Reductions in foliar Hemiptera in portions of a fescue grassland invaded by Smooth Brome (Bromus inermis)

Résumé

Fescue grassland in Canadian prairie is characterized by Plains Rough Fescue (Festuca hallii), but the introduced exotic grass, Smooth Brome (Bromus inermis), is expanding therein. Hemiptera play an important role as herbivores in vegetation. In an invaded fescue grassland in Manitoba, 52 plant species had a combined average cover of 216%. Kentucky Bluegrass (Poa pratensis), another exotic grass, was most abundant at 64%, followed by B. inermis at 21% and the native grass F. hallii at 18%. Across 47 random sample points, B. inermis cover ranged from 0% to 180%. At these points, 2445 specimens of Hemiptera were collected by sweep net and divided into 99 morphologically distinct species. Bromus inermis cover had negative correlations with Hemiptera species richness and diversity, but not with abundance and biomass of Hemiptera. However, B. inermis cover was negatively correlated with abundance of two individual species of Hemipteran leafhoppers in the family Cicadellidae: Doratura stylata and Diplocolenus configuratus. Total graminoid cover had no significant correlation with any of the above Hemiptera variables. We conclude that feeding requirements deter some phytophagous Hemiptera from entering sections of fescue grassland invaded by B. inermis. In this way, invasion by B. inermis can be expected to modify ecosystem function by increasing feeding pressure on neighbouring natural vegetation and other introduced species.