The effects of kochia, wheat and oats on digestive proteinases and the protein economy of adult grasshoppers, Melanoplus sanguinipes

Abstract Adult male grasshoppers ( Melanoplus sanguinipes ), fed diets of wheat, oats or kochia ad libitum varied in the amount of food consumed wheat > oats > kochia which paralleled weight gains but not the amount of frass produced. Approximate digestibility was significantly lower, and the efficiency of conversion of assimilated food was significantly higher on kochia than either of the cereals. Assays of proteolytic digestive enzymes on the three diets revealed that adults produced substantially more trypsin and chymotrypsin on oats and kochia than on wheat. Production of greater amounts of these enzymes occurred within seven days after introduction to oats or kochia. Electropherograms of haemolymph from grasshoppers fed oats or kochia had much less stainable protein compared to those fed wheat. All putative bands of vitellogenin from either haemolymph or fat body were substantially reduced on diets of oats or kochia. In the male reproductive system, the major accessory gland protein, long hyaline gland protein, was significantly reduced in kochia-fed grasshoppers. Leaves of wheat had significantly more precipitable protein than oats, and oats had significantly more precipitable protein than kochia. Measurable protein in the three diets may not completely account for the disparities in vitellogenins and other haemolymph proteins. It is suggested that the overproduction of digestive proteolytic enzymes may have been a contributory factor in protein attrition, resulting in slower growth and reduced reproduction. These observations explain in part the consequences of these diets to the biotic potential of grasshoppers.