1.2. Impact of IGP on early season biological control
A critical time in the biological control of soybean aphid occurs in the early season when aphids begin to colonize soybean plants.
We have observed that when aphid populations are low and patchy, adult H. axyridis act as “transient predators,” spending short feeding bouts within an aphid colony, removing some of the aphid population before moving on to feed elsewhere (Landis unpublished data).
Through a review of mark-recapture studies this behavior was also described by
Evans (2003) who stated that coccinellids often do not remain long in any one location and will forage in many different habitats throughout their breeding season.
When aphid populations are low, adult coccinellids are less likely to lay eggs (Evans, 2003); therefore lady beetle larvae are not yet abundantly present in soybean
W
elds.
Our hypothesis was that during this early season time
period
H. axyridis
adults may release soybean aphid popu-
lations from overall control by acting as intraguild preda-
tors of smaller “resident predators”, including larvae of the
aphid predatory midge
A. aphidimyza
and green lacewing
C. carnea
. As immature stages these species have limited
mobility; individuals in soybean
W
elds spend their entire
juvenile stage feeding primarily on the soybean aphid on a
single plant or foraging among a few plants within a
W
eld. If
H. axyridis
acts as an intraguild predator and removes the
majority of these small resident predaceous larvae, the
remaining aphids could be released from overall control.
However, if
H. axyridis
feeds primarily on aphids, these
species may have an additive negative e
V
ect on
A. glycines
populations. The objectives of this study were to: (1) inves-
tigate how the presence of
H. axyridis
impacts populations
of the native predators
A. aphidimyza
and
C. carnea
in soy-
bean agroecosystems and (2) determine if IGP among these
arthropods impacts soybean aphid population dynamics.