4.1. Microcosm studies
In microcosm experiments we found that H. axyridis acting as both an intraguild and a direct predator had differential impacts on both the survival of the intraguild
prey and A. glycines population dynamics.
In tests with A. aphidimyza, the presence of this predator alone slowed,but did not prevent, the eventual increase of A. glycines to high levels. Based on this result and the aphid consumption rate data we conclude that under the conditions tested, A. aphidimyza was not eficient enough in preventing the
aphid from reaching outbreak levels. In contrast, only 3 h of
feeding by
H. axyridis
provided suppression of
A. glycines
essentially equal to the continuous presence of
A. aph-
idimyza
over the full 168 h. During its 3 h tenure,
H. axyri-
dis
also acted as a signi
W
cant intraguild predator of
A. aphidimyza
. This IGP did not result in a release of aphid
populations from overall control; aphid populations
exposed to both predators were not signi
W
cantly di
V
erent
from aphids exposed only to
A. aphidimyza
. The overall
picture that emerges from this experiment is that while
H. axyridis
is an intraguild predator of
A. aphidimyza
, IGP
did not release
A. glycines
from control as
A. aphidimyza
is
simply not e
Y
cient enough at the densities tested to
suppress the aphid on its own.