Agriculture Reference
In-Depth Information
In the presence of a mobile pest, farmers might not account for the
effects of their pesticide use decisions on the evolution of resistance nor for
the effects on regional pest population dynamics (Miranowski and Carlson,
1986). Hueth and Regev (1974) suggest that the institution of a tax equal to
the marginal user cost could improve social welfare by ensuring that the
costs associated with resistance are incorporated by farmers. Regev et al.
(1983) examine such a tax in another theoretical analysis; however, noting
the difficulty of applying the tax in practice, they suggest pesticide-use
restrictions as an alternative.
1
For the purposes of this discussion, we are ignoring the costs associated with the
accumulation of toxic pesticide residues, leaching of pesticides into surface
and groundwater resources, and pesticide drift.
Refuge requirements depend on economic factors.
Hurley et al. (2001)
and Livingston et al. (2004) examine the characteristics of economically
efficient refuge requirements for U.S. corn and cotton producers, respectively,
for the single-toxin Bt corn and Bt cotton varieties. Both studies demonstrate
that economic returns might be improved over the long run if corn and cotton
producers comply with refuge requirements because of forestalling the onset
of Bt resistance. The size of the economically efficient refuge requirement,
however, was shown to depend on the length of the time horizon, the discount
rate, and resistance evolution to conventional insecticides used to control
target insect pests in the refuge acres. The refuge's ideal size was also shown
to be extremely sensitive to how dominant the inherited Bt resistance trait is.
Larger refuges are required to maintain susceptibility to Bt in target pest
populations for longer time periods and when Bt resistance is inherited as a
more dominant genetic trait by the target insect species. Livingston et al.
(2007) provide empirical support for the relaxation of mandatory refuge
requirements for farmers who plant cotton varieties that express multiple Bt
toxins in areas that have sufficient sources of unstructured refuge.
30
These
varieties control the target pest species much more effectively than single-
toxin varieties. Also, most U.S. cotton is grown in areas with sufficient sources
of unstructured refuge—including both cultivated and uncultivated crops and
plants that serve as alternative hosts for the target insect pest species,
particularly the cotton bollworm and the tobacco budworm—effectively
eliminating the need for a structured (or minimum) refuge requirement. Cotton
growers in Arizona, California, New Mexico, and west Texas are still required
to plant minimum, structured refuges.
