Spatial niche selection indices for <i>D</i>. <i>citri</i> adults in three habitat types in commercial citrus groves in South Texas (2009–2012).

<p>¹<i>W</i>_i = selection index of <i>D</i>. <i>citri</i>; Selection indices followed by the same letter are not significantly different at P = 0.05 (log-likelihood ratio [G] test).</p><p>²<i>B</i>_<i>i</i> = standardized selection index for <i>D</i>. <i>citri</i>; standardized selection indices of (1/number of habitats), or 0.33 in this case, indicate no preference. Values above 0.33 indicate relative preference, and values below 0.33 indicate relative avoidance.</p><p>Habitat types are represented by perimeter, adjacent and interior trees.</p

Mixed model analysis of variance showing <i>F</i>-values¹ of major parameters affecting <i>D</i>. <i>citri</i> densities and infestation levels in mature citrus groves in Texas (2009–2010).

<p>Error df for all analysis = 35,000.</p><p>¹ ns = non-significant (P>0.05).</p><p>** = highly significant (P < 0.01).</p><p>Mixed model analysis of variance showing <i>F</i>-values<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131917#t001fn002" target="_blank">¹</a> of major parameters affecting <i>D</i>. <i>citri</i> densities and infestation levels in mature citrus groves in Texas (2009–2010).</p

Contour maps of <i>D</i>. <i>citri</i> adults caught on ACP-traps deployed at different positions in young and mature grapefruit groves in a field study (TAMUK-Citrus Center, 2012).

<p>Contour maps of <i>D</i>. <i>citri</i> adults caught on ACP-traps deployed at different positions in young and mature grapefruit groves in a field study (TAMUK-Citrus Center, 2012).</p

Exponential decay function (<i>y</i> = <i>a</i>*<i>exp</i> [<i>-bx</i>]) describing the decrease in <i>D</i>. <i>citri</i> densities and infestation levels from the edge to the interior of the grove in area-wide surveys.

<p>Exponential decay function (<i>y</i> = <i>a</i>*<i>exp</i> [<i>-bx</i>]) describing the decrease in <i>D</i>. <i>citri</i> densities and infestation levels from the edge to the interior of the grove in area-wide surveys.</p

Living on the Edges: Spatial Niche Occupation of Asian Citrus Psyllid, <i>Diaphorina citri</i> Kuwayama (Hemiptera: Liviidae), in Citrus Groves

<div><p>The spatial niche occupation of the Asian citrus psyllid, <i>Diaphorina citri</i> Kuwayama, 1908, was evaluated to determine its field colonization and food resource exploitation strategies in citrus groves. Mature grapefruit and sweet orange groves were surveyed as part of an area-wide program in 2009–2010 to determine <i>D</i>. <i>citri</i> population densities and between-tree distribution. In both cultivars, significantly more psyllids were found on perimeter trees throughout the study period suggesting a strong edge effect in <i>D</i>. <i>citri</i> distribution in the groves. <i>D</i>. <i>citri</i> densities and infestation levels gradually declined from the edge to the center of grove. Higher numbers of <i>D</i>. <i>citri</i> were recorded on trees located on the east and south sides of the groves than those on the west and north sides. Citrus groves located at the outer edge of the study with at least one side non-surrounded to other citrus groves harbored significantly more <i>D</i>. <i>citri</i> than groves located within the block cluster and entirely surrounded by other groves. In detailed field studies during 2012, infestation of <i>D</i>. <i>citri</i> started from border trees in the grove where possibly one generation is completed before inner trees become infested. In addition, psyllid densities decreased significantly with increasing distance from the grove edge. Using the selection index, <i>D citri</i> exhibited a strong niche occupation preference for border trees.</p></div

Cluster heatmap describing the relative concentrations of free amino acids in phloem sap of permissive hosts of <i>Candidatus</i> Liberibacter asiaticus, non-permissive plants and whole <i>Diaphorina citri</i> nymphs and adults (OJY = young orange jasmine, OJM = mature orange jasmine, CLY = young curry leaf, CLM = mature curry leaf, WSY = young white sapote, WSM = mature white sapote, GFY = young grapefruit, GFM = mature grapefruit, SOY = young sweet orange, SOM = mature sweet orange, LEY = young lemon, LEM = mature lemon, PW = periwinkle plant, ACPAd = <i>D</i>. <i>citri</i> adults, and ACPNy = <i>D</i>. <i>citri</i> nymphs).

<p>Cluster heatmap describing the relative concentrations of free amino acids in phloem sap of permissive hosts of <i>Candidatus</i> Liberibacter asiaticus, non-permissive plants and whole <i>Diaphorina citri</i> nymphs and adults (OJY = young orange jasmine, OJM = mature orange jasmine, CLY = young curry leaf, CLM = mature curry leaf, WSY = young white sapote, WSM = mature white sapote, GFY = young grapefruit, GFM = mature grapefruit, SOY = young sweet orange, SOM = mature sweet orange, LEY = young lemon, LEM = mature lemon, PW = periwinkle plant, ACPAd = <i>D</i>. <i>citri</i> adults, and ACPNy = <i>D</i>. <i>citri</i> nymphs).</p

Correlation between mean amino acid concentrations and <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las) permissivity status of different plants and <i>Diaphorina citri</i> (ACP) adults and nymphs.

<p>Correlation between mean amino acid concentrations and <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las) permissivity status of different plants and <i>Diaphorina citri</i> (ACP) adults and nymphs.</p