Development of Genetic, Chemical and Population-Based Tactics to Manage Key Kansas Soybean Insect Pests
Sustainable Production
Biotic stressCrop protectionField management Pest
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
C Michael Smith, Kansas State University
Co-Principal Investigators:
Brian McCornack, Kansas State University
William Schapaugh, Kansas State University
Jeff Whitworth, Kansas State University
+2 More
Project Code:
Contributing Organization (Checkoff):
Institution Funded:
Brief Project Summary:

Damage severity of the soybean stem borer has in Kansas counties but management strategies remain limited. RNAi gene silencing in soybean stem borer larvae is a new viable way to create borer-resistant plants, and promising results of previous experiments suggest this may be possible. Results demonstrate that adult colonization patterns vary between fields and through time and need to be better predicted. Objectives of this project include creating soybeans resistant by inserting borer RNA into the plants to interfere with genes necessary for borer survival; and improve insecticide efficacy by using host plant and other environmental conditions to adjust application timing and placement.

Key Benefactors:
famers, entomologists, applicators, ag retailers, extension specialists

Information And Results
Project Deliverables

Procedures for Objective 1:
1) verify gene silencing by RNAi in soybean stem borer larvae by silencing Lac2, a gene required for borer skin.
2) determine if silenced Lac2 or other beetle membrane proteins can be moved to soybean plants and expressed at levels sufficient to kill stem borer larvae and/or adult beetles.

Progress on Sub-objective 1 by Lina Aguirre, the PhD student conducting this research, has included developing a laboratory stem borer colony for experiments to test the effects of silencing Lac2; isolating stem borer Lac2; injecting larvae with silenced Lac2; and assessing changes in larvae and adults emerging from larvae. In a Sub-objective 1 replicated study just completed, 95% of stem borer larvae injected with RNAi silenced Lac2 died as larvae or beetles. A few treated larvae have become adults, and those have atrophied wings, un-tanned cuticle, curled antennae, do not feed and have died. Additional replicated experiments will be conducted with RNAi injected larvae to verify results of the first study.

Sub-objective 2 experiments will be conducted in FYI9.
Procedures for Objective 2:
1) incorporate key factors influencing adult pest distribution patterns into treatment placement decisions for stem borer and other important soybean pests,
2) devise and update spray recommendations to optimize efficacy of newer chemistries that target soybean stem borer, stink bugs, and soybean podworm and
3) determine the economic value of reducing insecticide coverage at mitigating losses by key pests in Kansas soybean.

Due to year-to-year and field-to-field variability in pest abundance and community composition, we propose repeating experiments in several locations over the next 2 years of this project. This is especially important when management recommendations will be direct outcomes from this work. We will continue to use several geostatistical techniques to model the spatial distributions of key pests through time and compare infestation patterns with targeted insecticide treatments, either as border treatments or large-scale insecticide trails. We will continue to test the appropriateness of site-specific strategies (i.e., spraying on the field edges) not only for soybean stem borer but for other economically important soybean pests as well. We will continue to examine the use of site-specific management practices by conducting large-scale field studies that aim to quantify adult pest movement into and around soybean fields at risk of infestation. Field-collected samples of soybean pests will be obtained using sweep nets samples from each waypoint (n > 40 per field, 10 to 15 commercial fields). Samplers will navigate to predetermined waypoints and a 20-sweep sample will be taken in each of the cardinal directions. Adults from each 20-sweep set will be bagged and identified in the lab. To relate timing of infestation by key pests and product efficacy (i.e., reduced plant damage, lodging etc.), we will use field-level vegetation maps collected from small unmanned aerial systems (sUAS); funds for aerial imaging are being leveraged from an existing, international grant (McCornack, lead PI).

Evaluating the efficacy of candidate insecticides for pest insect control will continue, based on production needs, loss in severity by key soybean pests and industry interest (see Accomplishments below). In addition, we will expand this sub-objective to explore effective product carrier volumes, appropriate nozzle types, and other potential factors affecting insecticide penetration or distribution into the soybean canopy, especially during late-season infestations. This research is imperative to reliable use of newer insecticide chemistries. We have accepted a graduate student for this project to begin in January 2017 whose primary focus will be to model the value of site-specific management strategies in general and ways to optimize insecticide applications for controlling key pests in soybean.

Procedures for Objective 3.
Efforts will continue to develop text-based discussions, maps, tables, and graphs posted to the KSRE Soybean Insect Management Guide (http://www.ksre.ksu.edu/bookstore/pubs/Mf743.pdf).
Work is in progress to update the insect pest management information section for the Kansas Soybean Management 2017 publication (https://www.bookstore.ksre.ksu.edu/pubs/MF3154.pdf). Co-PI Whitworth and Dr. Holly Schwarting wrote the insect pest chapter for the just-completed publication: Ciampitti et al. 2016. Soybean Production Handbook. (KSRE #C449) (http://www.bookstore.ksre.ksu.edu/pubs/c449.pdf). All new information will also be inserted in our soybean pest management web-based decision support systems like myFields.info (http://myfields.info/pests/dectes-stem-borer), and discussed during field days, radio programs, newsletters, and via other educational opportunities as appropriate. For a list of all soybean pests and associated management guides on myFields.info, visit http://myfields.info/pests. The support of the Kansas Soybean Commission will continue to be highlighted in all of these endeavors.

