2012 Annual Report
1a.Objectives (from AD-416):
The objective of this seed grant proposal is to develop a two stage risk assessment tool. The outcome anticipated is a prototype risk assessment model that provides reliable forecasting capabilities for estimating the risk from a specific arthropod becoming established in corn production areas in South Dakota at the county level. The risk assessment will be based on county characteristics favorable to establishment of high consequence arthropods in a specific South Dakota county.
1b.Approach (from AD-416):
A two stage model is proposed. The first stage of the model will generate ordinal quantitative risk assessment estimates for arthropod establishment-risk based on county characteristics using a “scorecard qualitative assessment approach.” The second stage generates a probability estimate (a cardinal measure) for an arthropod of high economic consequence becoming established in a South Dakota county, based on the first stage risk assessment rankings. We intend to collect data on: a) county attributes associated with risk establishment, and b) county level arthropod infestation data based on standardized sampling procedures targeting seven herbivorous pests that represent different taxonomic and feeding guilds consistently problematic for conventional corn fields in South Dakota. The data will be used to calibrate the two-stage model.
The first stage of the two-stage model will be designed in accordance with the methodology developed in the country risk analysis literature. The country risk analysis methodology will be modified to provide qualitative risk rankings for county attributes correlated with successful pest establishment. The second stage will develop a logistic regression model that will relate the incidence of successful establishment in a county (sample data) to variables expected to influence the likelihood of successful establishment (county risk attributes).
Our proposed high consequence corn infesting arthropod risk assessment project overcomes two flaws identified in the non-indigenous species (NIS) risk assessment literature:.
1)our proposed county level risk assessment model provides cardinal rankings rather than ordinal rankings and thus provides a probability ranking for pest establishment risk; and.
2)our proposed model focuses on only the establishment stage of invasion at the county level.
In 2011, 25 field sites containing non-Bt corn (minimum 10 ac) with low levels or no insecticidal seed treatments were identified throughout the corn-producing region of eastern South Dakota. Sampling was targeted to occur within 2 weeks of corn tasselling. At each site, our crew of eight workers randomly harvested 50 plants. All arthropods on each plant were identified in the field and recorded. Data from all field sites were entered into a database, and numbers of pests and beneficial insects per plant were calculated.
The pests were categorized into caterpillar, aphids and rootworms. The caterpillar pests included western bean cutworm, european corn borer, and corn earworm. The corn rootworms included western, northern, and southern rootworms; aphids were primarily corn aphids. These pests never exceeded the economic threshold at any of the sites. European corn borer was the most consistent pest found, but a maximum of 10% of the plants were infested at a single site. A likely factor for this low level of pests may be the area-wide suppression of pests due to high adoption rates of genetically modified (GM) crops.
At all of the farms we sampled, we found a diverse community of beneficial insects (insect predators) including spiders, lacewings, pirate bugs, lady beetles, and syrphid flies. Densities ranged from 1 to 8 predators per plant. With 77,000 plants per acre, this translates to up to 660,000 beneficial insects per acre living just in the plant foliage. These predators are also working against pests, and should be preserved and encouraged through farm management practices as a free source of pest management for producers in the South Dakota.
In February 2012, an ARS Scientist from Brookings, South Dakota, went to the ARS lab at Sidney, Montana, with data from the corn survey in hand to work with the landscape ecologist there. The goal was to collaborate and uncover landscape metrics that correlated with the corn arthropod community, and with corn insect pests specifically. The manuscript is in preparation on this project.