Arthropod Faunas of Monocultures and Polycultures in Reseeded Rangelands

Abstract

Sap-feeding and predaceous arthropod faunas of forage bunchgrasses in reseeded rangeland vegetation were examined. Four major species of sap feeders were found; the major predators were spiders. Grass monoculture had very high densities of sap feeders compared with grass biculture, shrub-grass, tree-grass, and native areas; this was reflective of the large contribution from the mirids Irbisia brachycera Uhler and Conostethus americanus (Knight). They were present during the leaf stages of crested wheatgrass when it had its lowest carbohydrate root reserves. Homoptera and predator densities were not significantly related to the pattern of vegetation. The lowest number of sap-feeder species occurred in the grass monoculture, and sap-feeder faunas in this plot were dissimilar to those of all other plots. One-season dispersal experiments did not support the hypothesis that grass density caused the differences between arthropod faunas in different vegetation, whereas big sagebrush, common in reseeded pastures, repelled I. brachycera during short-term dispersal. The data indicate that reseeding to monocultures may result in high densities of Miridae during the leaf stages compared with moderate densities of Homoptera during the flower and seed stages in bicultures. The implications for pest management are discussed.