Incorporating Native Plants in Insectary Strips to Promote Insect Diversity and Belowground Beneficial Microbes

Progress report for OS20-139

Project Type: On-Farm Research
Funds awarded in 2020: $20,000.00
Projected End Date: 03/31/2022
Grant Recipient: University of Texas Rio Grande Valley
Region: Southern
State: Texas
Principal Investigator:
Pushpa Soti
University of Texas Rio Grande Valley
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Project Information

Abstract:

Insectary strips, a habitat management strategy, that increases the functional agrobiodiversity of agroecosystems has been associated with reductions in the number of many herbivorous pests, in temperate, subtropical, and tropical cropping systems (Gurr et al., 2003; Swift and Anderson, 1994). Increasing the functional diversity of agroecosystems by combining crops with non-crop, secondary plant functional groups that provide resources for natural enemies and/or alter the behavior and distribution of pests has been a particularly effective approach to pest management (Wilby and Thomas, 2002) and gained interest among farmers. Hedge rows or insectary strips generally grown for other purposes can also serve as hotspots for soil organisms with the selection of proper species.

 

Goal of this project is to maintain permanent insectary strips or field margins which not only provide pest management service but also serve as wind breaks and refuge for soil organisms during the summer period where the field interiors are generally bare fallow. We propose diversifying the field margins with south Texas native plants to maintain and promote soil health along with insect pest management. With the increasing cost of managing insect pests, small scale organic growers in this region have shown an interest in maintaining insectary strips with native plant species which require minimum resources for maintenance, and played a important role in development of insectary strip pilot study in the Fall and Spring of  2019. The preliminary results have indicated the pest management benefits of insectary strips but the soil health benefits remains largely unexplored, which informed the experimental design of this proposed research along with the farmers willingness to add diverse groups of native plant species.

Project Objectives:

Experimental Design

We will establish a randomized block experimental design to test the multiple benefits of insectary strips at a certified organic vegetable farm, Terra Preta Farm, in Edinburg, Texas. During the fall planting season of 2020, 3 feet wide insectary strips will be created in between every 8 rows and these three treatments will be replicated 5 times in a 3-acre plot at the Terra Preta Farm, where the farmers grows a mix of onions and peppers. These strips will be maintained during the summer bare fallow period and again in the fall of 2021.

We will incorporate, native legumes and plant that highly mycorrhizal in the insectary strips and analyze the soil microbes: bacteria, fungi, nematodes, and mycorrhizal fungi communities along with the abundance and distribution of insect pests and natural enemies of the cash crop. This study will include three treatment composition insectary strips:

  • a cocktail of native plants including bundleflower, blue bonnet, and purple prairie clover Fabaceae); hooded windmill grass, pink pappusgrass, and shortspike windmill grass (Poaceae); Mexican hat, awnless bush sunflower, and orange zemenia (Asteraceae)
  • nonnative hedge row species commonly used, sunn hemp (Fabaceae)
  • control, no management

Data collection: Insects

Sticky traps, and pitfall traps will be installed in each of the treatment plots and will be collected biweekly. Insects collected from these traps will be grouped as herbivores, predators, parasitoids, and pollinators and analyzed to determine the insect diversity and beneficial pest ratio in the insectary strips compared to the control.

Cash crops

5 cash crops plants from each row be selected randomly to determine the proximity to the insectary strip and pest damage.  These plants will be evaluated biweekly when the plants start producing true leaves for insect damage and will be rated as high, medium and low pest damage. Total yield and marketable yield of the cash crops will also be monitored for each treatment.

Soil health

Rhizosphere soil samples and root samples of cash crops as well as hedgerow plants will be collected to analyze the microbial soil community and mycorrhizal colonization in the roots.

Roots and rhizosphere soil samples will be extracted from both the cash crop and hedgerows 2 times every season (early growing season and round harvest) to determine the nematode community and the prevalence of plant parasitic nematodes. We will also determine the total mycorrhizal fungi spore community assemblage and degree of mycorrhizal colonization in the roots of both cash crops and hedgerow plants.

The soil microbial community will also be analyzed following the FPLA extraction 2 times every season at the Soil Scientist in the Water Management Research Unit by Dr. Lauren Hale. Soil respiration will be measured biweekly with a 6400-09 Soil CO2 Flux Chamber during the study period.

