Location: Integrated Cropping Systems Research2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Determine the biological, ecological, and behavioral basis that underlie insect pest (e.g, corn rootworm) resistance to management tactics (including GM crops), and develop novel crop and pest management technologies that enhance development of insect resistance management (IRM) plans. • Sub-objective 1a. In relation to IRM, determine whether resistance to Cry3Bb1 affects the mating behavior and reproductive biology of western corn rootworm. • Sub-objective 1b. Develop rootworm strains resistant to additional Bt corn events and assess trajectory of resistance development and its implications for rootworm fitness. Objective 2: Develop non-chemical tools (e.g., host-plant resistance and biological control) for managing corn rootworms and other insect pests, and devise effective approaches to integrate them into corn production systems. • Sub-objective 2a. Advance germplasm with resistance to corn rootworm larval feeding. • Sub-objective 2b. Identify Quantitative Trait Loci (QTL) associated with reduced damage in rootworm-resistant corn lines. • Sub-objective 2c. Assess the feasibility of winter cover crops as a method for increasing biological control of corn rootworms. Objective 3: Develop strategies to integrate non-chemical weed population management into crop rotation systems and identify environmental and physiological factors that limit the effectiveness of key granivores to regulate weed populations. • Sub-objective 3a. Develop a rotation design that reduces weed community density in organic croplands. • Sub-objective 3b. Evaluate contributions of cultural practices and granivory to weed seedling emergence in soybeans. Objective 4: Examine how herbicide tolerant and insect resistant crop varieties affect multitrophic relationships among soybeans (and other crops), insect pests, and natural enemies. • Sub-objective 4a. Identify and characterize soybean germplasm that is resistant to the soybean aphid. • Sub-objective 4b. Determine the implications of glyphosate-tolerant soybeans on biodiversity and its contributions to biological control of soybean aphids.
1b. Approach (from AD-416)
Sustainable pest management ultimately involves applying ecological principles for reducing insect and weed pressure on key crops. Our project couples bottom-up and top-down processes to reduce key pests (corn rootworms, soybean aphids, and weed communities) of Northern Great Plains crops in agronomically feasible ways that mimic those that regulate pest species within natural habitats. In corn, we will identify lines with natural resistance to rootworms, and will find quantitative trait loci to facilitate their use by seed companies. We also will incorporate winter cover crops into corn production systems in ways that encourage endemic predator communities and increase their impact on rootworms. Fitness-related traits that influence the evolution of rootworm resistance to Bt corn will be identified, and this information will be incorporated into insect resistance management decision-making tools in order to preserve this pest management technology. In soybean, we will discover new soybean lines that express resistance to a key pest, the soybean aphid. Simultaneously, we will determine how to manage non-crop vegetation within soybean fields to promote aphid natural enemies. Weeds are well adapted to current crop rotations, and our research will optimize crop rotations using population-centered approaches that break the weed cycle and increase the impact of insect granivores on weed seedbanks, especially within organic systems. The simultaneous development of top-down and bottom-up mechanisms for pest management are incorporated into sustainable and integrated pest management systems to provide producers with profitable pest management solutions that can be realistically implemented on their farms.
3. Progress Report
Specific research conducted in FY11 advanced research on the use of bottom-up and top-down processes to reduce key pests (corn rootworms, soybean aphids, and weed communities) of Northern Great Plains crops in agronomically feasible ways that mimic those that regulate pest species within natural habitats. 1a. Substantial progress was made on arranging the rootworm matings and recording the precopulatory and copulatory behaviors. Fecundity data is being gathered on the females, and additional replicates are underway. 1b. Efforts have been made to optimize the assay procedure. Due to an insecticidal seed treatment on the Smartstax corn seedlings, alternative methods have had to be developed before the Cry3Bb1 resistant and susceptible rootworms can be challenged by these seedlings. 2a. A critical vacancy (the corn/soybean breeder involved in selecting lines for host-plant resistance left for another position) stopped research on rootworm-resistant corn lines, and slowed research on soybean aphid-resistant soybean germplasm. 2b. The experiments on density-dependent predation on corn rootworm larvae were fully completed. A slender wheatgrass cover crop was established, and rootworm eggs were infested into the subsequent corn crop. Rootworm larvae were monitored weekly, and pest emergence and damage to the roots were recorded. Natural enemy populations were collected, returned to the laboratory, and their stomachs were analyzed for rootworm-specific DNA sequences. 3a & b. Fall weed growth after winter wheat harvest was suppressed by combining a cover crop combination of oilseed radish and oat with no-till. Weed density was reduced more than 95% compared to the conventional practice of tillage and no cover crops. Weed biomass was affected similarly by treatments. The high quantity of oilseed radish + oat biomass suppressed weed seedling survival. Red clover and alfalfa were successfully established at the first site, achieving densities greater than 100 plants/m2 for each species. Weed seed dishes were created and placed in the soybean treatments, and granivore communities associated with seed removal were collected and identified. A pilot study was conducted where seeds were marked with Rabbit IgG protein, and placed in the field. Seed predators were collected and their guts were analyzed using ELISA. Approximately 10-20% of the insects collected had consumed the marked seeds, indicating that this approach will be successful in future work. 4a. Aphid populations were assessed on 144 soybean lines in the greenhouse and 350 lines under field conditions, and relative aphid resistance levels were estimated. 4b. We examined the effects of weed densities on soybean aphid populations and natural enemies. Initial results indicate that soybean aphids are significantly less abundant in the soybeans with weeds, and aphids had breached economic thresholds by July 15 in the weed-free plots.
