Grasshoppers (Orthoptera: Acrididae) select vegetation patches in local‐scale responses to foliar nitrogen but not phosphorus in native grassland

Abstract

Key elements such as nitrogen (N) and phosphorus (P) are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small‐scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar‐N and ‐P in tallgrass prairie. Grasshopper densities were 67% greater in N‐fertilized plots but detected no effect to grasshopper densities from P‐fertilizer. Leaf damage to the dominant grass Andropogon gerardii was 32% greater in N‐fertilized plots, but no response to foliar‐P was detected. Herbivore damage to a common forb, goldenrod (Solidago missouriensis), was not strongly linked by fertilizer treatments, although there was increased leaf damage in N‐fertilizer treatments when no P was applied (a significant N × P interaction). Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar‐N in host plants with little evidence that P‐levels contribute to the spatial patterns.

Dietary phosphate affects food selection, post-ingestive P fate, and performance of a polyphagous herbivore

“…The ability of grasshoppers to obtain adequate P by foraging occasionally on high-P plants, and the negative effects of high-P diets, may explain why N but not P fertilization has been shown to affect grasshopper population densities in central North American grasslands, despite the observation that average foliar P concentrations available were in the range of those shown to be limiting to growth in this study (Loaiza et al, 2011). However, Joern et al (2012) found that plant P content was the most important element predicting overall grasshopper abundance in the central Nebraskan grasslands.…”

Not just the usual suspects: Insect herbivore populations and communities are associated with multiple plant nutrients

“…Second, grasshopper population densities fluctuate greatly in time or space, and communities vary in species composition at both local and regional scales (Joern and Gaines 1990, Lockwood 1997, Jonas and Joern 2007. Third, grasshopper densities or species compositions on a local scale are distributed spatially in a way that may reflect spatial heterogeneity in food quality (Heidorn and Joern 1987, White 1993, Haddad et al 2001, Loaiza et al 2011. We ask three primary questions: (1) How variable are plant foliar elemental concentrations between grasses and forbs, and between sites?…”

Effects of simulated and insect herbivory on nitrogen and protein precipitable phenolic concentrations of two legumes

“…Lower N availability can limit feed efficiency by reducing urea recycling and microbial efficiency in ruminants (Reed 1995) as reported for other forages containing CT (Mangan 1988). In grasshoppers, lower N availability is associated with reduced population densities because N is a limiting nutrient (Loaiza et al 2011). Additionally, N availability is a major driver of foliar damage by grasshoppers (Loaiza et al 2011).…”

“…In grasshoppers, lower N availability is associated with reduced population densities because N is a limiting nutrient (Loaiza et al 2011). Additionally, N availability is a major driver of foliar damage by grasshoppers (Loaiza et al 2011).…”