Moisture content in a wheat germ diet and its effect on the growth of Plodia interpunctella (Hübner)

The growth rate of Plodia interpunctella larvae feeding on wheat germ was highly dependent upon the water content in the diet. The water content in a cereal diet is established by the hygroscopicity of the dietary components and the relative humidity (r.h.) in the equilibrating atmosphere. The larval growth rates on wheat germ increased with corresponding increases in r.h. over the range of 40–85%. Similar changes in r.h. had a measurable, albeit minimal, impact on the time required for embryonic development and egg hatch. The water content of wheat germ was further increased by supplementing the germ with the humectant, glycerol. The larval growth rate increased with each incremental increase in dietary water content irrespective of whether it resulted from increases in r.h. or glycerol. However, glycerol supplementation provided an additional boost to the growth rate that was in addition to and distinct from the dietary water increase.