Background/Question/Methods    Insectivorous bats have been postulated to play vital, yet largely unexplored, roles in ecosystem function by suppressing certain agricultural pests. Knowledge of bat activity and diversity in human-altered landscapes is crucial for understanding this expected ecosystem service. In Texas, agriculture has significantly modified native woodland savanna, and pecan cultivation has replaced diverse riparian woodlands. The pecan nut casebearer (Acrobasis nuxvorella) and the hickory shuckworm (Cydia caryana) are two of the most devastating insect pests affecting pecans and are thought to be preyed upon by bats.  In our study, we documented habitat use by bats within the pecan agroecosystem to evaluate: 1) the role of pecan orchards as a source of riparian woodland habitat for bats, 2) the influence of management intensity on bat activity and diversity, and 3) temporal and spatial interactions of bats and pests within these orchards.  Fieldwork was conducted in San Saba, Texas (summer 2008).  Sites were divided into three habitat types: 1) organic pecan groves, 2) commercial plantations, and 3) unmanaged juniper/mesquite woodlands.  Bat activity and diversity were monitored with mist nets and AnabatII acoustic detectors. Roosting behavior of bats and emergences of insect pests were tracked with thermal imaging cameras and pheromone traps, respectively.     Results/Conclusions  Five bat species were captured in the pecan-dominated agroecosystem: Tadarida brasiliensis, Myotis velifer, Nycticieus humeralis, Lasiurus borealis, and Perimyotis subflavus.  Results of mist netting revealed that the abundance of adult bats was significantly higher in organic orchards than in commercial plantations and natural woodlands. Alpha diversity and evenness of bat species were also highest in the organic orchards and lowest in the unmanaged woodlands. We found a significant association between bat species and habitat type, with three of the four most abundant taxa showing clear habitat preferences. The Brazilian free-tailed bat (T. brasiliensis) whose ecosystem services have been demonstrated in Texas cotton production, was found only in organic orchards and natural woodlands.  Preliminary analysis of acoustic data supports the mist-netting results for habitat use; however, there is substantial temporal variation. Bat activity increased with proximity to the river, but only significantly within 100 meters.  Colony dynamics and bat activity in the orchards did not seem to reflect pest emergence peaks; however, more analysis is required. This initial study of habitat use by bats directly compliments other work we are conducting to examine bat-mediated trophic interactions within pecan orchards and their cumulative ecological and economic impact on pecan pests.