The increasing expenses and environmental repercussions associated with phosphorus (P) fertiliser underscore the necessity for precision-managed application methods. These changes affect pastoral systems, where cool-season grasses like perennial ryegrass and meadow fescue form beneficial relationships with Epichlo & euml; endophytes. Understanding how fertilisers influence these endophytes, host grasses, and insect pests is crucial, as Epichlo & euml; endophytes enhance resistance to some herbivorous insects. This study examined the indirect impact of various P fertiliser regimes on cool-season grasses, which serve as food sources for porina larvae (Wiseana copularis), a significant pasture pest in New Zealand. Endophyte-infected (Epichlo & euml; sp. LpTG-3 strain AR37) perennial ryegrass and meadow fescue infected with E. uncinata (strain MaxR (AR1017)), alongside their endophyte-free counterparts were grown in P-enriched soil with varying Olsen P levels (9, 18, 28, and 78 mg/L). Freeze-dried foliage was added to semi-synthetic diets and fed to porina larvae in a no-choice assay. Measurements included diet consumption, porina survival, weight gain. Measurements in foliage included fungal alkaloid concentration, fungal biomass, and plant nutrient levels. Endophyte infection of AR37 and MaxR significantly reduced porina diet consumption, larval weight gain and survival irrespective of soil Olsen P levels to the plant. Loline alkaloid concentration in MaxR-infected herbage increased with increasing soil Olsen P levels while fungal mass remained unchanged. In endophyte-free grasses, porina larvae significantly increased their diet consumption, weight gain and survival as the Olsen P level available to the host plant increased. While endophyte strains AR37 and MaxR continue to protect their hosts under different Olsen P regimes, these results suggest that the improved performance of porina on endophyte-free plants is largely driven by P-induced changes in food quality. Here, we discuss the implications of porina damage in New Zealand pastures in the context of decreasing P availability.

BACKGROUND: Fertiliser applications are well-established tools in pasture-based agricultural landscapes. This study focuses on the impact of phosphorus (P) fertiliser on grass grub (Costelytra giveni), a major pasture pest. This research investigates the interplay between P, plant growth, and grass grub fitness in Epichlo & euml; endophyte-infected perennial ryegrass (Epichlo & euml; sp. LpTG-3 strain AR37) and meadow fescue infected with E. uncinata (strain MaxR; AR1017), alongside their endophyte-free counterparts. In a glasshouse trial, plants were grown in P-enriched soil with varying Olsen P levels (9, 18, 28 or 78 mg L-1), and grass grubs were introduced. Their survival and weight gain, and plant performance were measured. In a bioassay, grass grubs were placed in specimen vials with P-enriched soils (Olsen P levels 9, 18, 28 and 78 mg L-1) and provided with identical plant material to assess their diet consumption and weight gain. RESULTS: In the glasshouse trial, results highlighted a notable decrease in the survival of grass grub on plants infected with MaxR endophyte, but not with AR37, as well as increasing soil Olsen P levels in both plant species. While grass grub decreased plant performance at the low Olsen P level (9 mg L-1), this effect diminished with increasing P. Likewise, results from the bioassay showed a decrease in diet consumption with increasing soil Olsen P levels. In both trials increasing Olsen P levels correlated with diminished grass grub performance, revealing a nuanced relationship between soil fertility and pest dynamics. CONCLUSION: The study underscores the pivotal role of selected Epichloe endophyte-grass associations in mitigating grass grub damage across varying phosphorus levels. This study highlights the potential to integrate P applications for sustainable pest control against grass grub. Further field trials are required to validate these findings. (c) 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.