A Model for Estimating Hatch and Mortality of Grasshopper Egg Populations Based on Soil Moisture and Heat1

Abstract

The study examined quantitatively the effects of soil moisture on embryonic development and egg mortality of a nondiapause strain of Melanoplus sanguinipes (Fabr.) With the type of soil used, a silty clay loam, a minimum soil moisture of ca. 13.5%, a little above the wilting point (11.7%), was necessary for eggs to complete development and hatch without experiencing any stress. This level of soil moisture was absolutely critical before blastokinesis. Embryonic development could proceed from oviposition until completion of anatrepsis at a soil moisture less than 13.5%. However, no further development would take place if this stress was not released by a higher level of moisture (≥ 13.5%). The rate of development after release of stress decreased as a function of the duration of moisture stress. A model based soil moisture and heat accounted for a maximum of 99% of the variance in hatching. An exponential decay curve was developed for the rate of egg mortality as a function of soil moisture to which they were exposed. This relationship explained 83% of the variance in the rate of mortality.