Brazilian Free‐tailed Bats as Insect Pest Regulators in Transgenic and Conventional Cotton Crops

Abstract

Abstract. During the past 12 000 years agricultural systems have transitioned from natural habitats to conventional agricultural regions and recently to large areas of genetically engineered (GE) croplands. This GE revolution occurred for cotton in a span of slightly more than a decade during which a switch occurred in major cotton production areas from growing 100% conventional cotton to an environment in which 95% transgenics are grown. Ecological interactions between GE targeted insects and other insectivorous insects have been investigated. However, the relationships between ecological functions (such as herbivory and ecosystem transport) and agronomic benefits of avian or mammalian insectivores in the transgenic environment generally remain unclear, although the importance of some agricultural pest management services provided by insectivorous species such as the Brazilian free-tailed bat, Tadarida brasiliensis, have been recognized.We developed a dynamic model to predict regional-scale ecological functions in agricultural food webs by using the indicators of insect pest herbivory measured by cotton boll damage and insect emigration from cotton. In the south-central Texas Winter Garden agricultural region we find that the process of insectivory by bats has a considerable impact on both the ecology and valuation of harvest in Bacillus thuringiensis (Bt) transgenic and nontransgenic cotton crops. Predation on agricultural pests by insectivorous bats may enhance the economic value of agricultural systems by reducing the frequency of required spraying and delaying the ultimate need for new pesticides. In the Winter Garden region, the presence of large numbers of insectivorous bats yields a regional summer dispersion of adult pest insects from Bt cotton that is considerably reduced from the moth emigration when bats are absent in either transgenic or non-transgenic crops. This regional decrease of pest numbers impacts insect herbivory on a transcontinental scale. With a few exceptions, we find that the agronomics of both Bt and conventional cotton production is more profitable when large numbers of insectivorous bats are present.

Interactions among predators and the cascading effects of vertebrate insectivores on arthropod communities and plants

“…The metaanalysis of Van Bael et al (9), which was based upon a subset of the data presented here (n = 48 studies), found parallel results for bird effects on predaceous and herbivorous arthropods in trees and understory shrubs. Although negative effects of vertebrate insectivores on arthropod predators may arise in part from competition for a shared prey base of herbivores, diet studies clearly demonstrate that vertebrate insectivores also directly consume predatory arthropods (10,19,20). This first result-that vertebrate insectivores act as intraguild predators, suppressing both intermediate predators and herbivores-thus sets the stage for our test of the subsequent predictions.…”

Bats in the Anthropogenic Matrix: Challenges and Opportunities for the Conservation of Chiroptera and Their Ecosystem Services in Agricultural Landscapes

“…The trickle-down impacts on agricultural production could be substantial, although quantitative evidence is lacking. The effects of GM crops incorporating insecticidal traits have been investigated largely in the context of the provisioning of predation services (Federico et al 2008;Lopez-Hoffman et al 2014; see next section); however, declines in pest numbers associated with the use of these crops could result in population declines of insectivorous bats (LopezHoffman et al 2014). …”

“…Extending these estimates to agricultural areas throughout the USA suggests that bat predation could have a value of nearly US $23 billion annually (Boyles et al 2011). These benefits hold for both conventional and transgenic cotton (Federico et al 2008), although the introduction of Bt cotton (a genetically modified organism whose tissues produce an insecticide derived from the bacterium Bacillus thuringiensis), coupled with reduced area in cotton cultivation, has led to a decline in the overall value of this pest limitation service (Lopez-Hoffman et al 2014). …”

Seasonal Change in the Diet Composition of the Asian Parti-Coloured BatVespertilio sinensis

“…Our study roost, which consisted of more than 1000 individuals every year, is located in a small patch of forest, which is surrounded by extensive agricultural fields. If this species uses these agricultural fields as a feeding habitat, their ecological function in the agricultural ecosystem might be as influential as has been shown for other insectivorous bat species (Cleveland et al 2006;Federico et al 2008;Williams-Guillén et al 2008). In this case the conservation and management of V. sinensis in the study area is important for economic reasons.…”