Fertile pastures, feisty pests: exploring phosphorus effects on grass grub fitness

<p dir="ltr">Fertiliser applications are well-established tools in pasture-based agricultural landscapes. This study focuses on the impact of phosphorus (P) fertiliser on grass grub (<i>Costelytra giveni</i>), a major pasture pest. This research investigates the interplay between P, plant growth, and grass grub fitness in <i>Epichloë</i> endophyte-infected perennial ryegrass (<i>Epichloë</i> sp. LpTG-3 strain AR37) and meadow fescue infected with <i>E. uncinata</i> (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, and 78 mg L^-1), and grass grubs were introduced. Their survival, 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, 78 mg L^-1) and provided with identical plant material to assess their diet consumption and weight gain.</p><p dir="ltr">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. Similarly, 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.</p><p dir="ltr">The study underscores the pivotal role of selected <i>Epichloë</i> 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.</p>