Salinity impacts biocontrol: a tri-trophic assessment of the effects of soil salinity on plant signaling and parasitoid fitness

Soil salinization and insect herbivory pose significant threats to global food security. While biocontrol agents like parasitoid wasps are a key pest management strategy, their efficacy may be compromised by abiotic stressors cascading through trophic levels. This study investigates the tri-trophic interactions among tomato plants (Solanum lycopersicum), the caterpillar pest Helicoverpa zea, and its specialist endoparasitoid Microplitis croceipes, under salinity stress. In Y-tube olfactometer assays, M. croceipes were significantly more attracted to herbivore-damaged plants grown under control conditions compared to those under salinity stress. While the volatile blend emitted by plants did not differ between treatments, shifts in volatile emissions of α-copaene, 3E-hexenol, methoxy phenyl oxime, and TMTT, likely influenced parasitoid choices. To determine whether these plant-mediated changes extended to host quality, we conducted separate behavioral and developmental assays. When presented with a choice, female wasps exhibited no oviposition preference between “non-salty” and “salty” hosts. However, the impact of salinity on parasitoid performance was stage-dependent with salinity stress significantly delaying larval development but not affecting offspring sex ratios. These findings suggest that salinity induces complex trade-offs between parasitoid attraction and fitness metrics, influencing top-down control exerted by parasitoids. This highlights the critical need for integrated frameworks that account for abiotic factors when designing biological control strategies for herbivore populations in saline environments.