Agriculture Reference
In-Depth Information
Soybean
aphid
studies
2001-2007
Coccinellid
sampling
initiated
Carabid
sampling
1994-1995
Seed
predation
study
1990
1995
2000
2005
C. septempunctata
introduced in Michigan
1985, already present
at KBS in 1988
H. axyridis
detected
A. glycines
detected
H. variegata
detected
P. quatuordecimpunctata
detected
Figure 8.5
. Time line showing insect sampling efforts (above line) and the arrival of key
exotic coccinellid species (below line) to KBS LTER study sites. See Table 8.2 for full names
of coccinellids
; A. glycines
is the soybean aphid
Aphis glycines
.
continued to increase and as early as 2008 was found to be the second most abun-
dant coccinellid in corn after
C. maculata
(Gardiner et al. 2010).
Key lessons of these long-term coccinellid observations include a clearer
understanding of the innate habitat preferences of different species (Fig. 8.3) and
the seasonal movement of coccinellids from noncrop to crop habitats. As these
predators move through the landscape (Isard and Gage 2001), they are influenced
by the availability of prey and, as discussed below, can be important regulators of
prey density. The addition of new exotic coccinellid species into the KBS land-
scape has shaped—and continues to shape—the structure and diversity of these
communities (Bahlai et al. 2013, 2014).
Soybean Aphid: A New Herbivore Changes Everything
The arrival of the soybean aphid
A. glycines
, an exotic invasive herbivore, into
the KBS landscape created an opportunity to evaluate how a new link in the exist-
ing food web alters system dynamics.
A. glycines
is an invasive insect pest from
Asia that was first discovered in the United States in 2000 and rapidly became
the nation's most significant threat to soybean production (Ragsdale et al. 2004).
Prior to its arrival, soybean experienced relatively low insect herbivore pressure and
was seldom treated with insecticides. The arrival of the soybean aphid fundamen-
tally changed soybean production, with the aphid becoming a key pest, frequently
requiring insecticide applications to control (Ragsdale et al. 2011).
The soybean aphid overwinters as an egg on several species of shrubs/small trees
in the genus
Rhamnus
, principally common buckthorn (
R. cathartica
L.), which is
itself an exotic invasive pest. Several generations of
A. glycines
occur on buckthorn
in the spring before alates (winged, sexually mature individuals) are produced and
migrate to soybean. On soybean plants, females reproduce asexually (partheno-
genesis) and give birth to live young, with multiple generations occurring on a
single soybean plant. Soybean aphid populations can reach 30,000 aphids per plant
(DiFonzo 2006, as cited in Walter and DiFonzo 2007) and result in yield losses of
