Seeds of Change: Corn Seed Mixtures for Resistance Management and Integrated Pest Management

Abstract

The use of mixtures of transgenic insecticidal seed and nontransgenic seed to provide an in-field refuge for susceptible insects in insect-resistance-management (IRM) plans has been considered for at least two decades. However, the U.S. Environmental Protection Agency has only recently authorized the practice. This commentary explores issues that regulators, industry, and other stakeholders should consider as the use of biotechnology increases and seed mixtures are implemented as a major tactic for IRM. We discuss how block refuges and seed mixtures in transgenic insecticidal corn, Zea mays L., production will influence integrated pest management (IPM) and the evolution of pest resistance. We conclude that seed mixtures will make pest monitoring more difficult and that seed mixtures may make IRM riskier because of larval behavior and greater adoption of insecticidal corn. Conversely, block refuges present a different suite of risks because of adult pest behavior and the lower compliance with IRM rules expected from farmers. It is likely that secondary pests not targeted by the insecticidal corn as well as natural enemies will respond differently to block refuges and seed mixtures. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. ABSTRACT The use of mixtures of transgenic insecticidal seed and nontransgenic seed to provide an in-Þeld refuge for susceptible insects in insect-resistance-management (IRM) plans has been considered for at least two decades. However, the U.S. Environmental Protection Agency has only recently authorized the practice. This commentary explores issues that regulators, industry, and other stakeholders should consider as the use of biotechnology increases and seed mixtures are implemented as a major tactic for IRM. We discuss how block refuges and seed mixtures in transgenic insecticidal corn, Zea mays L., production will inßuence integrated pest management (IPM) and the evolution of pest resistance. We conclude that seed mixtures will make pest monitoring more difÞcult and that seed mixtures may make IRM riskier because of larval behavior and greater adoption of insecticidal corn. Conversely, block refuges present a different suite of risks because of adult pest behavior and the lower compliance with IRM rules expected from farmers. It is likely that secondary pests not targeted by the insecticidal corn as well as natural enemies will respond differently to block refuges and seed mixtures. Seeds of

Role of dispersal in resistance evolution and spread

“…This may be related to the commercialization of rootworm-targeting transgenic corn expressing various insecticidal proteins derived from Bacillus thuringiensis (Bt). Growers tend to plant rootworm Bt corn even in rotated fields, either to protect against rotation resistant populations, or because elite high-yielding non-Bt hybrids are difficult to obtain [17]. This practice reduces the selective advantage to rotation resistant phenotypes in rotated fields, because mortality is as high as among susceptible phenotypes ovipositing in non-rotated Bt corn [18 ].…”

“…Larval dispersal between Bt and non-Bt plants can result in a sublethal dose, promoting differential survival of heterozygotes over homozygous susceptible larvae, thus accelerating accumulation of resistance alleles in the population. Models generally affirm that larval dispersal leads to faster evolution of resistance in a blended than in a block refuge system [17,50], unless substantial (but, unfortunately, realistic) grower noncompliance is included for the latter [51 ]. Recent research indicates that larval movement in several lepidopteran pest species is a threat to the blended refuge strategy [52][53][54].…”

Hybridizing transgenic Bt cotton with non-Bt cotton counters resistance in pink bollworm

“…Seed mixtures have several advantages relative to block refuges, particularly convenience for farmers and elimination of noncompliance with block refuge requirements (15,17). However, seed mixtures increase opportunities for larval movement between Bt and non-Bt plants or plant tissues, which could accelerate resistance evolution by raising the dominance of resistance or by reducing the survival of susceptible insects (13)(14)(15)17). Despite potentially profound implications of the seed mixture strategy for the sustainability of Bt crops, large-scale field tests of its efficacy have been lacking.…”

Analysis of resistance to Cry1Ac in field-collected pink bollworm,Pectinophora gossypiella(Lepidoptera:Gelechiidae), populations

“…This new refuge delivery concept for Bt cotton and is currently undergoing experimentation and appears to be a promising field-viable option. 26 …”