Stage-based mortality of grassland grasshoppers (Acrididae) from wanderingspider (Lycosidae) predation

Mortality rates in insects, including grasshoppers (Acrididae), are often s tage- or size-specific. We estimated stage-specific mortality rates for thr ee common grasshopper species from a Nebraska (USA) sandhills grassland (Ag eneotettix deorum, Melanoplus sanguinipes and Phoetaliotes nebrascensis), a nd partitioned the impact due to wandering spider predation from remaining sources. Survivorship was estimated for multiple developmental stages (3rd instar through adult) under experimental conditions that either prevented o r permitted predation from free-living, wandering spiders (primarily Schizo cosa species). Total stage-specific mortality, including spider predation, examined over the period of single stages was greatest for the youngest sta ges (91 % for 3rd instar, 73 % for 4th instar, 63.5 % for 5th instar and 30 .4 % for adults). For the developmental stages considered and averaged for all species, the contribution to total mortality from spider predation over the 10-d period (approximately the length of a developmental stage) ranged from 17 % for 3rd instar nymphs to 23 % for 4th and 5th instars, and an un detectable level for adults. While spiders may depress grasshopper numbers, contributions from spider predation to grasshopper population dynamics are uncertain. (C) Elsevier, Paris.