Libro de Resúmenes / Book of Abstracts (Español/English)

Resumenes 70
Modeling the agricultural pest control service provided by
brazilian free tailed bats (Tadarida brasiliensis) in Texas
The diet of Brazilian free-tailed bats (Tadarida brasiliensis) in
southern Texas during the summer includes significant proportions of major
crop pests in the area such as corn earworm or bollworm (Helicoverpa zea)
and fall armyworm (Spodoptera frugiperda). The significant natural
agricultural pest control service that these bats provide has both a direct
economic impact and an avoided costs component. We have developed a
mathematical model based on difference equations that describes bat and
bollworm population dynamics in conventional (without an insecticidal
protein incorporated) and Bt (with Bacillus thuringiensis protein
incorporated) cotton crops in southwestern Texas during the summer. The
model focuses on the direct ecological and economic impact of bats by
simulating scenarios such as changes in bat population numbers including
total absence of bats, different patterns of insect migration and pest control
strategies. Number and timing of insecticide applications, cotton yield and
number of insects emigrating from the cotton crops are used as main
response variables to analyze the direct economic impact of the bats. A
sensitivity analysis was performed to identify parameters of large effect.
Then simulations varying these parameters randomly within their possible
ranges were performed. Direct beneficial effects of bats on conventional
cotton production include situations where one, or sometimes two,
insecticide applications can be avoided; the first application can be delayed
by a period of a few days; the period between applications increases; the
emigration of adult moths out of the region is appreciably reduced; and the
number of bolls damaged by insects decreases significantly. The projected
savings to the conventional cotton producer over a growing season due to
bat consumption of pests is, on the average, US$83 per hectare. Given the
model assumptions, the bats impact the number of insecticide applications
needed in Bt cotton, reducing them by two. The average benefit of having
bats foraging above Bt cotton is approximately $40 per hectare. From an
economic perspective and at a local scale, bats have a positive effect on
both conventional and Bt cotton crops. At a broader scale, the avoided costs
may be quantified in terms of the consumption of adult moths by bats,
which significantly reduce the emigrating numbers of insects that would
infest crops in northern areas.