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

View the project final report

Commodities

• Vegetables: onions, peppers

Practices

• Pest Management: biological control, integrated pest management
• Production Systems: agroecosystems
• Soil Management: soil quality/health

Farm edges are generally the most undisturbed areas in a farm with diverse vegetation and can enhance agrobiodiversity and provide crucial food and shelter for wildlife, insects, and soil biota. Planting native wildflowers with the ability to reseed and withstand local climatic conditions for semi-permanent vegetation around farm edges or in between crops has potential to biologically control pests. To test this, we ran a two-year study and installed three different flowering insectary strips on a certified organic vegetable farm in South Texas during the winter season. The treatments were: 1) a commercially sourced 17-species native wildflower seed mix; 2) sunn hemp (Crotalaria juncea); and 3) weeds that spontaneously germinated. We collected pitfall traps, sticky traps, and blue-vein pollinator trap to capture above ground arthropods and ran PFLAs to determine the proportions of soil microbes. Our results show that the soil microbial communities were influenced by treatment, location, and time. The middle of the insectary strips had significantly higher fungal to bacterial ratios and gram-negative proportions compared to the cash crops. Arthropod communities were influence by time and location but not treatment. Traps collected later in the season showed fewer pests (main order Hemiptera) and more beneficials (main orders Coleoptera and Hymenoptera) in the middle of the insectary strip compared to the cash crop.

Experimental Design

We established a randomized block experimental design to test the multiple benefits of insectary strips at a certified organic vegetable farm in Edinburg, Texas. Soil was cross-disked and bedded to terminate the weeds and conserve soil moisture, both of which are standard practices for farmers in South Texas. The planting beds were 1.5 meters wide from one center of a bed to the next. There was an insectary strips between every four beds of cash crop. The topsoil was raked 2.5 cm deep. Sunn hemp and native seeds were broadcasted by hand and covered to ensure soil to seed contact. A 3-meter buffer was continuously weeded to separate one treatment side from the other. For the first year, insectary strips were planted on October 2, 2020, and the cash crop seedlings were transplanted on December 10, 2020, in two rows, 45 cm apart, in a staggered manner for a total of five plants per bed. In year two, the insectary strips were planted on Aug. 15, 2021, and the cash crop seedlings were transplanted on Oct 5, 2021, in two rows, 30 cm apart, for 10 plants per bed.  

Data collection: Insects

To examine the arthropod community dynamics, three types of traps were employed to collect arthropod community structure data present in the region. We used odorless sticky traps (Pherocon® AM Yellow; Trece, Inc., Adair, OK, USA) and pitfall traps filled ¼ths with water and a couple of drops of odorless soap (Micro-90 odorless detergent (Cole-Parmer, catalog number: SK-18100-05) to break the surface tension of the water. These two traps were placed in the middle of the insectary strips, the edge of the insectary strips, and the middle of the cash crop row, approximately 3 meters from the insectary strip. Blue Vane pollinator traps (BanfieldBioTM Inc., Seattle, WA) with yellow collection jars were only placed in the middle of the insectary strips

Data collection: Soil

Soil samples were collected at two different times, two weeks after cash crops were transplant (early) and at-harvest (late). In year one, samples were collected on December 15, 2020 (early), and March 8, 2021 (late). In year two, samples were collected on December 15, 2021 (early), and February 5, 2022 (late). A total of three subsamples were collected from each plot with a soil corer with a 2.5 cm diameter (AMS, American Falls, ID) to a depth of 0-20 cm with even spacing between each core, avoiding drip line and plant roots. Probe, spatula, and gloves were cleaned with water then 80% ethanol (Fisher Scientific Waltham, MA, USA) in between each treatment block. The mixed composite samples were transferred to a 50 mL centrifuge tube and placed in a -80 °C freezer until shipped on dry ice to the lab for analysis. Note, year one samples were analyzed at the San Joaquin Valley Agriculture Sciences Center (Parlier, California, USDA-ARS) and year two samples were analyzed at WARD Laboratory (Kearney, Nebraska, USA). 

Cash crops

To determine impact on cash crop and plant fitness, we collected fruit weight for 10 plants per treatment block (n = 180), took the weight of each broccoli head in year one and the weight of the total number of peppers per plant. To determine pest-induced damaged, five broccoli plants were rated on a scale of 0 to 5 (least to worst) and percentage of damaged pepper for each plant was calculated.