Top-down and bottom-up effects on aphid population growth rates.

<p>We present means (+1 SE) of <i>A. glycines</i> intrinsic rate of increase (aphids×aphids⁻¹×day⁻¹) for trials 1 (A), 2 (B), and 3 (C)<b>.</b> See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056394#pone-0056394-g003" target="_blank">Figure 3</a> for other references.</p

Top-down and bottom-up effects on aphid within-plant distribution.

<p>Top-down controls were manipulated as upper predation (ambient levels = +UP, or exclusion = −UP), and lower predation (ambient levels = +LP, or exclusion = −LP) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056394#pone-0056394-g001" target="_blank">Figure 1</a> for cage designs); bottom-up controls were manipulated using plants of different age (old = O, grey bars; or young = Y, white bars, plants). We present means (+1 SE) of the proportion of <i>A. glycines</i> on the upper nodes of the plants for trials 1 (A), 2 (B), and 3 (C). Means that do not share letters are significantly different (<i>P</i><0.05, LSMD-TK tests). The dashed line indicates equal proportion at the upper and lower nodes of the plant, and asterisks above and below the line indicate significant departure from equality, testing the alternative hypothesis of different than 0.5 (controls −LP−UP, and +LP+UP), smaller than 0.5 (−LP+UP) or greater than 0.5 (+LP−UP), using <i>t</i>-tests (<i>P</i><0.05). Small graphs (ii – iv) at the right of the main graphs (i) indicate main effects; asterisks indicate significant differences (<i>P</i><0.05, ANOVA main effect tests, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056394#pone-0056394-t001" target="_blank"><b>Table 1</b></a>).</p

Bottom-up effects of within-plant quality on <i>A. glycines</i> population growth rates under predator exclusion.

<p>(A)–(C) present results for trials 1–3, respectively. Old versus young plants were compared in trials 1 and 2, and only old plants were available for trial 3. Upper nodes represent the 3–4 top nodes (∼ 10% of the plant canopy) and lower nodes represent the rest of the plant nodes. All graphs show means (+1 SE) of <i>A. glycines</i> intrinsic rate of increase (aphids×aphid⁻¹×day⁻¹); asterisks indicate significant differences between plant parts within old or young plants (<i>t</i>-test, <i>P</i><0.05).</p

Cages used for the four manipulations of predator access to aphids at the within-plant scale.

<p>Predator treatments (LP = lower predation, UP = upper predation) corresponded to (A) predator exclusion (−LP−UP), (B) lower predation (+LP−UP), (C) upper predation (−LP+UP), and (D) ambient levels of predation (+LP+UP). The small grid pattern represents the mesh covers used to prevent aphid and natural enemy movements.</p

Effects of plant age (PA) on naturally occurring populations of <i>A. glycines</i> and predators in the experimental plots.

<p>Bars present mean (+1 SE) of (A) log₁₀– transformed number of aphids/plant, from a sample of 10 random plants per plot in each date, and (B) total number or predators/25 sweeps, from four samples/plot. PA 1–3 refers to the oldest to the youngest plant age, respectively. Horizontal lines indicate the dates when the manipulative trials were conducted.</p

Top-down impacts on <i>A. glycines</i> dispersal among soybean plants. (

<p>A) Number, and (B) proportion of aphids settled after five days of exposure to predation (four days for sham cages, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056394#s2" target="_blank">materials and methods</a> for more details). Fifty aphids were released in the central 5 plants (release plants) and exposed to three treatments: lady beetles, sham and control. Lady beetle cages received five adults (<i>H. axyridis</i> and <i>C. septempunctata</i> combined) per cage, sham cages were exposed to ambient levels of all predators present in the field, and control cages had aphids only. Different letters indicate significant differences (<i>P</i><0.05, Tukey HSD tests); NS = not significant differences (<i>P</i>>0.05, one-way ANOVAs).</p