Temporal Patterns in Feeding of Grasshoppers (Orthoptera: Acrididae): Importance of Nocturnal Feeding

Abstract

Rangeland grasshoppers were sampled from the Western High Plains ecoregion every 6 h over 2 periods of 2 d each during September 1992. The crop contents of the grasshoppers were classified as full (>80% filled), partially full (5–80% filled), or empty (>5% filled). Rangeland species often engaged in nocturnal feeding, in some cases more commonly than diurnal feeding. Across all species, 44% of individuals captured at midnight and sunrise had full crops, compared with 41% captured at midday 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. Laboratory bioassays of the rate of food (dyed filter paper) passage in field-collected grasshoppers, at 10, 21, and 32°(; during light and dark 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 crop fullness differed significantly among species and sexes at each sampling location and date. The frequencies of full crops also differed significantly within males and females of most species between sampling dates (at a single site) and between sites (at a single date). Temporal feeding patterns were highly variable. Four types of feeding patterns were apparent: diurnal, nocturnal, continuous, and intermittent. Temporal niche partitioning resulted in constant feeding by a grasshopper assemblage. Nocturnal feeding was an important component of this partitioning; 78% of the classified cases involving substantial nocturnal feeding and 50–75% of all grasshoppers sampled had full crops at midnight and sunrise.