Relationships Between Survival Rate, Density, Population Trends, and Forage Destruction by Instars of Grasshoppers (Orthoptera: Acrididae)

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Abstract
Average daily rates of grasshopper survival were inversely related to density. For a hypothetical population of Melanoplus sanguinipes (F.), average survival rates of about 0.95 to 0.96 per day resulted in relatively uniform populations between generations; rates slightly above or below that range lead to drastic increases or decreases, respectively. There are reasonable combinations of daily survival rates and daily feeding rates that will allow any developmental stage within a generation of grasshoppers in the field to dominate utilization of forage by that generation. It is most probable, however, that the first three nymphal instars will be responsible for about 15 to 20% of the total forage utilization, and that adults will be responsible for both the greatest daily rate and the greatest proportion of utilization. Utilization by a nymphal instar is likely to exceed that of adults only under conditions of catastrophic population collapse.