DOI: 10.5061/dryad.w3r22811p
title: Data from: Cover crops dismantle keystone ant/aphid mutualisms to enhance insect pest suppression and weed biocontrol

description: Cover crops are multifunctional tools that mitigate environmental impacts
 of agriculture, enhance resilience to weather extremes, and suppress weeds
 and arthropod pests. Cover crops provide non-crop food and habitat
 resources that attract natural enemies of pests, but their outcomes for
 pest management are less clear in regions where keystone mutualisms
 between red imported fire ants and aphids dominate. Here, we manipulate
 ant exclusion treatments and cover crop that vary in food/habitat
 resources treatments (living mulches and terminated cover crops), and
 examine responses of ants, aphids, and other herbivores and predators in a
 cotton agroecosystem. Living mulches reduced both ants and aphids in the
 crop canopy by 97% and 93%, respectively, relative to bare soil
 treatments, and terminated cover crops reduced them as well by a lesser
 degree (~50%). Non-aphid herbivores occurred in low densities system-wide,
 and increased in living mulches, while native predators had variable
 responses to cover crops and ant exclusion. Cover crops had no effect on
 prey removal in the crop canopy, but living mulches tripled rates of weed
 seed biocontrol relative to bare soils. Cover crops elicited a shift in
 fire ant foraging from cotton foliage downward to the soil-surface,
 preventing competitive exclusion by keystone ant/aphid mutualists that
 dominate crop monocultures. Cover crops altered the system-wide impacts of
 fire ants: reducing ecosystem disservices (i.e. aphid tending), and
 enhancing ecosystem services (i.e. weed seed biocontrol). These results
 provide incentives for cover crop adoption as a regenerative practice in
 large-scale commercial agriculture.
description: Our experiment compared four cover crop treatments in a
 conventional, reduced-tillage cotton (<em>Gossypium
 hirsutum</em>) agroecosystem: 1) white clover living mulch
 (<em>Trifolium repens ‘Durana</em><sup>®</sup>’),
 2) terminated cereal rye (<em>Secale cereale </em>‘Wrens
 Abruzzi’), 3) terminated crimson clover (<em>Trifolium incarnatum
 </em>‘Dixie’), and 4) a bare ground treatment (Fig. 1). Terminated
 cover crop treatments were selected because they are commonly implemented
 conservation practices in agronomic crops regionally (Hill et al., 2021;
 Vaan et al., 2018, Weisberger et al. 2024)), and encouraged in control of
 <em>Amaranthus palmeri</em> which herbicide sites of action
 are rendered inadequate without an additional tool for weed control
 (Weisberger et al. 2024). The living mulch was selected because
 Durana<sup>®</sup> clover has been optimized recently as a
 perennial groundcover in field crops with great promise for improving soil
 health and augmenting nitrogen fertility budgets (Hill et al. 2021;
 Sanders et al. 2017). The four cover crop treatments were randomized in
 four replicated blocks (16 main plots total) that were 10.9 m wide and
 16.5 m long. There was no space between plots within each block, and 11 m
 alleys separating blocks were planted to cereal rye. Each main plot
 contained 12 rows of cotton plants with 90 cm row spacing. Within each
 main plot, we manipulated two ant manipulation subplot treatments (‘ant
 exclusion’, and control). Each plot also contained a subplot where
 <em>A. palmeri </em>seeds were sown, to examine effects of
 cover crops on suppression of the herbicide-resistant weeds (reported
 separately in Weisberger et al. 2024). The cover crop
 trial was originally established on October 3rd, 2019 in a cotton field
 and was chisel plowed and disked for seedbed preparation that same day.
 Cover crop treatments were planted on October 18th, 2019 with a Great
 Plains<sup> </sup><sup>Ⓡ</sup> no-till drill at
 the following rates: Cereal rye at 112 kg/ha, large seed box D2-65);
 crimson clover was planted at 22 kg/ha with a small seed box - 85), and
 white clover living mulch planted at 22 kg/ha with a small seed box - 80).
