H. zea caterpillars prefer to feed on tomato plants treated with a lower concentration of salt
In petri dish-based choice assays, H. zea caterpillars preferred to feed on tomato plant leaf discs treated with the least amount of salt. In a two-choice assay, percent leaf area consumed by H. zeacaterpillars was significantly higher in no-salt (0 mM) plant tissue compared to high salt plant tissue (200 mM) (Figure 3A; t = 4.861, df = 34, P < 0.001) and moderate salt plant tissue (100 mM) compared to high salt plant tissue (200 mM) (Figure 3A; t = 4.107, df = 25, P = 0.0004). However, caterpillars did not show significant consumption differences between 0 mM and 100 mM plant tissue (Figure 3A; t = 0.3521, df = 35,P = 0.7268). Caterpillars were observed to completely consume plant tissue treated with the least amount of salt first (first finish) (Figure 3B ; 0-200: χ² = 25,P < 0.0001; 100-200: χ² = 16.333, P < 0.0001; 0-100: χ²= 4.172, P = 0.0411).
In a three-choice assay, the percentage leaf area consumed by H. zea caterpillars decreased significantly from 64.97 ± 5.873% in 0 mM to 39.67 ± 4.255% in 100 mM to 16.99 ± 1.298% in 200 mM treatments (Figure 3C; χ² = 37.93, P < 0.0001, Dunn’spost-hoc all P < 0.05). H. zeacaterpillars did not choose to feed or establish on any leaf preferentially at first (Figure 3D; First establish (FE): χ² = 1.310, df = 2, P = 0.5194); however, they showed differences in feeding over time. Caterpillars finished 0 mM leaves first, followed by 100 mM leaves (Figure 3E; First finish (F1): χ² = 35.429, df = 2, P< 0.0001; Second finish (F2): χ² = 20.222, df = 2, P< 0.0001). Refer to Supplementary Figure S1 andSupplementary Figure S2 for photographs of first finishes and leaf area consumption in the assay.