Caterpillar petri dish choice assay
To determine caterpillar preference for plant tissue with different levels of salt stress, we conducted three two-choice assays and one three-choice assay (Figure 1B ):
  1. No salt-treated plant leaf disc (0 mM) vs. High salt-treated plant leaf disc (200 mM).
  2. Medium salt-treated plant leaf disc (100 mM) vs. High salt-treated plant leaf disc (200 mM).
  3. No salt-treated plant leaf disc (0 mM) vs. Medium salt-treated plant leaf disc (100 mM).
  4. No salt-treated plant leaf disc (0 mM) vs Medium salt-treated plant leaf disc (100 mM) vs High salt-treated plant leaf disc (200 mM) (Panet al. , 2019).
1.5 cm diameter leaf discs were excised from the fourth fully expanded leaf of each treatment plant (0 mM, 100 mM, and 200 mM). One leaf disc from each treatment was placed at opposite ends of a petri dish (10 cm X 1.5 cm) lined with 3% agar. A single 2nd instarH. zea caterpillar was placed inside the petri dish, and the petri dishes were sealed with parafilm to prevent the desiccation of herbivores and plant tissue (Marsack and Connolly, 2022). Caterpillars were given thirty minutes to make a choice in the petri dish, after which the leaf disc the caterpillar had settled on was recorded. This was referred to as the “first establish” (FE) parameter. Another parameter called the “first finish” (F1) was reported as the first leaf disc to be totally consumed by the caterpillar (Supplementary Figure S1 ). In the three-choice test, a “second finish” (F2) was also recorded, which was the second leaf disc to be completely consumed by the caterpillar. First and second finishes were recorded for a maximum of five days. After two days of feeding, leaf area consumed or caterpillar consumption rate was determined by photographing the remaining leaf disc area and analyzing images in ImageJ (Supplementary Figure S2 )(Glozer, 2008; Connolly, Guiden and Orrock, 2017; Orrock et al. , 2018; Marsack and Connolly, 2022).