1. New insights on the biology of invasive insects. Exotic, invasive insects are a constant threat to agriculture and the national security of the US and worldwide. An ARS scientist at the North Central Agricultural Research Laboratory in Brookings, South Dakota, is determining some of the genetic and behavioral characteristics that allow invasive insects to spread across regions and worldwide. Together with researchers at the French National Institute for Agricultural Research, they made collections of the multicolored-Asian lady beetle throughout the US and world. This invasive insect negatively affects fruit and wine producers and homeowners around the world. Genetic analysis revealed little genetic diversity in the initial N. American population. Normally this lack of genetic diversity would constrain further invasion; however, the Asian lady beetles from N. America have become particularly invasive and have spread worldwide. Identifying the genetic characteristics that allow these insects to survive restrictions in genetic diversity should help regulators and scientists proactively identify species that have or may become invasive and implement control measures.
2. Crop rotations manage weeds in organic farming. Weeds are a major obstacle to successful crop production in organic farming. Producers may be able to reduce inputs for weed management by designing crop rotations that disrupt life cycles of weeds. Incorporating reduced tillage, diversifying crop rotations, and using winter crops in conventional farming operations have reduced herbicide use by 50% because weed density declines over time. An ARS scientist at the North Central Agricultural Research Laboratory in Brookings, South Dakota, devised a long-term crop rotation system comprised of perennial forages and annual crops that disrupt weed population growth and reduce weed density for organic farmers. This research provides a benchmark for designing crop rotations that benefit organic farmers and consumers by reducing herbicide inputs, fuel use, and production costs.
3. Mating frequency in corn rootworm affects resistance to genetically modified corn. Many pests of corn and cotton are managed with genetically modified crops that express the insecticidal protein, Bt. In 2011, 65% of corn and 73% of cotton grown in the U.S. expressed Bt. An important pest of corn, female corn rootworms are believed to mate only once in their lifetime. If they mate more frequently, the risk of corn rootworm resistance to Bt corn increases because females have an increased chance of mating with a Bt-resistant male beetle. ARS scientists at the North Central Agricultural Research Laboratory in Brookings, SD, showed that many female corn rootworms will mate up to three times over their life. More frequent mating of Bt resistant females, particularly with resistant males, produce many offspring that survive Bt corn exposure, mate, and reduce the effectiveness of Bt corn. This outcome would reduce the value of Bt technology and indicates that seed companies and regulatory agencies should optimize measures that reduce the risk of developing Bt resistant insect populations.
4. Grass hosts of cereal aphids between wheat-cropping cycles identified. Several grasses serve as alternative hosts for cereal aphids—pests of wheat and similar crops—during the interval between summer harvest and fall-seeding in the Northern Great Plains. Grasses were sampled for cereal aphids by entomologists after wheat harvest at the North Central Agricultural Research Laboratory in Brookings, South Dakota, over three years. Eighty-five of 240 site samples had one or more kinds of cereal aphids, including 61 of 65 corn sites and 12 of 13 sorghum and sudangrass sites. All high ratings of aphids occurred on field corn, and low frequencies of cereal aphids were found on volunteer small-grains and weedy grass species. Recent trends of expanding corn acreage in the Great Plains may potentially lead to concomitant increases of cereal aphids and intensify the risk to producers of fall infestation of winter grains by cereal aphids.
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