OOS 13-5 - Bats, bugs and pecans: The role of insectivorous bats in a pecan agroecosystem in central Texas

Tuesday, August 9, 2011: 9:20 AM
16A, Austin Convention Center
Elizabeth C. Braun de Torrez, Center for Ecology and Conservation Biology, Department of Biology, Boston University, Boston, MA, Veronica A. Brown, Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN, Thomas H. Kunz, Center for Ecology and Conservation Biology, Boston University, Boston, MA and Gary F. McCracken, Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN

Bats are commonly recognized for their voracious appetites for nocturnal/crepuscular insects; however, little is known about specific prey items or the degree to which they suppress arthropod pests. Pecan trees (Carya illinoinensis), native to the U.S. and Mexico, are economically important for both local farmers and international export. The pecan nut casebearer moth (PNC), Acrobasis nuxvorella, is arguably the most devastating insect pest of pecans, damaging up to 85%. Anecdotal evidence has suggested that bats suppress this pest; however, our research is the first to explore this. In this study, we investigated the habitat use and diversity of bats in the pecan agroecosystem and the patterns of PNC consumption by bats in central Texas. We captured bats with mist nets in three landscape types: 1) native organic orchards, 2) conventional orchards and 3) natural mesquite/juniper woodlands and monitored PNC abundance in each site with pheromone traps. Fecal samples were obtained by holding bats in cloth bags for up to three hours following capture. To document the relative consumption of PNC moths by bats, we used quantitative-PCR (qPCR). Total DNA was extracted from guano and a species-specific primer was used to amplify the PNC CO1 gene. DNA from PNC was quantified with Opticon-Monitor 3 software through comparison to a size standard.


Bat activity and diversity of bats was higher within pecan orchards than in the surrounding semi-arid landscape, demonstrating that pecan orchards provide important habitat for bats. Abundance of PNC peaked sharply several times throughout the season. We analyzed 401 samples from individual bats using qPCR. Our results indicate that PNC moths were consumed by five species of bats captured in the orchards: Tadarida brasiliensis, Myotis velifer, Nycticeius humeralis, Lasiurus borealis and Perimyotis subflavus; however, both frequency of occurrence (#positive/total bats) and relative quantity (#gene copies/bat) of PNC in the diet varied by bat species. Frequency of occurrence ranged from 2.1% (N. humeralis) to 22.9% (L. borealis). The highest relative quantity of PNC was also found in the diet of L. borealis. There were not enough positive samples to analyze consumption differences by functional group or landscape type; however, only bats captured in pecan orchards had consumed PNC. Temporally, consumption was concentrated around nights of peak PNC activity. Our results show clear differences in PNC consumption between species, perhaps indicating differences in foraging behavior, and illustrate the importance of encouraging high bat diversity in pecan orchards to reduce insect pest populations.

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