Synthetic odorants

Synthetic odorants were purchased from Sigma-Aldrich unless otherwise specified at the highest purity. Odorants were diluted in either molecular grade water or paraffin oil (PO) to 1% v/v before use.

We identified the volatiles of caterpillars feces using SPME coupled with GC/MS. One gram of feces from caterpillars raised on either D. wrightii or N. attenuata was put into a 500-mL plastic container. A circular filter paper (12-mm diameter, Whatman; Sigma–Aldrich) loaded with 10 μL of diluted bromodecane (1:10⁴ in hexane) was used as an internal standard. Through a hole in the lid of the container, a SPME fiber (50 μm of divinylbenzene/carboxen/polydimethylsiloxane coating; Supelco) was exposed to the container headspace for 30 min at room temperature without agitation, and then introduced into the injector inlet for 2 min at 250 °C in split-less mode. The compounds adsorbed on the fiber were then analyzed by GC/MS (GC: Agilent 6890, Agilent; MS: 5975C MS, Agilent). After fiber insertion, the column temperature was maintained at 40 °C for 2 min and then increased to 260 °C at 15 °C⋅min⁻¹, followed by a final stage of 5 min at 260 °C. Compounds were identified by comparing mass spectra against synthetic standards and NIST 2.0 library matches. All of the synthetic odorants that were tested and confirmed were purchased from Sigma–Aldrich (https://www.sigmaaldrich.com/).