Location: Corn Insects and Crop Genetics Research
Project Number: 5030-22000-018-000-D
Project Type: In-House Appropriated
Start Date: Oct 1, 2015
End Date: Sep 30, 2020
Objective 1: Improve knowledge of the ecology, genetics, and behavior of key corn pests, especially corn rootworm and lepidopteran species, such as European corn borer, corn earworm and western bean cutworm, in relation to pest abundance and insect resistance to transgenic corn. Sub-objective 1.A. Correlate genetic markers with phenotypic traits of interest in European corn borer, western corn rootworm and western bean cutworm. Sub-objective 1.B. Determine how larval movement and adult dispersal influence insect resistance to transgenic corn. Objective 2: For corn agro-ecosystems, determine potential impacts of changing farming practices on the demographics and ecology of pest and non-pest arthropods, such as the monarch butterfly. Sub-objective 2.A. Assess the potential value of neonicotinoid insecticide seed treatments to growers of major row crops under different agronomic conditions. Sub-objective 2.B. Develop strategies for improving monarch butterfly habitat in modern farm landscapes. Objective 3: Characterize genetic and biochemical responses associated with corn defenses to rootworm and lepidopteran caterpillar pest injury to enhance conventional and transgenic crop protection strategies. Sub-objective 3.A. Develop genetic markers and genomic tools for western corn rootworm, European corn borer, western bean cutworm, and other pests of corn. Sub-objective 3.B. Characterize genetic regulation of surface lipids on corn silks and assess protective capacity of these lipids on corn earworm feeding.
Field-resistance in western corn rootworm (WCR) to Cry3Bb1 Bt toxins and in European corn borer (ECB) to Cry1Fa and Cry1Ab toxins will be mapped by using genotyping-by-sequencing (GBS) protocols and single nucleotide polymorphism (SNP) markers. Pedigrees will be constructed from Bt resistant and susceptible individuals of both species. GBS will be performed by constructing genomic DNA libraries from non-size-selected fragments, to which adapters with a unique barcode are ligated. A population mapping approach using a high density of SNP markers will be taken to identify loci that differ significantly between E- and Z-race ECB. The premise of population mapping is similar to quantitative trait loci (QTL) mapping, but SNPs with skewed frequencies between races are assumed to result from either selection for race-specific adaptations or genetic drift facilitated by restricted gene flow. GBS-derived SNP markers will be used to estimate gene flow among WCR populations. The strategy will be to estimate Wright's neighborhood area for WCR, the radius of which constitutes a measure of the typical distance genes move per generation. Dispersal and survival rates of fall armyworm (FAW) will be measured in field plot trials. FAW egg masses will be placed in the whorl of vegetative-stage corn plants surrounded by uninfested plants. Living and dead larvae on plants will be counted periodically using destructive sampling. Planting arrangements will include various combinations of Bt and non-Bt isoline plants. Flight behavior and capacity of WCR will be characterized and compared across three Cry3Bb1-resistant and two susceptible strains using flight mills to determine the degree to which resistance affects dispersal. In collaboration with other ARS laboratories and as a NP304 effort, a comprehensive review of the literature will be conducted to provide information on the usefulness of seed treatment with neonicotinoid insecticide in controlling target pests and protecting crops from yield loss. A series of studies will be conducted related to milkweed species selection (larval performance and oviposition preference), and milkweed plant establishment (determining patch sizes and maximizing sustainability of milkweeds). Initially, studies will focus on four Asclepias species found in Iowa: common milkweed, A. syriaca, swamp milkweed, A. incarnata, butterfly weed, A. tuberosa, and whorled milkweed, A. verticillata. Also, studies will be conducted to determine how to maintain these plants in the landscape while avoiding loss from plant competition. This will require identifying the best companion plants for the targeted milkweed species. Two sources of corn germplasm will be used to screen for silk activity against corn earworm (CEW). These corn lines and CEW resistant checks will be grown in the field. Emerged silks will be harvested, immediately frozen in liquid nitrogen, lyophilized, and ground to a powder using a knife mill. One cohort of powdered silks will be used for surface lipid metabolic analysis, while another will be used for CEW bioassays, allowing the metabolomic analysis and CEW feeding studies to be conducted in parallel.