Rethinking refuge: Another look at existing IRM paradigms and emerging options for new Bt PIPs

Since the first Bt corn and Bt cotton Plant Incorporated Protectants (PIPs) were registered, both agricultural biotechnology and our understanding of Insect Resistance Management (IRM) have evolved. Much more is known about the biology, ecology, and behavior of corn and cotton pests today, and newly-developed (pyramided) Bt PIPs express multiple toxins with different modes of action against major target pests. In light of these developments, EPA is evaluating new refuge options and is revisiting the existing ‘structured refuge’ paradigm, which has been in place for over a decade. Several new strategies have been proposed by PIP registrants, including natural refuge for Bt cotton, reduced refuge for lepidopteran-protected Bt corn, and seed mix refuge for corn rootworm-protected Bt corn. Natural refuge, which involves the use of alternate plant hosts (weeds, wild hosts, and other cultivated crops) to produce susceptible insects, was approved by EPA for Bollgard II® and WideStrike® cotton in 2007 for adoption by growers starting in 2008. The other proposals for Bt corn are currently under consideration by the Agency. Industry must be able to provide convincing scientific evidence that these refuge options will not jeopardize the durability of new as well as existing PIP products and increase the risk of resistance evolution. In particular, EPA will examine the effects of host plants (i.e. Bt and non-Bt) on pest biology, ecology, and behavior, effects of expressed toxins (i.e. dose) on pest survival, potential for cross-resistance, and simulation models to evaluate the evolution of resistance.