The Effects of Prey Abundance and Bt (Bacillus thuringiensis) Crops on Bat Activity in South-Central Texas Agroecosystems
Date of Award
Master of Science
Ecology and Evolutionary Biology
Gary F. McCracken
Thomas G. Hallam, Nathan Sanders
Agroecosystems produce insects in great abundance, with episodic irruptions in time, and patchy distributions in space. In the industrial scale agroecosystems of south-central Texas, millions of Brazilian free-tailed bats (Tadarida brasiliensis) consume these insect pests. In the past decade, growers in Texas have planted transgenic Bt (Bacillus thuringiensis) crops on a large scale, which may reduce populations of target insect species by up to 95%. To investigate potential impacts of this evolving agricultural landscape on insectivorous bats, I examined the response of foraging bats to emergences of insects from replicate Bt and non-Bt fields of corn and cotton in the Winter Garden region of south-central Texas. I quantified bat activity using ultrasonic detectors deployed simultaneously in Bt and non-Bt fields. I measured insect activity using pheromone traps and video imaging. Professional crop consultants scouted fields to determine dates of insect emergence. We recorded 92% more echolocation calls, 62% more AnaBat files, and 257% more feeding buzzes over agricultural fields during periods of local insect emergence. During these insect emergence periods, bat activity was correlated with the abundance of moths and negatively related to the distance between foraging sites and roosting sites. In general, Bt crops did not have a measurable impact on the activity of bats except at one site where moths were more abundant over non-Bt crops versus Bt crops. Foraging bats showed a delayed response to moth abundance, which is consistent with the hypothesis that roosts serve as information centers that enhance foraging efficiency. The ability of millions of bats to exploit localized patches of prey across a large area provides further evidence of their pest control service. This economically important pest control service extends beyond growers in Texas, as the populations of moths produced in agroecosystems in Texas influence agricultural production on a continental scale.
Kennard, Kimberly S., "The Effects of Prey Abundance and Bt (Bacillus thuringiensis) Crops on Bat Activity in South-Central Texas Agroecosystems. " Master's Thesis, University of Tennessee, 2008.