TEMPORAL PATTERNS IN FEEDING OF GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE) - IMPORTANCE OF NOCTURNAL FEEDING

Rangeland grasshoppers were sampled from the Western High Plains ecore gion every 6 h over 2 periods of 2 d each during September 1992. The c rop contents of the grasshoppers were classified as full (>80% filled) , partially full (5-80% filled), or empty (<5% filled). Rangeland spec ies often engaged in nocturnal feeding, in some cases more commonly th an diurnal feeding. Across all species, 44% of individuals captured at midnight and sunrise had full crops, compared with 41% captured at mi dday and sunset. The frequencies of full and not-full (partially full and empty) crops across sampling times differed significantly between species and between sexes within 4 of the 5 dominant species. Laborato ry bioassays of the rate of food (dyed filter paper) passage in field- collected grasshoppers, at 10, 21, and 32 degrees C during light and d ark conditions, revealed that crops were emptied within 4 h of feeding . Seasonal and spatial variation in temporal feeding was studied at 3 sites in July August, and September 1994. The temporal patterns of cro p fullness differed significantly among species and sexes at each samp ling location and date, The frequencies of full crops also differed si gnificantly within males and females of most species between sampling dates (at a single site) and between sites (at a single date). Tempora l feeding patterns were highly variable. Four types of feeding pattern s were apparent: diurnal, nocturnal, continuous, and intermittent. Tem poral niche partitioning resulted in constant feeding by a grasshopper assemblage. Nocturnal feeding was an important component of this part itioning; 78% of the classified cases involving substantial nocturnal feeding and 50-75% of all grasshoppers sampled had frill crops at midn ight and sunrise.