Predators Exert Top-Down Control of Soybean Aphid Across a Gradient of Agricultural Management Systems

Abstract

The discovery of soybean aphid, Aphis glycines Matusumura, in North America in 2000 provided the opportunity to investigate the relative strength of top-down and bottom-up forces in regulating populations of this new invasive herbivore. At the Kellogg Biological Station Long Term Ecological Research site in agroecology, we contrasted A. glycines establishment and population growth under three agricultural production systems that differed markedly in disturbance and fertility regimes. Agricultural treatments consisted of a conventional-tillage high-input system, a no-tillage high-input system, and a zero-chemical-input system under conventional tillage. By selectively restricting or allowing predator access we simultaneously determined aphid response to top-down and bottom-up influences. Irrespective of predator exclusion, our agricultural manipulations did not result in bottom-up control of A. glycines intrinsic rate of increase or realized population growth. In contrast, we observed strong evidence for top-down control of A. glycines establishment and overall population growth in all production systems. Abundant predators, including Harmonia axyridis, Coccinella septempunctata, Orius insidiosus, and various predaceous fly larvae, significantly reduced A. glycines establishment and population increase in all trials. In contrast to other systems in which bottom-up forces control herbivore populations, we conclude that A. glycines is primarily controlled via top-down influences of generalist predators under a wide range of agricultural management systems. Understanding the role of top-down and bottom-up forces in this context allows agricultural managers to focus on effective strategies for control of this invasive pest.

What Is the Economic Threshold of Soybean Aphids (Hemiptera: Aphididae) in Enemy-Free Space?

“…Previous studies have shown natural enemies to have a large impact on the regulation of soybean aphid populations , Costamagna and Landis 2006, Schmidt et al 2007, Gardiner et al 2009b. In all cases, these studies focused on the growth of initial populations of aphids at low densities (1Ð10 aphids per plant).…”

“…Despite the large body of literature that indicates natural enemies regulate soybean aphid populations (Fox et al , 2005Rutledge et al 2004;Nielsen and Hajek 2005;OÕNeil 2005, Costamagna andLandis 2006;Schmidt et al 2007Schmidt et al , 2008, economic outbreaks are common in North America. Why these outbreaks occur is unclear, although several factors can contribute to increasing the risk for soybean aphid outbreaks.…”

Intersection between biodiversity conservation, agroecology, and ecosystem services

“…The presence of decomposing organic matter at the soil surface, characteristic of no-till systems, provides predators with alternative prey when crop pests are scarce thus maintaining predator populations in fallow periods or in annual cropping systems (Landis, Wratten, and Gurr 2000;Sigsgaard 2000). Yet, some predator groups, such as carabid (Hatten et al 2007) and coccinellid beetles (Costamagna and Landis 2006), demonstrate more idiosyncratic responses. Likewise, some soil practices that increase the area of bare ground and increase loosening of compacted soils (RogerEstrade et al 2010) can have positive effects on ground-nesting bees (Julier and Roulston 2009).…”

Biotic and Abiotic Influences on Within-Plant Distribution of Soybean Aphid (Hemiptera: Aphididae: Aphis glycines)

“…Natural enemies are capable of suppressing soybean aphid populations (Fox et al, 2004;Costamagna and Landis, 2006;Desneux et al, 2006;Brosius et al, 2007). The presence of natural enemies influences the withinplant distribution of many aphid species (Roitberg et al, 1979;Gonzales et al, 2001), and potentially soybean aphid (Rutledge and O'Neil, 2005).…”