The isotopic discrimination factors between the tissues of caterpillars (plus ‘+’ signs, dotted line) and moths (open circles, barred line) decreased significantly with the δD value of plant tissues according to a shallow common slope.

<p>Note that the discrimination factors for plants, caterpillars and moths differed significantly from one another (Tukey's test, p<0.05). The horizontal reference line represents ΔD = 0.</p

δD of organic matter and extracted water of plant and insect tissues are linearly correlated to δD of irrigation water.

<p>(a) The δD values of the organic matter of plants (solid triangles, dotted line), caterpillars (plus ‘+’ signs, barred-dotted line), and moths (open circles, barred line) increased linearly with the δD value of irrigation water (y_plant = 0.59x−107.5, r² = 0.74; y_caterpillar = 0.59x−81.2, r² = 0.90; y_moth = 0.59x−67.8, r² = 0.90). These relationships had a common slope that was significantly less than 1. Note that the δD value of soil (open squares) did not differ from that of irrigation water (y = x, solid line). Plant, caterpillar, and moth tissues are significantly depleted in deuterium relative to irrigation water. (b) The δD value of water extracted from plants (solid triangles, dotted line), caterpillars (plus ‘+’ signs, barred-dotted line), and moths (open circles, barred line) was also linearly related to that of irrigation water (y_{plants H2O} = 0.73x+34.7, r² = 0.86; y_{caterpillar H2O} = 0.85x+46.8, r² = 0.94; y_{moth H2O} = 0.41x−19.2, r² = 0.44). Extracted water samples from plants, caterpillars and moths were enriched in deuterium relative to irrigation water. The slope of the relationships of the δD value of irrigation water to water extracted from plants and caterpillars did not differ significantly. The slope of the relationship between the δD value of irrigation and that of water extracted from moths was significantly shallower.</p

Carbon and nitrogen isotopic values of cabbage plants, caterpillars and moths were influenced by both trophic level and metamorphosis.

<p>There were no significant differences in δ¹³C values among plants and caterpillars, but moths were slightly (albeit significantly) depleted in ¹³C relative to both plants and caterpillars. In contrast, δ¹⁵N values increased significantly from plants to caterpillars to moths. Error bars denote SE.</p

Consumer to plant discrimination factors for caterpillars and moths of <i>Trichoplusia ni</i> fed on cabbage.

<p>Values are mean ±95% confidence intervals. Values labeled with NS are those for which the confidence interval overlaps with 0, whereas those labeled with * are those for which the 95% confidence interval for the mean does not include 0.</p

The δD values of moth (open circles, barred line) and caterpillar (plus ‘+’ signs, dotted line) tissues were linearly related to those of plant tissues and had a common slope.

<p>Note that moth organic material was significantly depleted in deuterium relative to that of caterpillars.</p