Pollinator Abundance in Semiarid Pastures as Affected by Forage Species

The semiarid Texas High Plains has a declining water supply for irrigated crop production because of unsustainable pumping from the Ogallala aquifer. Conversion of land from annual crops to limited-irrigated perennial forages is an option for profitable land use. VW-B. Dahl' old world bluestem [Bothriochloa bladhii (Retz) S.T. Blake, OWB] is a well-adapted grass known for deterring some soil-dwelling insects, but effects of OWB on insect pollinators are unknown. The aim of this study was to determine whether adapted forage types (species or mixtures) affected insect pollinator abundance in pastures. Foraging insects were collected using bee bowls and compared among OWB alone, OWB mixed with alfalfa (Medicago sativa L.), alfalfa, and a native grass mix. Twentyone families from four orders of insects were recovered over 3 yr. Sweat bee (Hymenoptera: Halictidae) was the most abundant family, with 59% of the total number of insects collected. Honey bees (Hymenoptera: Apidae) constituted an additional 17% of the total number of insects collected, with hover flies (Diptera: Syrphidae) and skippers (Lepidoptera: Hesperiidae) found in lesser abundances. Interactions between forage type and years restricted consistent forage-type effects. In general, the lowest abundances of foraging insects were commonly found in OWB growing alone, especially of the native, ground-nesting sweat bee, whereas greater abundances were more commonly found in native grass and alfalfa pastures. Widespread adoption of WW-B.Dahl OWB may reduce local numbers of foraging insects in the Texas High Plains, which could negatively affect pollinators in managed grasslands.