Nutrient dilution and climate cycles underlie declines in a dominant insect herbivore

Proc Natl Acad Sci U S A. 2020 Mar 31;117(13):7271-7275. doi: 10.1073/pnas.1920012117. Epub 2020 Mar 9.


Evidence for global insect declines mounts, increasing our need to understand underlying mechanisms. We test the nutrient dilution (ND) hypothesis-the decreasing concentration of essential dietary minerals with increasing plant productivity-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 Niño 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 2.1-2.7%/y. Climate cycle indices of spring ENSO, summer NAO, and winter or spring PDO accounted for 40-54% 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-nutrients which limit grasshopper abundance-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-habitat loss, light and chemical pollution-ND may be widespread in remaining natural areas.

Keywords: Acrididae; global change; grasshopper; grassland; insect decline.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Biomass
  • Climate Change / statistics & numerical data
  • Conservation of Natural Resources / trends*
  • Demography / trends*
  • Ecosystem
  • El Nino-Southern Oscillation
  • Grasshoppers*
  • Grassland
  • Herbivory
  • Insecta
  • Kansas
  • Nutrients
  • Poaceae
  • Seasons
  • Weather

Associated data

  • figshare/10.6084/m9.figshare.11862483
  • figshare/10.6084/m9.figshare.11862459