Figure 1

Evolutionary interactions among trophic levels influencing chemical defensive strategies in phytophagous insects. Phytophagous insects are held in ‘ecological pincers’ consisting of top–down as well as bottom–up selective pressures in the case of host plants containing deleterious chemicals (red arrows). However, the insects may sequester plant compounds, and/or produce defensive chemicals themselves, and they can also combine chemical with non-chemical defensive traits, which are all traits eventually used upon attack by natural enemies (green arrows).