys. Symbols represent occurrences of the bug in native areas in Asia and introduced areas in the United
States and Europe (modified from Figure 2 in Zhu et al. 2012).