Assimilation of Rubidium by Melanoplus Grasshoppers (Orthoptera: Acrididae)

A series of assays were set up to evaluate several parameters affecting rubidium assimilation, excretion and effects on migratory grasshopper, Melanoplus sanguinipes (F.), development following ingestion of RbCl. Dosages of RbCl as high as 3.82 mg were found to elevate tissue concentrations of Rb as much as 4,900 ppm above background levels at 2 d after ingestion. The rate of ingestion was essentially linear, and excretion rates followed the behavior of a half-life model with a half-life of roughly 1 d. There were no differences between M. sanguinipes and M. packardii (Scudder) in the amount of Rb assimilated, however, subtle differences that were proportional to the weight of the grasshoppers were observed in the resulting tissue concentrations. Constant exposure to RbCl raised body concentrations of Rb to 2,000–5.000 ppm and caused a slight retardation in developmental rates. A single exposure to 121μg of RbCl caused tissue concentrations of Rb to rise to 140ppm at 2 d after ingestion, but had no effect on developmental rates. These assays provide the basic parameters necessary for designing field studies in which RbCl, formulated in a bait, can be used for grasshopper dispersal and feeding studies.