Agriculture Reference
In-Depth Information
(Gardiner et al. 2009a). An analysis of the value of biodiversity for aphid protec-
tion in these landscapes showed that for soybean producers using an integrated
pest management strategy, natural suppression of aphids was worth ~$33 ha
−1
in
increased yield and decreased pesticide use in 2007, summing to >$239 million yr
−1
for the four midwestern states studied (Landis et al. 2008).
KBS LTER research on soybean aphid-natural enemy interactions has yielded
a number of key insights. First, results of observations and experiments support
the hypothesis that communities of generalist natural enemies can provide effec-
tive herbivore suppression. At present, parasitoids are minor contributors to sup-
pression in the soybean-aphid system, but could become more important with the
importation of more effective parasitoid species (Wyckhuys et al. 2009), although
intraguild predation could limit their effectiveness (Chacon et al. 2008). Second,
soybean aphids serve as a food source and when abundant can support high coc-
cinellid populations, particularly
H. axyridis
. This species, in turn, can act as an
intraguild competitor, increasing its potential for negative impacts on native coc-
cinellids (Colunga-Garcia and Gage 1998, Gardiner et al. 2011). Finally, based
in part on data from KBS LTER, the soybean aphid system has been proposed
as an example of “invasional meltdown” (
sensu
Ricciardi and MacIsaac 2000,
Simberloff 2006), where the prior establishment of one exotic paves the way for
others. Indeed, researchers investigating the soybean-soybean aphid system have
documented such a cascade involving interactions among 11 Eurasian species
(Heimpel et al. 2010).
Summary
Twenty years of arthropod studies at KBS LTER have yielded insights that both
confirm and extend ideas about basic ecology and the ecosystem services and
disservices that arthropods contribute to agroecosystems. In particular, studies
of arthropods at KBS have yielded insights relevant to basic population biol-
ogy, food web ecology, and invasion biology theory. Studies of the soybean
aphid have contributed to our understanding of top-down vs. bottom-up forces
(Costamagna and Landis 2006); intraguild predation (Costamagna and Landis
2007, Gardiner and Landis 2007, Costamagna et al. 2008); trophic cascades in
food webs (Costamagna et al. 2007a); and landscape control on herbivore-natu-
ral enemy interactions (Landis et al. 2008; Gardiner et al. 2009a, b). Population
modelers have also used the soybean aphid system to elucidate a novel formu-
lation of exponential growth based on cumulative density-dependent feedback
(Costamagna et al. 2007, Matis et al. 2009). Moreover, they suggest key ways in
which such systems may be designed to enhance desirable ecosystem services in
the future.
One of the earliest and perhaps most fundamental lessons learned is that crop-
ping systems form the proximate template on which pest and natural enemy
interactions play out. The distribution of carabid beetles is sensitive to soil dis-
turbance (e.g., till vs. no-till) and crop persistence (e.g., annual vs. perennial),
