THE INFLUENCE OF SOIL MOISTURE ON SURVIVAL OF EGGS OF THE PRAIRIE GRAIN WIREWORM, CTENICERA DESTRUCTOR

Abstract Extreme differences in survival of eggs of Ctenicera destructor (Brown) were observed when eggs were placed at depths ranging from 1/2 to 4 in. in the soil in the field. These differences were closely related to the soil moisture variations recorded during different seasons. Eggs that had absorbed water before being placed in the field were much more resistant to desiccation than those that had not absorbed water. In the laboratory, eggs absorbed water, developed and hatched in soil dried to a constant moisture level of 8.2% (dry weight basis) at 98% R.H., but were unable to absorb water from soil dried to moisture equilibrium at 96.6% R.H., or from soil wetted to moisture equilibrium at 98% R.H. Some water was absorbed by eggs placed in air at 98% R.H., but this was insufficient for normal development and hatching. The soil moisture tension of soil dried to moisture equilibrium at 98% R.H. was calculated as approximately 31 atmospheres. It is evident that eggs are able to develop remarkably high internal suctions in order to absorb water from such soil. Both the field and laboratory results showed that in drying soil, the lower limit of soil moisture at which eggs could absorb water was about 8%, considerably below the permanent wilting percentage (9.9%) of the soil used in these studies.