Examination of the food processes on mixed inferior host plants in a polyphagous grasshopper

Abstract The mass gain of polyphagous grasshoppers fed a mixture of intrinsically inferior plants is often greater than that of grasshoppers fed each inferior plant alone. We examined the cause of this greater mass gain by assessing the food processes of a polyphagous grasshopper in detail. Food processes were divided into five stages: consumption, fecal mass, assimilated food, approximate digestibility, and efficiency of conversion of digested food (ECD). Using final‐stadium female nymphs of the polyphagous grasshopper Parapodisma subastris , we compared the mass gain of nymphs fed the inferior plants Polygonum cuspidatum and Weigela hortensis or the superior plant Artemisia princeps . The mass gain of nymphs fed a single inferior plant was less than that of nymphs fed the superior plant because of reduced ECD. However, the mass gain of nymphs fed a mixture of the two inferior plants was not only greater than that of nymphs fed a single inferior plant, but also did not differ from that of nymphs fed the superior plant. Since consumption by nymphs fed the mixture was greater than that by nymphs fed P . cuspidatum and smaller than that by nymphs fed W . hortensis , and since the ECD of nymphs fed the mixture was greater than that of nymphs fed W . hortensis and was not different from that of nymphs fed P . cuspidatum , consumption and ECD appeared to cause the greater mass gain in nymphs fed the mixture.