Location: Integrated Cropping Systems Research2013 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 FY13 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. 1a1. All of the resistant and susceptible western corn rootworm matings for this study have been completed. All data on longevity, fecundity, and viable egg production is being analyzed with collaborators. A critical vacancy has delayed progress on this objective. 1a2. Almost all mate competition bouts have been established with Cry3Bb1 resistant and susceptible western corn rootworm males and females. Many of these events were recorded and we are collecting eggs from mated females. A critical vacancy has delayed progress on this objective. 1b. We have continued to expose western corn rootworm neonate larvae to SmartStax and a closely related non-transgenic hybrid and have seen some survivors. Because we could not get non-transgenic seeds without insecticidal seed treatment, we used another untreated variety as suggested by collaborator. We will continue exposing the larvae for several more generations and then begin looking for any fitness related costs associated with resistance. We also collected adults emerging from SmartStax corn as an added field component to selecting for resistance to SmartStax. We will continue to collect and rear corn rootworms emerging from the SmartStax field. 2a&b. The corn/soybean breeder involved in selecting lines for host-plant resistance left for another position, leaving a critical vacancy. 2c1. Because of difficulties in obtaining corn seed not treated with neonicotinoid insecticides, the focus of this project shifted slightly. We examined how increasing predator community structure in 16 corn fields (conducted over two seasons) affected predation intensity on corn rootworm immatures. The paper was submitted. 2c2. We examined how cover crops affect corn root structure, and established cover crops that will precede next year’s corn crop. 3a. Field trials in the 9-year rotation were established. Weed populations and crop characteristics and yield were recorded. Everything is moving forward according to plan. 3b. Field trials in the rotation were established. Ground dwelling insect communities were collected. Seed marking/gut analysis technology was validated and the manuscript published. Marked seeds were placed in the field and a test that detects the presence of the marker (ELISA) were conducted on field-collected predator stomachs. 4a. New soybean lines continue to be evaluated for soybean aphid resistant germplasm. A total of 350 soybean lines and 12 wild soybean lines were planted in field plots near Brookings in 2012 to screen for aphid resistance. However, aphid levels were very low in the plots, even despite supplemental infestation from colony-reared aphids, and meaningful evaluation of resistance was not possible. The 350 soybean lines and six of the 12 wild soybean lines were planted again in 2013 in field plots near Brookings. Natural infestations of soybean aphids were present in the plots a
1. A new strategy for deploying aphid-resistance genes in Soybean. The soybean aphid is a major, non-native pest of soybean that significantly reduces yield in northern production areas of North America. Insecticides are widely used to control soybean aphid outbreaks, but efforts are underway to develop host-plant resistance as an alternative management strategy. A review of field studies with soybean lines with aphid resistance, led by research entomologists with USDA-ARS in Brookings SD, suggests that deployment of soybean lines with a single aphid-resistance gene may have limited durability for aphid management, and that a strategy for optimal deployment of aphid-resistant genes in soybean is needed to ensure long-term use of this technology.
2. Predator diversity is key to reducing crop pests. Debate remains over whether predation on focal pests is enhanced by conserving a few strong predators versus entire predator communities with diverse species. Scientists with USDA-ARS in Brookings, SD measured predation on corn rootworm (the mostly costly pest of agriculture) in 16 corn fields whose predator community varied in its constituency, abundance and diversity. To establish the frequency of predation in these plots, they used genetic techniques to look inside the stomachs of predators for rootworm DNA. As predator abundance and diversity increased in a field, they more frequently consumed corn rootworms. The scientists suspect that this is because corn rootworms (and many other key pests) are defended from their predators, and predator abundance and diversity helps to drive them toward eating less tasty prey. This research confirms that predators are a significant source of non-chemical control for rootworms, and also supports the strategy that conserving diverse predator communities in cropland is important for reducing crop pests.
