Relationship of Soybean Aphid (Hemiptera: Aphididae) to Soybean Plant Nutrients, Landscape Structure, and Natural Enemies

Abstract

Abstractn the north central United States, populations of the exotic soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), are highly variable across space, complicating effective aphid management. In this study we examined relationships of plant nutrients, landscape structure, and natural enemies with soybean aphid abundance across Iowa, Michigan, Minnesota, and Wisconsin, representing the range of conditions where soybean aphid outbreaks have occurred since its introduction. We sampled soybean aphid and its natural enemies, quantified vegetation land cover and measured soybean nutrients (potassium [K] and nitrogen [N]) in 26 soybean sites in 2005 and 2006. Multiple regression models found that aphid abundance was negatively associated with leaf K content in 2005, whereas it was negatively associated with habitat diversity (Simpson's index) and positively associated with leaf N content in 2006. These variables accounted for 25 and 27% of aphid variability in 2005 and 2006, respectively, suggesting that other sources of variability are also important. In addition, K content of soybean plants decreased with increasing prevalence of cornsoybean cropland in 2005, suggesting that landscapes that have a high intensification of agriculture (as indexed by increasing corn and soybean) are more likely to have higher aphid numbers. Soybean aphid natural enemies, 26 species of predators and parasitoids, was positively related to aphid abundance; however, enemyto-aphid abundance ratios were inversely related to aphid density, suggesting that soybean aphids are able to escape control by resident natural enemies. Overall, soybean aphid abundance was most associated with soybean leaf chemistry and landscape heterogeneity. Agronomic options that can ameliorate K deficiency and maintaining heterogeneity in the landscape may reduce aphid risk. KeywordsAphis glycines, biological control, landscape ecology, plant chemistry, potassium Disciplines Agriculture | Entomology CommentsThis article is from Environmental Entomology 39 (1) Soybean aphid natural enemies, 26 species of predators and parasitoids, was positively related to aphid abundance; however, enemy-to-aphid abundance ratios were inversely related to aphid density, suggesting that soybean aphids are able to escape control by resident natural enemies. Overall, soybean aphid abundance was most associated with soybean leaf chemistry and landscape heterogeneity. Agronomic options that can ameliorate K deÞciency and maintaining heterogeneity in the landscape may reduce aphid risk.

Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a holocyclic heteroecious aphid species

“…In Klueken et al (2011), secondary host colonizers from the primary plant source had a R of 0.96, and the earliest aphid populations on the secondary host had a R of 1.0, suggesting high initial genotypic diversity during secondary host colonization. Selection could be in the form of plant quality (Noma et al, 2010), insecticidal seed treatments (Magalhaes et al, 2009), soybean variety or other characteristics related to common agronomic practices.…”

Increased area of a highly suitable host crop increases herbivore pressure in intensified agricultural landscapes

“…Studies examining regional variation in landscape effects on agricultural pests remain uncommon (but see Noma et al, 2010;O'Rourke et al, 2011;Thies et al, 2011). Landscape influences may vary regionally for a number reasons including shifting pest and enemy complexes, shifts in cropping systems or crop composition, or changes in the levels of landscape domination by agriculture across regions Thies et al, 2011).…”

European buckthorn and Asian soybean aphid as components of an extensive invasional meltdown in North America

“…In China and the Eastern United States, both generalist predators and more specialized parasitoids are important (van den Berg et al 1997;Liu et al 2004;Wu et al 2004b;Miao et al 2007;Nielsen and Hajek 2005;Hajek et al 2007;Wu, Heimpel and Hopper, unpublished data;see below). In the NorthCentral US, however, parasitoids have little impact on A. glycines (Lin and Ives 2003;Rutledge et al 2004;Costamagna and Landis 2006;Kaiser et al 2007;Noma and Brewer 2008;Noma et al 2010) and at least one predator that is present in Eastern N. America (A. muelleri) is absent from soybean fields (see below). In Asia, parasitism rates ranging between 45 and 52% were routinely recorded over a 5 year period in Jilin province (Gao 1994), one of the principal soybean producing areas.…”

“…Substantial parasitoid species diversity and parasitism rates have also been found during ongoing exploration for soybean aphid parasitoids in China and Korea, and parasitized aphids were routinely found whenever aphids were located (K Hoelmer, unpublished). Other hypotheses involve differences in climate, agricultural practices or cultivars of soybean, as well as landscape-level habitat differences that could interact with natural enemy impact (Gardiner et al 2009a, b;Noma et al 2010). Critical tests that could be used to test the hypothesis that soybean aphid abundance is linked to local or regional Rhamnus abundance could include landscape-level analyses that seek spatial correlation between buckthorn and soybean aphid outbreaks.…”