Arthropod Community Composition of 'WW-B.Dahl' Old World Bluestem Pasture Systems.

The Texas High Plains has limited water supply for irrigation to produce agricultural crops and livestock. ‘WW-B.Dahl’ Old World bluestem [OWB, Bothriochloa bladhii] is a highly productive, drought-tolerant grass in dryland and limited-irrigation conditions. Some varieties of OWB are rich in essential (volatile) oils which confer a pleasant smell and are suspected of deterring some insects. We characterized the size and structure of the above-ground arthropod communities in different pasture treatments by using pitfall traps. Fly ratings on cattle in 2014 were lower (P<0.01) for OWB alone than for OWB+alfalfa. Fly ratings in 2015 increased over time, but did not differ (P=0.16) between pasture treatments. Pastures containing OWB had fewer ground-active arthropods (P<0.01) than alfalfa and native mix in 2014 and 2015. Numbers of red imported fire ants (Solenopsis invicta Buren, RIFA) and harvester ants (Pogonomyrmex badius) were greatest in the native mix and near zero in pastures containing OWB both in 2014 and 2015.  The presence of OWB essentially eliminated fire ants/harvester ants from the community of ground-dwelling arthropods. Teff and alfalfa had fewer fire ants (P<0.01) than the native mix pastures. Most of the difference among pasture types in total arthropods is explained by the differences in RIFA and harvester ants. Notably, there was no difference among pasture types in beneficial insect numbers. FAMEs for Soil microbial communities were highest in OWB+alfalfa followed by OWB alone at 0-5 cm and 5-15 cm depths. Alfalfa had the lowest FAMEs followed by native mix at 0-5 cm and 5-15 cm depths. Use of WW-B.Dahl OWB in pastures effectively controls the undesirable RIFA communities while still hosting desirable native insects and high levels of soil microbial biomass. Further research should test links between essential oil presence and insect deterrence on cattle and in the soil-plant biome.