3. Sleepy northern corn rootworms beat crop rotation. Insects use diapauses to delay development or reproduction under unfavorable circumstances. Eggs of the northern corn rootworm (a significant pest of corn) are laid at the base of corn plants, overwinter in diapause, and hatch into corn the subsequent spring causing problems in cornfields that have not been rotated to soybeans. However, some rootworm populations adapted to this crop rotation by extending diapause for an extra year (these eggs overwinter twice), and bypassing the soybean phase of the rotation. This extended diapause trait has proliferated in recent years. In order to study the inheritance of diapause in rootworms, research entomologists at USDA-ARS in Brookings, SD mated beetles that diapause for 1 year with beetles that have extended diapause. Extended-diapause females invariably laid significantly more eggs with extended diapause relative to females that diapause for 1 year, regardless of the male’s diapause trait. This means that extended diapause is highly heritable and genetically dominant, which explains why northern corn rootworms have adapted to crop rotation in the region.
4. Identifying the cause of dry pea synergy to corn. Dry pea improves corn yield and tolerance to weed interference compared with soybean, spring wheat, or canola as preceding crops. To understand this synergy between dry pea and corn, scientists at USDA-ARS in Brookings, SD examined growth and nutrient concentration of corn following dry pea or soybean in sequence. They found that compared with soybean, dry pea improved corn tolerance to weed interference more than twofold. Biological factors affecting the soil likely underlie dry pea synergy with corn, as corn growth and development did not vary with preceding crop. Synergistic interactions will help producers reduce inputs such as fertilizers because corn is more efficient in using these resources when following dry pea compared to other crops.
5. New technologies for identifying weed seed predators. Granivorous insects are an important source of mortality for weeds in cropland, but clearly identifying which insects are most important as seed consumers remains elusive. Dandelion is a weed of no-till cropland and lawns worldwide. To identify seed predators, researchers at USDA-ARS in Brookings, SD marked dandelion seeds with a protein marker, and disseminated the marked seeds into five dandelion-infested habitats. They captured insects from the field, and analyzed their gut contents for the protein marker using an antibody assay (ELISA). At least 22% of insects had consumed dandelion seeds within the past 12 hours (approximately), with the top five most frequent consumers of seeds being pillbugs, millipedes, crickets, and a species of ground beetle. This work revealed a much more diverse seed predator community than has previously been described, and identified several taxa as granivores whose diet was previously poorly known. Using this technique will help scientists understand complex food webs and thereby facilitate developing and optimizing integrated weed management strategies for cropland.
6. New source of aphid resistance in early maturing soybean. Identification and genetic characterization of plant resistance to soybean aphid in early maturing soybean will facilitate development of aphid-resistant soybean lines for the northern production region. Among a total of 334 soybean lines tested in the greenhouse and field by researchers with USDA-ARS in Brookings, SD, PI 603712 was the only soybean line that consistently showed resistance to soybean aphid in all tests. Evidence suggests that PI 603712 may be a new source of resistance. In addition, relatively high levels of aphids on soybean lines previously assessed as resistant in South Dakota field tests suggest that particular races of soybean aphid, known as resistance-breaking types of aphids, may have been present in the field. This soybean germplasm can be used by breeders and seed companies to increase aphid resistance of soybean varieties, thereby minimizing the use of insecticides.
7. Successful continuous rearing of rare lady beetles. The nine-spotted ladybeetle and transverse lady beetle were historically two of the most common ladybeetles in agricultural fields across the US and southern Canada until their numbers declined drastically beginning in the 1980s. Scientists with USDA-ARS in Brookings, SD created a system for continuously rearing these two beetles in the laboratory. Techniques were developed to streamline egg deposition, maximize egg collection, and minimize cannibalism within rearing containers. This information can be used to aid conservation efforts and help determine the factors affecting their decline and possible recovery. This research will also be useful to the biological control agent producer industry, aiding them in optimizing production of beneficial insects.Bhusal, S.J., Jiang, G., Tilmon, K.J., Hesler, L.S. 2013. Identification of soybean aphid resistance in early maturing genotypes of soybean. Crop Science. 53:491-499.