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. aphidimyza over the full 168 h.
During its 3 h tenure, H. axyridis also acted as a significant intraguild predator of
A. aphidimyza.
This IGP did not result in a release of aphid populations from overall control; aphid population sexposed to both predators were not significantly different 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 result in a release of aphid
population from control as A. aphidimyza is simply not eficient enough at the densities tested to suppress the aphid on its own.
A somewhat different picture emerges for the C. carnea and H. axyridis interaction.
As in the previous experiment,H. axyridis alone slowed but did not prevent the eventual
increase of A. glycines to high levels. However, in contrast to A. aphidimyza, C. carnea larvae alone were able to maintain
A. glycines
populations at low levels throughout the
experiment. IGP of an e
V
ective predator could potentially
release aphids from control. While
H. axyridis
did signi
W
-
cantly reduce
C. carnea
, it did not reduce the levels of this
intraguild prey to the same degree as it did
A. aphidimyza
.
This may be because
C. carnea
are larger, more mobile, or
less preferred intraguild prey than
A. aphidimyza
. The over-
all result was that either
C. carnea
alone or the combination
of
C. carnea
and
H. axyridis
together resulted in experi-
ment-long aphid control.