Grasshopper egg mortality mediated by oviposition tactics and fire intensity

Abstract

Abstract 1. It is commonly assumed that arthropod species living or hibernating in the soil would not be affected by grassland fires, even though burning results in elevated surface and below‐ground soil temperatures. The importance of elevated below‐ground soil temperatures during fires on the survival of grasshopper eggs had not been examined.2. The effects of simulated autumn grassland fires of varying intensities on below‐ground egg mortality were examined with grasshopper species laying shallow egg pods (Ageneotettix deorum) and deeper egg pods (Melanoplus sanguinipes) to test the hypothesis that exposure to heat during fires was the mechanism responsible for population reductions in A. deorum following fire.3. Species‐specific oviposition characteristics mediated the effects of fire intensity on below‐ground egg mortality. The results indicate that fires occurring in areas with at least 3100 kg ha−1 standing crop biomass would be expected to significantly reduce populations of A. deorum, but not M. sanguinipes. No A. deorum eggs hatched in 12 of the 14 oviposition containers subjected to simulated fires approximating a standing crop biomass of 4500 kg ha−1. This is the first study to link field observations of rangeland insect populations following fire to mechanisms related to below‐ground egg mortality.