Abstract
The soybean aphid,
Aphis glycines
Matsumura, has become a principal arthropod pest of soybean in the U.S. since its
W
rst detection in
2000. This species threatens soybean production through direct feeding damage and virus transmission. A diverse guild of insect
preda-
tors feeds on soybean aphid in Michigan including the exotic coccinellid
Harmonia axyridis
, the native gall midge
Aphidoletes aphidimyza
and the native lacewing
Chrysoperla carnea
. In addition to feeding on
A. glycines
some members of this guild may also engage in intra-
guild predation. These interactions may produce positive, negative, or neutral impacts on
A. glycines
biological control. We explored the
impact of intraguild predation on soybean aphid population dynamics by comparing aphid populations in microcosms with either
A.
aphidimyza
larvae or
C. carnea
larvae alone, with both a
H. axyridis
adult and either
A. aphidimyza
or
C. carnea
larvae, and without pre-
dators. When
H. axyridis
was present with larval
A. aphidimyza
or
C. carnea
, the lady beetle acted as an intraguild predator. However,
intraguild feeding did not result in a release of aphid populations compared with microcosms containing only the intraguild and
aphid
prey. A similar result was found in
W
eld cages. Cages allowing large predators had reduced numbers of
A. aphidimyza
and
C. carnea
larvae
but also signi
W
cantly fewer aphids compared with predator exclusion cages. Thus, in both lab and
W
eld studies the direct impact of
H.
axyridis
on
A. glycines
overcame its negative impact as an intraguild predator. Together, these studies indicate that while the exotic
H.
axyridis
does act as an intraguild predator and may contribute to local declines in
A. aphidimyza
and
C. carnea
, it is also currently impor-
tant in overall biological control of
A. glycines
.
©
2006 Elsevier Inc. All rights reserved.