Location: Integrated Cropping Systems Research2012 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 FY12 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 rootworm matings have been completed. Lifetime egg production is still being collected. Video analysis is expected to begin soon. 1a2. Mate competition contests between resistant and susceptible western corn rootworm are partially complete, and eggs are being collected. 1b. We exposed western corn rootworm larvae to SmartStax and isoline seedlings with little success in obtaining survivors, likely because the corn had an insecticidal seed treatment. Experiments will be re-run using untreated seeds. We added a field component in which we are selecting for resistance to SmartStax and are now in our third year of selection. 2a. The corn/soybean breeder involved in selecting lines for host-plant resistance left for another position, leaving us a critical vacancy. 2b & c. The cover crop research was inhibited by a poor stand in two of the three cover crops under study. Cover crops were established in late summer, 2011. Corn was planted and infested in spring of 2012. Due to the poor stand in the cover crops, we decided to focus on how slender wheatgrass affects corn root structure and rootworm performance, and will establish the experiment in late summer 2012. The research on density dependent predation on corn rootworm immatures was completed in previous cycles ahead of schedule, and the manuscript is in preparation. 3a & b. Weed growth in soybean was reduced almost 90% with a systems approach to managing weeds. A 2-year system comprised of a small grain crop, a fall cover crop (oat + oilseed radish), and no-till, reduced biomass of the weed community in soybean 87% compared to a system of tillage and no cover crops. Suppression included both reduced seedling density and delay of seedling emergence. Fall mowing of red clover reduced its stand more than 75%; alfalfa tolerated fall mowing without stand loss. Alfalfa establishment was excellent following an oat/pea mixture harvested for forage, but not following spring wheat. Granivore populations were monitored throughout the latter half of the season in the soybean plots. A pilot study on the seed marking technique was used to identify dozens of seed predators. 4a. In FY2012, 445 domesticated and wild soybean lines were evaluated for aphid resistance. 4b. The goals of this project are being accomplished using amended methods from those presented in the original CRIS project. We are examining how specific components of a weed community associated with soybeans affect insect community dynamics. Replicated soybean plots were sampled weekly in 2011 and 2012 for soybean aphid densities per plant and for predator communities (using sweep nets). Preceding crop affected insect dynamics, although final analysis is pending.
1. Managing soybean aphids with pest-resistant plants may be tougher than we thought. 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. Overall, results of field and laboratory tests conducted by the USDA-ARS laboratory in Brookings, SD, coupled with previous reports of biotypes virulent to some resistant lines, suggest that deployment of soybean lines with a single aphid-resistance gene may have limited durability for soybean aphid management, and that deployment strategies relying on multiple resistance genes or diverse modes of resistance need to be tested as management strategies against soybean aphid.
2. Insecticide use in the Northern Great Plains is on the rise, but not always for good reason. Insecticides are often necessary to manage pest populations, but overuse can encourage pest resistance and result in unnecessary environmental and human health risks. Many field crop seeds planted in this region (e.g., corn, soybeans, wheat, canola, etc.) are currently treated with systemic insecticides as a preventative measure, regardless of whether pests are present in a field or not. A group of scientists at the USDA-ARS-NCARL and at South Dakota State University (both are in Brookings, SD) showed that insecticide use has increased in recent years, even on GM crops like Bt corn which are engineered to produce their own insecticidal toxins. A two-year survey of non-Bt cornfields on 53 farms in SD revealed that the major pests of corn (European corn borer and corn rootworms) were present at very low levels throughout the state, seldom if ever causing economic damage to the crop. This begs the question of why more insecticides are being applied to cornfields in SD and the surrounding region. In another experiment, scientists at this location evaluated the benefits and costs of insecticidal seed treatments in soybeans in a two-year, replicated field trial. This research showed that insecticidal seed treatments cost farmers money, but do not provide any control of soybean aphids (the dominant pest of soybeans in this region), nor did the insecticides improve soybean yields. Collectively, the data suggest that insecticides are applied to several main crops unnecessarily in many cases. Recommendations from the study should lead to a more prudent use of this expensive, but valuable producer tool.
3. Corn tolerance to weed interference varies with preceding crop. Crop diversity may improve tolerance to the negative competitive effects that weeds have on crops (called weed interference) and reduce the need for herbicides. An experiment by researchers at the USDA-ARS laboratory in Brookings, SD measured weed interference (green and yellow foxtail, for example) in corn as affected by the preceding crop in two studies. Corn was most tolerant to weed interference following dry pea; compared to soybean, dry pea improved corn tolerance more than two-fold. Corn also yielded the highest in weed-free conditions following dry pea; averaged across four years, corn yielded 13% more following dry pea than following either soybean or spring wheat. Crop diversity has helped producers reduce herbicide inputs in the Great Plains and may provide an additional benefit of reducing weed impacts on crop yield.
4. Disappearance of rare lady beetles: the shrinking beetle hypothesis. The nine-spotted lady beetle was historically one of the most common lady beetles across the US and southern Canada. In the 1980s it became extremely rare. In 2008 beetles were collected from field populations in Oregon and South Dakota. Initial observations by scientists at the USDA-ARS research laboratory in Brookings, SD suggested that these individuals seemed smaller than the average mean size of historical specimens. A series of experiments was therefore conducted to determine if there had been a significant decrease in beetle size and if any decrease found was due to a genetic change or to environmental factors. Field-collected beetles were 20% smaller than specimens bred in captivity or from collections. Laboratory tests suggested that environmental factors were prominent in the observed decline in beetle size. The results may be useful to conservation biologists in understanding how or why species become rare within the environment, and may give some inference on how rare species could be promoted within a habitat.
5. Insect predators get around in croplands. Farmers need uniform pest suppression throughout crop fields. Field edges and within-field patches of weeds or other vegetation are non-uniform, but are important sources of insect predators. To better understand how predators disperse throughout a farm field, entomologists at the USDA-ARS laboratory in Brookings, SD used novel marking and mapping techniques to measure insect predator mobility. Insect predators moved throughout the studied croplands to a much greater extent than previously believed. Data from the study will allow practical recommendations for the distance between non-crop vegetation and cropped areas that could increase control of pest insects by predators.
6. Female rootworms like the presents of big fellas. Female rootworms may choose to mate with males that provide them with the largest gift (called a spermatophore) during mating. In Bt cornfields, the non-Bt refuge delays the development of rootworm resistance to Bt technology, but an underlying assumption of this refuge strategy is that females like all males equally. Entomologists at the USDA-ARS research laboratory in Brookings, SD studied the size of spermatophores exchanged between male and female northern corn rootworms. The weight transferred during mating was directly related to male size and accounted for about 4.4% of his weight. Farmers using Bt corn varieties that kill corn rootworms have to include a non-Bt refuge, where rootworms can survive to mate with any rootworms that may be resistant to the nearby Bt corn. This work shows that northern corn rootworm beetles may mate preferentially with larger males. If the toxins from Bt corn make rootworms smaller (a common phenomenon), then females from the nearby non-Bt corn refuge may not be as interested in them. This work has important design implications for the size and distribution of non-Bt corn refuges planted by corn producers.Carr, P.M., Anderson, R.L., Lawley, Y.E., Miller, P.R., Zwinger, S.R. 2011. Organic zero-till in the northern Great Plains: opportunities and obstacles. Renewable Agriculture and Food Systems. 27:12-20.