Understanding successful resistance management: The European corn borer and Bt corn in the United States

The European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) has been a major pest of corn and other crops in North America since its accidental introduction nearly a hundred years ago. Wide adoption of transgenic corn hybrids that express toxins from Bacillus thuringiensis, referred to as Bt corn, has suppressed corn borer populations and reduced the pest status of this insect in parts of the Corn Belt. Continued suppression of this pest, however, will depend on managing potential resistance to Bt corn, currently through the high-dose refuge (HDR) strategy. In this review, we describe what has been learned with regard to O. nubilalis resistance to Bt toxins either through laboratory selection experiments or isolation of resistance from field populations. We also describe the essential components of the HDR strategy as they relate to O. nubilalis biology and ecology. Additionally, recent developments in insect resistance management (IRM) specific to O. nubilalis that may affect the continued sustainability of this technology are considered

Southern Corn Rootworm (Coleoptera: Chrysomelidae) Adult Emergence and Population Growth Assessment After Selection With Vacuolar ATPase-A double-stranded RNA Over Multiple Generations

The southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), was exposed over multiple generations to vacuolar (v)ATPase-A double-stranded (ds)RNA, first as adults and later, as neonate larvae. During adult selection, high mortality and lower fecundity were observed in the RNAi-selected cages after beetles were exposed to sublethal dsRNA concentrations that varied between LC40 and LC75. During larval selection, a delay in adult emergence and effects on population growth parameters were observed after neonates were exposed to sublethal dsRNA concentrations that varied between LC50 and LC70. Some of the parameters measured for adult emergence such as time to reach maximum linear adult emergence, time elapsed before attaining linear emergence, termination point of the linear emergence, and total days of linear emergence increase, were significantly different between RNAi-selected and control colonies for at least one generation. Significant differences were also observed in population growth parameters such as growth rate, net reproductive rate, doubling time, and generation time. After seven generations of selection, there was no indication that resistance evolved. The sublethal effects caused by exposures of southern corn rootworm to dsRNAs can affect important life history traits and fitness especially through delays in adult emergence and reduction in population growth. Although changes in susceptibility did not occur, the observation of sublethal effects suggests important responses to potential selection pressure. Assuming resistance involves a recessive trait, random mating between susceptible and resistant individuals is an important factor that allows sustainable use of transgenic plants, and delays in adult emergence observed in our studies could potentially compromise this assumption

Linkage of an ABCC transporter to a single QTL that controls Ostrinia nubilalis larval resistance to the Bacillus thuringiensis Cry1Fa toxin

AbstractField evolved resistance of insect populations to Bacillus thuringiensis (Bt) crystalline (Cry) toxins expressed by crop plants has resulted in reduced control of insect feeding damage to field crops, and threatens the sustainability of Bt transgenic technologies. A single quantitative trait locus (QTL) that determines resistance in Ostrinia nubilalis larvae capable of surviving on reproductive stage transgenic corn that express the Bt Cry1Fa toxin was previously mapped to linkage group 12 (LG12) in a backcross pedigree. Fine mapping with high-throughput single nucleotide polymorphism (SNP) anchor markers, a candidate ABC transporter (abcc2) marker, and de novo mutations predicted from a genotyping-by-sequencing (GBS) data redefined a 268.8 cM LG12. The single QTL on LG12 spanned an approximate 46.1 cM region, in which marker 02302.286 and abcc2 were ≤2.81 cM, and the GBS marker 697 was an estimated 1.89 cM distant from the causal genetic factor. This positional mapping data showed that an O. nubilalis genome region encoding an abcc2 transporter is in proximity to a single QTL involved in the inheritance of Cry1F resistance, and will assist in the future identification the mutation(s) involved with this phenotype

Coordinated \u3ci\u3eDiabrotica\u3c/i\u3e Genetics Research: Accelerating Progress on an Urgent Insect Pest Problem

Diabrotica spp. (western, northern, and Mexican corn rootworms) represent the main pest complex of continuous field corn, Zea mays (L.), in North America. The western corn rootworm, Diabrotica virgifera virgifera LeConte, also has become the main pest of continuous corn in Central and Southeastern Europe since its introduction near Belgrade 15–20 years ago, and it represents a major risk to Western Europe. It has already caused economic losses in Eastern Europe, and Western countries such as France have committed large expenditures for containment and/or eradication. Rootworm larvae feed on corn roots, and damaged plants are more susceptible to drought and disease, have decreased yield, and are prone to lodging. A recent economic analysis estimates that costs of control and yield loss are about $1.17 billion a year in the United States. Crop rotation and chemical control have been the primary management strategies, but the western corn rootworm is becoming increasingly difficult to control because of its sequential ability to evolve resistance to almost all management strategies that have been used. The recent deployment of transgenic Bt corn in the United States for controlling Diabrotica pests has raised concerns that rootworms will develop resistance to this technology as well, unless appropriate resistance management strategies are developed and practiced

Coordinated \u3ci\u3eDiabrotica\u3c/i\u3e Genetics Research: Accelerating Progress on an Urgent Insect Pest Problem

Diabrotica spp. (western, northern, and Mexican corn rootworms) represent the main pest complex of continuous field corn, Zea mays (L.), in North America. The western corn rootworm, Diabrotica virgifera virgifera LeConte, also has become the main pest of continuous corn in Central and Southeastern Europe since its introduction near Belgrade 15–20 years ago, and it represents a major risk to Western Europe. It has already caused economic losses in Eastern Europe, and Western countries such as France have committed large expenditures for containment and/or eradication. Rootworm larvae feed on corn roots, and damaged plants are more susceptible to drought and disease, have decreased yield, and are prone to lodging. A recent economic analysis estimates that costs of control and yield loss are about $1.17 billion a year in the United States. Crop rotation and chemical control have been the primary management strategies, but the western corn rootworm is becoming increasingly difficult to control because of its sequential ability to evolve resistance to almost all management strategies that have been used. The recent deployment of transgenic Bt corn in the United States for controlling Diabrotica pests has raised concerns that rootworms will develop resistance to this technology as well, unless appropriate resistance management strategies are developed and practiced