Project : USDA ARS

ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Research Project #439118

Research Project: Productive Cropping Systems Based on Ecological Principles of Pest Management

Location: Integrated Cropping Systems Research

2021 Annual Report

Accomplishments
1. Managing soybean aphid with a resistant cultivar is highly effective and precludes the downsides of insecticides. The soybean aphid remains an important pest of soybean in the Midwestern U.S. and southern Canada. The predominant management strategy includes a combination of planting soybean seed treated prophylactically with insecticide and applying a late-season foliar insecticide. However, this strategy increases production costs, selects for insecticide-resistant aphids, and escalates the chances of detrimental side effects from insecticides. ARS scientists in Brookings, South Dakota, conducted a three-year field study from 2015 thru 2017 that evaluated insecticide seed treatment, foliar insecticide spray, and use of an aphid-resistant soybean cultivar containing aphid-resistance genes. Each of these three management tactics independently reduced soybean aphid population densities. By far, the resistant cultivar had the greatest impact on soybean aphid populations, reducing them by 28- to 150-fold per year, whereas insecticide seed treatment reduced aphid populations 1.7- to 3.5 fold per year, and foliar insecticide spray reduced it from 2.0- to 5.6-fold per year. The study’s results demonstrated the viability of a soybean cultivar with two aphid-resistance genes as an alternative to the common strategy of using insecticides to manage this pest.

2. Best to base management decisions about corn rootworms at the local level. The western corn rootworm is a significant pest of field corn across the United States Corn Belt. Farmers in Nebraska have seen greater than expected crop injury from western corn rootworm despite widespread use of transgenic corn hybrids that express a particular protein known as Cry3Bb1 to manage the pest. ARS scientists in Brookings, South Dakota, and in Nebraska determined that the pattern of crop injury is due to varying levels of resistance to Cry3Bb1 in rootworm populations among various Nebraska counties. Larval development metrics, including rate of development, head capsule width and fresh weight, were associated with western corn rootworm corrected survival on Cry3Bb1 corn. These metrics are important in understanding the ways that resistant rootworms adapt to Cry3bB1. Overall, the findings increase our insight of western corn rootworm population dynamics among field locations within the transgenic corn landscape and reinforce the importance of making corn rootworm management decisions based on information collected at the local level.

3. Wild soybean enhances the arsenal of aphid resistance genes. A particular type of wild soybean known as soja has many useful traits that can be bred into modern soybean cultivars, and these include insect resistance. A study by ARS researchers in Brookings, South Dakota, and Raleigh, North Carolina, evaluated 76 selected soja accessions and 14 soybean accessions for resistance against two virulent colonies of soybean aphid in experiment growth chambers. The two colonies included a new soybean aphid biotype known as ‘Accrue,’ which has a novel virulence pattern against known aphid-resistance genes, and another highly virulent biotype, known as ‘Volga16.’ Soja line PI 507624 showed strong resistance against the Accrue colony, whereas PI 597458 C showed strong resistance to Volga16. Based on results from these tests, follow-up studies are warranted to determine the genetic basis of aphid resistance in these two soja lines in order to inform breeding programs that are developing aphid-resistant soybean cultivars.

4. Feeding strategies of ants indicate higher biodiversity in particular bioenergy landscapes. A dominant trend in global land use has been increased acreage for bioenergy plants grown as an alternative to fossil fuels. This major shift in land use may impact how organisms that share these production lands obtain their nutrients and energy. Ants are ideal organisms for understanding how feeding strategies respond to changing land use patterns. Researchers in Brookings, South Dakota, and Michigan conducted long-term and large-scale experiments on plantings of corn, switchgrass, and restored prairie to understand how ants’ nutritional requirements and the availability of food resources interacted to shape their feeding strategies within each habitat. Ants responded by altering their feeding on plants vs. feeding on insect prey. In corn and switchgrass monocultures, ants became top predators, whereas in restored prairie they consumed a mix of animal prey and plant-based resources and thus increased the complexity of their associated food webs. The extended food webs of ants within restored prairie showed that this land use supports a broader mix of biodiversity than corn or switchgrass monoculture while providing a viable resource of bioenergy plants.

5. Behavior of the herbicide bicyclopyrone in soil is highly variable. Bicyclopyrone is an herbicide that is marketed for the control of herbicide-resistant weeds. However, there is a lack of extensive data on its interactions with soil that determine its weed-control efficacy and tendency to contaminate soil and water resources. Researchers at Brookings, South Dakota, in collaboration with scientists at St. Paul, Minnesota, and elsewhere, evaluated the behavior of bicyclopyrone in 25 different soils with a variety of properties. Retention of bicyclopyrone by soil varied by a factor of 70 and was not related to soil properties that are commonly observed to influence pesticide behavior, including soil organic carbon, cation exchange capacity, and clay content. Additional research is needed to better predict the conditions that present an increased risk of environmental contamination by bicylopyrone.

6. Imported gall midge thrives on invasive sow thistles in the Upper Midwest. Land managers must balance effective control of invasive weeds with minimizing the impact of large-scale herbicide sprays across range, pasture, and natural grasslands. As an alternative to herbicides, various insect species have been imported to North America and released for biological control of invasive weeds. A gall midge known as Cystiphora sonchi was released in Canada in the 1980s to control invasive sow thistles. ARS researchers in Brookings, South Dakota, and Washington, D.C., discovered the gall midge infesting sow thistles in Minnesota, North Dakota, and South Dakota in 2017 and 2018, and many of the sow thistles were heavily galled. The findings documented the gall midge’s establishment in the U.S., which represents a significant southward extension of its known geographic range. The instances of heavy galling suggest the gall midge’s potential to impact sow thistles at lower latitudes in North America. Further research is needed to determine the geographic extent of Cystiphora sonchi in the U.S., its impact on weeds, and the benefits to landowners.

7. Ant thermal traits predict the winners and losers under climate change. Current temperatures are predicted to increase with consequences for many organisms including insects, whose body temperature tracks the environment. From warm deserts to cold tundra, scientists at Brookings, South Dakota, and in Oklahoma documented how 33 ant communities across North America have changed over 20 years to test theoretical predictions that ants with higher thermal tolerance have increased at the expense of less thermally tolerant groups. Consistent with our predictions, we found a positive relationship between CTmax, the temperature at which muscle control is lost, and the proportion of sites in which an ant genus’ incidence had increased. However, this was not the case for CTmin, the low temperatures at which ants first become inactive. We suggest additional working hypotheses for why particular genera have increased, decreased, or remained constant through time and why mean annual temperatures and evolutionary history explained little of this pattern. We suggest that functional traits like CTmax are useful in predicting how ants will respond to rising temperatures and the impacts on their biodiversity.

U.S. DEPARTMENT OF AGRICULTURE

Integrated Cropping Systems Research: Brookings, SD