 Cereal rye and crimson clover were replanted every year in mid-November
 (after cotton harvest) for three years at the same rate. After year 3 of
 cotton harvest, living mulch was replanted on November 21st, 2022, and
 again in Feb 2023 due to poor germination. Cereal rye was terminated with
 a roller crimper on May 10, 2023, and glyphosate and dicamba were applied
 to cereal rye, crimson clover, and bare ground plots at 3.12 kg a.i. /
 ha), as well as within cotton rows in 0.2 m bands in living mulch
 treatments (Weisberger et al., 2024). Cotton cultivar ‘DG 3615 B3XF’, a Bt
 hybrid with herbicide tolerance, was planted with the no-till drill seeder
 five days after herbicide treatments were applied on May 24, 2023, at
 38,000 seeds/ha (about 12 cm apart within rows), and follow-up herbicide
 treatments were applied on June 16 and July 12, 2023 (glufosinate at 2.3 L
 / ha). On June 29th, 2023, two ant manipulation subplot
 treatments were established within each plot: 1) 'ant exclusion’
 treatments, where ants were physically prevented from accessing four
 plants in a row, and ‘control’ treatments, where ants were allowed access
 to the plants. In ant exclusion treatments, a band of tape 5 cm wide was
 secured just below the bottom-most leaves at the bases of four consecutive
 plants. The tape was covered in Tanglefoot<sup>Ⓡ</sup> sticky
 barrier similar to experimental ant exclusion treatments applied on wild
 cotton plants by Rudgers (2004). Data were not collected on the outer two
 plants in the ant-manipulation subplots to reduce effects of ants
 immigrating from neighboring plants. Each plot contained two
 pseudoreplicates of ant manipulation treatments (four subplots total),
 which were selected randomly and were &gt;6 m apart. All
 pseudoreplicates were pooled at the plot level prior to
 analysis. <em>Insect
 sampling</em> <em>Visual surveys:
 </em>One week after ant exclusion treatments were established, we
 began visual surveys of insects on cotton plants. No data were collected
 from cotton plants in the outer two rows to minimize border
 effects.<em> </em>We conducted visual surveys on the two inner
 plants of the ant manipulation subplots by counting and identifying all
 insects on the leaves, stems, and flowers on the entire cotton plant. We
 identified all insects at the family level on-site. Visual surveys
 occurred weekly (three sample dates) on July 7, July 14, & July
 21, 2023.   <em>Vacuum sampling: </em>To
 examine cover crop effects on highly mobile pests and natural enemies not
 easily sampled in visual surveys, we also vacuum sampled ten cotton plants
 outside the ant manipulation subplots with a leaf blower modified in
 suction mode with a funnel and a mesh bag for capturing insects. We did
 not vacuum our experimental ant manipulation subplots, to avoid disturbing
 that experimental treatment. Ten plants in a single row of each plot were
 suctioned for three seconds each. Insects were transferred to 70% ethanol
 and stored for later identification. This survey was conducted once on
 July 7, 2023. <em>Pitfall traps:</em> To
 examine how cover crops influenced ants at the soil surface, pitfall traps
 were set at two randomly selected locations in each plot for 72 h on July
 14, 21, and 28. Because many traps were flooded after rain events or lost
 to wildlife damage in the second and third weeks, we only analyzed pitfall
 samples from July 14, when no traps were missing. Pitfall traps consisted
 of a 1 L deli cup sunk into the soil flush with the soil surface. After
 samples were collected, insects were stored in 70% ethanol for later
 identification. <em>Estimating biological
 control</em> To estimate insect predation, we
 secured 25 frozen fly pupae to 2 cm x 3 cm cardstock with double-sided
 carpet tape, covered the remaining sticky residue with sand, and attached
 them to cotton leaves with paper clips. We attached two cards per plot,
 one on a plant with the ant exclusion treatment, and one on a control
 plant. Pupae cards were collected after approximately 24 hrs. This survey
 occurred on July 13, and July 25, 2023.
description: # Cover crops dismantle keystone ant/aphid mutualisms to enhance insect
 pest suppression and weed biocontrol --- This dataset includes results
 from experimental manipulations of cover crop treatments and ant exclusion
 treatments made to cotton plants in 16 experimental research plots grown
 at UGA's Campbell Research Farm in summer 2023. On each cotton plant,
 we counted herbivorous pest insects, red imported fire ants, and predatory
 arthropods. It also includes pitfall trap samples of fire ants active at
 the soil surface, and vacuum samples of mobile insects in cotton foliage.
 It also includes estimates of weed seed removal from seed caches at the
 soil surface and insect prey removal from the cotton canopy. ##
 Description of the Data and file structure Missing data (when samples were
 lost or damaged) are noted as "n/a" throughout the data set.
 This spreadsheet contains five sheets: **Sheet 1 (visual survey)**
 contains annual sums of insects visually observed on crop foliage within
 each of the cover crop main plot treatments and ant exclusion sub-plot
 treatments, pooled across all sample dates; **Sheet 2 (vacuum sample)**
 contains sums of insects vacuum-sampled from cotton foliage in cover crop
 main plot treatments on one sample date in 2023; **Sheet 3 (pitfall
 trap)** contains counts of red imported fire ants sampled in pitfall traps
 in each main plot on one sample date in 2023; **Sheet 4 (weed seed
 predation)** contains proportions of weed seeds removed from experimental
 caches placed at the soil surface in main plots in 2023; **Sheet 5 (pupa
 predation)** contains proportions of fruit fly pupae removed from
 experimental caches placed in cotton foliage within cover crop main plot
 treatments and ant exclusion subplot treatments in 2023 #### **Metadata:**
 **Descriptions of column headers:** * plot: numbered plot identifier
 (1-16) * block: alphabetical block identifier (A-D) * cover.treatment:
 Experimental cover crop treatment (bare soil, red clover, rye, living
 mulch) applied to each main plot. * ant.treatment: Ant exclusion
 treatments (control, ant exclusion) applied to subplots within each main
 plot. * ants: Annual means of ants counted on 8 zucchini plants for all
 sample dates. * aphids: Annual means of aphids counted on cotton plants
 for all sample dates. * herbivores: Annual means of herbivorous
 (non-aphid) insects counted on cotton plants for all sample dates. *
 predators: Annual means of predatory arthropods counted on cotton plants
 for all sample dates. * date: Month/day/year observations were made. *
 insect: Common name identification of insects captured in vacuum samples
 on cotton plants in main plots. * count: Quantity of insects captured in
 vacuum samples on cotton plants in main plots. * trophic level:
 Categorical identifier of insects' trophic level (herbivore, natural
 enemy) * proportion.seeds.removed: Proportion weed seeds removed from
 experimental caches at the soil surface in each main plot. *
 proportion.pupae.removed: Proportion fruit fry pupae removed from
 experimental caches in the cotton foliage in each subplot. Missing data
 (when samples were lost or damaged) are noted as "n/a"
 throughout the data set. ## Sharing/access Information Links to other
 publicly accessible locations of the data: N/A Was data derived from
 another source? No.