Cooperators

Click linked name(s) to expand
  • Dr. Lauren Hale (Researcher)
  • Juan Raygoza - Producer

Research

Materials and methods:

We established a randomized block experimental design  to test the multiple benefits of insectary strips at a certified organic vegetable farm, in Edinburg, Texas. On October 2, 2020, 3 feet wide insectary strips were created between every 4 rows of cash crop that were made 5 feet wide from center to center. We transplanted 2 rows of broccoli 18” apart in a staggered manner on December 10, 2020. A total of 3 treatments of insectary strips were replicated 6 times on the 3,2670 square foot research plot. This three insectary strip treatments include:  

  1. Native wildflower mix, 19 species 
  2. Sunn hemp, a nonnative hedge row species commonly used 
  3. Control, no management 

Sunn hemp seeds were purchased from Johnny’s Selected Seeds Co. and the native wildflower cocktail was purchased from Douglas King Seeds in San Antonio, Texas. The seed mix, ‘Feed the Bees Pollinator Mix’, contains 18 species: Texas Bluebonnet, Cuero Purple Prairie Clover, Eldorado Engelmann Daisy, South Texas Gaillardia, Venado Awnless Bush Sunflower, Zapata Rio Grande Clammyweed, Partridge Peas, Plains Coreopsis, Purple Coneflower, Clasping Leaf Coneflower, Black-Eyed Susan, Mexican Hat, Lanceleaf Coreopsis, Lemon Mint, Standing Cypress, Drummond Phlox. 

Sunn hemp was planted at a recommended rate of 28 grams per square meter, and the native seed mix was planted at 10 grams per square meter.  Both Sunn hemp and the native wildflower mix were broadcasted by hand October 2nd, 2020. Seeds were slightly covered with soil and padded down with a garden hoe. Drip irrigation was applied once a week for 4 hours during the study periodSunn hemp will be replanted in June or July before planting onion for the next round of cash crop. These strips will be maintained during the summer and again in the fall of 2021. 

Insect community dynamics 

To determine if the native wildflower mix attracts more biodiversity compared to Sunn hemp and control, I collected insect samples 4 different times: before cash crop planting, during cash crop establishment, before cash crop harvest, and after cash crop harvest. I set up sticky traps and pitfall traps in three different locations: in the middle of the second cash crop row to the north of the insectary strips, on the edge of the insectary strips, and in the middle of the insectary strips (n=54) (Figure 3). Pollinator traps were installed at the middle of each insectary strips (n=18). The pitfall trap was prepared in 250 ml clear plastic cups filled with 60 ml of water and micro-90 solution. The pollinator traps were also filled with the water micro-90 solutionThe insect samples in all traps were collected after 48 hours and transported to the lab for analysis. The sticky traps were stored in the freezer, and the pitfall and pollinator traps were cleaned on a 120-mesh sieve immediately after collection and transferred in test tubes with 70% ethanol. Insects collected from these traps will be grouped as herbivores, predators, parasitoids, and pollinators and analyzed to determine the insect diversity, species richness, species evenness, and beneficial to pest ratio across the three treatments. Insect trap layout and timing will again be repeated in the fall of 2021. 

 Cash crop yield and pest damage 

Ninety days after planting, when the broccoli heads were ready to harvest, 5 random broccoli plants per treatment were photographed to evaluate pest damage. Each leaf on the plant was turned over to inspect for insects. Each plant was rated on a scale of 0-5; 0 meaning no insect damage and 5 indicating severe damage.  Insects on the leaves, when visible, were photographed for record. On the same day, yield measurements were taken for 10 randomly selected plants. The broccoli plants suffered mainly from frost bite from the freeze.   

 Soil health 

In the fall of 2020, we collected 6 soil cores to make one composite sample, each 0-20 cm deep, from each subplot in the same locations where the insect samples were collected. We maintained even spacing between each of these cores and were considerate of the distances of these cores from vine or plant trunks and irrigation lines. Holes were refilled to prevent a “swizz cheese” effect. Tools and gloves were disinfected with 90% isopropyl alcohol using a clean paper towel between each plot. Cores were mixed to make a composite sample by touching the outside of the bag and shaking well. A portion of soil samples were then transferred to 50 mL centrifuge tubes that were sealed and placed into a cooler with ice and transported to the labThe soil samples in the 50ml tubes were divided into 2 subsamples, ~30 g for PFLA and ~20 g for DNA extraction and stored in a freezer until analysis. Soil samples for PLFA were placed on dry ice and shipped overnight to the Water Management Research Unit. For the soil microbial community analysis, we currently extracting the DNA from 72 samples (samples from planting and harvest times) using the MP Fast DNA Spin Kit. These DNA samples will then be sent to the UT Austin DNA Sequencing Facility for the 16s sequencing. This will again be repeated for Fall 2021 planting season.  Additionally, during the fall season, we will collect root samples in both the cash crop and insectary strips to determine the total mycorrhizal colonization in the roots, nematode community, and the prevalence of plant parasitic nematodesWe will measure soil respiration biweekly with a 6400-09 Soil CO2 Flux Chamber. 

Research results and discussion:

Our preliminary results show that there was no difference in the yield of cash crops across the different treatments.  However, the broccoli heads across all treatments were not marketable due to frost damage. Overall, pest pressure appeared to be low, and we can assume this was due to the freeze killing the eggs. We hope the weather in the fall 2021 will be normal and a detectable difference can be determined. We will repeat our cash crop analysis in fall 2021. 

 

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

1 Webinars / talks / presentations
1 Workshop field days

Participation Summary

Education/outreach description:

Justin Lerma, an undergraduate student participating in this project did a poster presentation at the Engaged Scholar Award Symposium at UTRGV.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.