Final Project Results

Accomplishments since last report

Objective 1: Create soybean plants resistant to soybean stem borer by inserting borer RNA into soybean plants to interfere (RNAi) with genes necessary for borer survival.
Lina Aguirre, the PhD student conducting this sub-objective, established a replicated 2017 field cage experiment of sunflower, ragweed and soybean plants infested with soybean stem borer adults. Larvae collected from plants displayed major differences in the types of genes they express in response to feeding on the three plants. Results to date indicate that larvae fed soybean turn on more than 80 genes not expressed by larvae feeding on sunflower. Of these genes, many are involved in destroying or neutralizing ingested substances in the larval gut. The ability of larvae fed soybean to upregulate the expression of these genes may enable larvae to use soybean as a host. This information will be used to identify candidate genes that can be efficiently silenced to kill borer larvae.

Objective 2: Improve insecticide efficacy by using host plant developmental stages and other environmental cues or conditions to adjust timing of application.
Cooperators were identified early in the growing season twelve commercial production fields and cooperators identified in Clay and Washington Counties were used to survey soybean for defoliators (e.g., loopers), pod (e.g., Helicoverpa zea or soybean podworm) and stem feeders (Dectes texanus). Fields range in size (55-200 acres), variety, and production practices (irrigated vs. dryland, row spacing, plant population, etc.). The survey started shortly after plants emerged (V3-4) and finished in the late reproductive stages (R6-7); fields were located across a north to south gradient and covered several counties in Kansas. Fields were sampled weekly using sweep nets (30 locations per field) in the perimeter and interior portions of each field. All stink bug specimens were sent to the University of Minnesota as part of a North Central Soybean Research Program project, which aims to develop sampling plans for stink bugs in soybean using data from across the North Central US. In addition, these data are being used to study how landscape or land use around these fields impacts stink bug populations and/or abundance. All other pest species data collected from Kansas soybean are currenlty being used to model the utility of site-specific management strategies (i.e., interior versus perimeter insecticide treatments). In addition, these data add to our sample database and are being used to develop sampling plans for several of the species observed; these models are still under development.

In three of these fields we initiated a small-scale (approx. 2 acres) study focused on evaluating the effectiveness of newer insecticide chemistries at different carrier volumes; only one field had treatable levels of defoliators and insect feeders, so it was used to evaluate interactions between carrier volumes and insecticide rates. Prior to insecticide treatments, we sampled plots using sweep nets (10 sweeps per plot per location) and individual specimens from the most abundant pests, which in this case green cloverworm and thistle caterpillar, were individually weighed. Plots were swept 6 days post application and individuals from the same two species were weighed. Carrier volumes tested were 10 and 20 gallons per acre (GPA) and Prevathon and Steward were the two insecticides applied. We also harvested a 1.5 m section of row from each plot and are currently evaluating individual pods by node for damage. There were no significant differences between treatments when comparing pest weights per 10 sweeps prior to the application of insecticides for either green cloverworm (F = 1.32; df = 8,62; P = 0.249) or thistle caterpillar (F = 0.74; df = 8,62; P = 0.636). This was expected and this location provided a uniform infestation to test for effects of application rate at varied carrier volumes. Post application weights of these two pests were significantly different. For example, green cloverworm (F = 6.83; df = 8,57; P < 0.0001) decreased 120-fold in treated plots compared to the untreated control; however, there were no significant differences between treatments. There are several factors that could attribute to this non-result, one of which is drift between plots. We are currently exploring vegetation data maps from these plots, both from satellite sensors and those deployed on small unmanned aircrafts (sUAS). In general, these data will be used to evaluate the level and location of protection these products provide against seed-feeding insects. We plan to further explore these data to correlate changes in plant biomass with changes in herbivore biomass and any impacts on soybean yield. The primary objective of this first year was to ensure a suitable experimental design (e.g., plot spacing, minimized drift, etc.). A similar experiment is planned for the 2018 field season but for multiple locations; county agents have been identified and a list of collaborating growers is currently being drafted.

Objective 3: Expand web pages and other educational materials associated with soybean insect pests.
Co-PI Whitworth and Dr. Holly Schwarting established foliar insecticide trials to test new products and differing rates of application for registered products against green cloverworm, thistle caterpillar and bean leaf beetles. The efficacy of 12 new-chemistry seed treatments for bean leaf beetle control were also tested. Efficacy results and resultant yields are still being determined for these trials. Results of all trials will be posted to the KSU Extension Entomology website and made available to all stakeholders via the KSU entomology website to help Extension personnel and others make the most judicious recommendations relative to pest control and integrated pest management. Insecticide products and links to labels were added to the Chemical Selection tool (https://www.myfields.info/chemical/selector/search) on myFields.info web-based platform. Users can select a crop, time of year, and easily find product labels for registered products. Other features that may be of interest can be found at: https://www.myfields.info/features.

View uploaded report Word file

A major accomplishment occurred toward the goal of creating soybean stem borer-resistant soybean plants. Genes specifically used by borer larvae as they feed in the soybean plant stem were identified. Experiments are in progress using some of these genes, which have silenced (turned off) and inserted into modified soybean plants to determine if larvae die when feeding on these modified plants. Statewide sampling was conducted in 2017 for presence of soybean for defoliators, pod feeders or stem feeders, to study how landscape or land use around crop fields impacts pest populations and/or abundance. Efficacy results and resultant yields from 2017 foliar insecticide trials are posted on the KSU Extension Entomology website (https://www.myfields.info/chemical/selector/search) on myFields.info web-based platform.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.