@article {KNZ002005,
	title = {Nutrient dilution and climate cycles underlie declines in a dominant insect herbivore},
	journal = {Proceedings of the National Academy of Sciences},
	volume = {117},
	year = {2020},
	pages = {7271-7275},
	abstract = {<p>Evidence for global insect declines mounts, increasing our need to understand underlying mechanisms. We test the nutrient dilution (ND) hypothesis\&mdash;the decreasing concentration of essential dietary minerals with increasing plant productivity\&mdash;that particularly targets insect herbivores. Nutrient dilution can result from increased plant biomass due to climate or CO2 enrichment. Additionally, when considering long-term trends driven by climate, one must account for large-scale oscillations including El Ni{\~n}o Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). We combine long-term datasets of grasshopper abundance, climate, plant biomass, and end-of-season foliar elemental content to examine potential drivers of abundance cycles and trends of this dominant herbivore. Annual grasshopper abundances in 16- and 22-y time series from a Kansas prairie revealed both 5-y cycles and declines of 2.1\&ndash;2.7\%/y. Climate cycle indices of spring ENSO, summer NAO, and winter or spring PDO accounted for 40\&ndash;54\% of the variation in grasshopper abundance, mediated by effects of weather and host plants. Consistent with ND, grass biomass doubled and foliar concentrations of N, P, K, and Na\&mdash;nutrients which limit grasshopper abundance\&mdash;declined over the same period. The decline in plant nutrients accounted for 25\% of the variation in grasshopper abundance over two decades. Thus a warming, wetter, more CO2-enriched world will likely contribute to declines in insect herbivores by depleting nutrients from their already nutrient-poor diet. Unlike other potential drivers of insect declines\&mdash;habitat loss, light and chemical pollution\&mdash;ND may be widespread in remaining natural areas.</p>},
	keywords = {LTER-KNZ},
	issn = {0027-8424},
	doi = {10.1073/pnas.1920012117},
	url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1920012117},
	author = {Welti, Ellen A.R. and Roeder, Karl A. and de Beurs, Kirsten M. and Anthony Joern and Kaspari, Michael}
}
