Alfalfa Living Mulch Advances Biological Control of Soybean Aphid

Abstract

Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycinesestablishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate ofA. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids' intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction. RightsThis article is the copyright property of the Entomological Society of America and may not be used for any commercial or other private purpose without specific written permission of the Entomological Society of America.This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ent_pubs/11BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Alfalfa Living Mulch Advances Biological Control of Soybean AphidAuthor (s) ABSTRACT Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-Þeld habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medica...

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“…botrytis) monoculture when compared to broccoli with undersown mulches like strawberry clover (Tribolium fragiferum L.), white clover (Tribolium repens L.), and yellow sweet clover (Melilotus officinalis L.) (Hooks & Johnson 2004). Alfalfa living mulch increased predators to manage outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Schmidt et al 2007).…”

“…Different types of cover crops harbor distinctive complexes of beneficial insects, pest arthropods, and their diverse trophic relationships (Bugg & Waddington 1994). Many previous studies that used mulches for the management of insect pests focused especially on flying insects moving into mulched areas (Brown & Tworkoski 2004;Gill et al 2010;Hooks & Johnson 2004;Prasifka et al 2006;Pullaro et al 2006;Reeleder et al 2004;Schmidt et al 2007;Tremelling et al 2002). The effects of mulches on insects and other soil arthropods living on the soil surface is a relatively less explored area.…”

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.…”

“…Previous studies have used cages to estimate the impact of predators on soybean aphid populations , Schmidt et al 2007, Gardiner et al 2009b. By comparing the growth of aphid populations within cages to those outside cages, several studies have observed a substantial decrease in aphid population growth when predators have access to aphids.…”