• Cerodontha iridiphora;
  • ecological communities;
  • environment;
  • nitrogen;
  • herbivory;
  • Iris hexagona;
  • insect–plant interactions;
  • leaf mortality;
  • wetlands

Abstract 1. Salinity is an important cause of abiotic stress in wetland communities yet little is known about its consequences for freshwater plants and their insect herbivores. The goal of this study was to test the effect of salinity on a leafmining insect, Cerodontha iridiphora, and its herbaceous host plant, Iris hexagona.

2. Leafminer performance was evaluated on irises grown in control and saline treatments, and the effects of salinity and herbivory on leaf quality and mortality was measured.

3. Leafminer density and size were significantly lower on irises grown in saline water compared with freshwater.

4. Both salinity and herbivory accelerated leaf senescence and mortality, and their combined effects increased tissue loss by an order of magnitude compared with controls.

5. Leafminers acted as nutrient sinks. The undamaged regions of mined leaves contained 40% less nitrogen than unmined leaves, providing a mechanism for the premature leaf mortality.

6. Salinity was detrimental to the performance and survival of both the iris leafminer and its host plant. We propose that glycophytic host plants and their insect herbivores will suffer more than halophytic communities from environmental salinity because they lack the adaptive mechanisms to tolerate this potent physiological stress.