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feeding bouts within an aphid colony, removing some of the aphid population before moving on to feed elsewhere (Landis unpublished data).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 fields.
Our hypothesis was that during this early season time period H. axyridis adults may release soybean aphid populations from overall control by acting as intraguild predators 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 fields spend their entire juvenile stage feeding primarily on the soybean aphid on a single plant or foraging among a few plants within a field.
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 effect on A. glycines populations.
The objectives of this study were to: (1) investigate how the presence of H. axyridis impacts populations of the native predators A. aphidimyza and C. carnea in soybean agroecosystems and (2) determine if IGP among these arthropods impacts soybean aphid population dynamics.