DOI: 10.5061/dryad.8pk0p2nv7
title: Crop diversity and within field multi-species interactions mediate herbivore abundances in cotton fields

description: Insect herbivore abundances in agricultural fields partly depend on
 surrounding landscape compositional heterogeneity (e.g., landscape
 complexity). Landscape complexity can directly (e.g., dilution of host
 crops) and indirectly (promoting herbivore biocontrol) regulate herbivores
 in agricultural fields. While much is known about direct (e.g.,
 resource concentration) and indirect effects (i.e., promoting biocontrol)
 of landscape complexity on herbivore populations, more work is needed to
 study whether landscape complexity can regulate herbivore populations by
 mediating within field multi-species interactions among herbivores and
 their shared natural enemies. During 2019 and 2020, we estimated
 Bemisia tabaci and Aphis gossypii abundances, their dominant predators
 (coccinellids, spiders, Orius spp., and Geocoris spp.), and their
 interaction (using molecular analysis) in 38 cotton fields along a
 gradient of landscape diversity across Georgia, USA. Within
 cotton fields, we assessed the effect of predator abundances, their
 frequency of feeding on herbivores, and the correlation between herbivore
 abundances (B. tabaci and A. gossypii) on the B. tabaci and A. gossypii
 abundance. At the landscape scale, crop diversity and different cover
 types influenced the abundance of B. tabaci and A. gossypii within cotton
 fields. We found a complex interaction among pests at the field scale,
 with higher aphid abundance correlated with decreased whitefly abundance.
 Our results support crop diversification for improving suppression of
 generalist pests in cotton landscapes through promoting biocontrol and
 diluting host crop area. Our result further suggests that the landscape
 complexity effect on whiteflies can indirectly mediate aphid abundance in
 cotton fields, indicating the importance of within field species
 interactions.
description: <strong>Abundance of herbivores and predators
 </strong> In each sampled cotton field, we
 assessed the abundance of pests (i.e., cotton aphids, sweetpotato
 whitefly) and predators using forty 180-degree sweeps with a 38 cm
 diameter sweep net (0.1 mm openings). Twenty sweeps were collected along a
 20 m transect in the border (i.e., 5 meters inside the field from the main
 road) and 20 sweeps towards the center of the field parallel to the border
 transect (i.e., 50 m into the field from the border). The average cotton
 field size in our study area was 36 hectares. Our sampling design allowed
 us to investigate the effect of the sampling location on predator and pest
 counts. Given the low abundance of whitefly and aphids in sweep-net
 samples in the 2019 field season (e.g., the immature stage of whitefly is
 attached to the leaf and occasionally found in sweep-net), we collected
 leaf samples (i.e., five leaves were haphazardly collected within each
 transect/ one leaf per plant) along with sweep-net in the 2020 field
 season to improve estimates of aphid and whitefly abundance (i.e., adults
 and immature combined) in cotton fields. After collection, we transferred
 sweep-net content to plastic bags and separated the predators in the field
 using aspirators. We transferred each predator into a separate 1.5 mL
 Eppendorf vial containing 99% ethanol and stored them in a cooler (~3-4 h)
 to minimize the possibility of DNA contamination (i.e., reduce the
 interaction period between predators and pests within sweep-net) and
 minimize degradation. Similarly, we transferred the leaf samples into
 plastic bags and stored them in the cooler. In the laboratory, we stored
 the sweep-net content and leaf samples inside a -20°C freezer until
 processing. Sweep-net and leaf samples were carefully checked under a
 microscope (Leica MZ APO, Leica Microsystems Ltd, Switzerland) to identify
 predators and pests using identification keys to the family and genus
 levels (Triplehorn et al., 2005; Ubick et al., 2017). The numbers of pests
 and predators were recorded, and predator samples were stored in a -20°C
 freezer until DNA extraction. <strong>Landscape
 quantification</strong> Georeferenced maps with
 crop and non-crop quantifications were obtained from CropScape (USDA
 National Agricultural Statistics Service, https://nassgeodata.gmu.edu/CropScape/) online map resources. The percentage area of each cover type (e.g., crops and non-crops) in the surrounding 2 km of the focal cotton field were quantified using ArcMap 10 version 10.7.1 (ArcGIS, 2021). Given no previous work on the effect of landscape complexity on whiteflies, we tested four spatial scales (0.5, 1, 1.5 and 2km) to determine the scale at which the landscape complexity had the most impact on whiteflies and their control. Twenty-seven cover types were identified within a 2 km radius around the 38 cotton fields (Figure S1 & S2, Table S2). Among these, 20 were crops, and 7 were semi-natural habitats. The major crops in these agricultural landscape regions were cotton, peanut, corn, and woody crops (notably, perennial fruit trees such as peach, blueberries and pecans). The less abundant crops (namely, crops with lower than 4% average coverage in the landscape) were merged into the other-crops category. The major semi-natural habitats were forests, wetlands, grasslands (all grassy areas including field margins), shrubland and pasture. The water bodies, including rivers and ponds, were merged into the water category. We used vegan package in R (Oksanen et al., 2015) and estimated overall landscape habitat diversity (i.e. Simpson diversity of all land cover types in a given buffer area, Simpson 1949). Similarly, crop diversity was estimated by excluding non-crop habitats from the landscape using the Simpson diversity index.
description: # Crop diversity and within field multi-species interactions mediate
 herbivore abundances in cotton fields
 [https://doi.org/10.5061/dryad.8pk0p2nv7](https://doi.org/10.5061/dryad.8pk0p2nv7) ## Description of the data and file structure ## Herbivore\_abundance-cotton\_leaf\_samples.csv This dataset is used to determine associations between whitefly and aphid abundance in cotton fields and agricultural landscape complexity in multiple spatial scales. This dataset was further used to determine within-field predator-prey interactions and their impact on whitefly and aphid abundance in cotton fields. Notes\* The covertpe values represent the percentage of each crop/non-crop habitat in the landscape within the represented spatial scale. The predator and pest values represents the number of collected individual in each field (40 sweeps total). 1 The field identification indicates the county where the sample was collected in the State of Georgia. 2 The latitude of the sampled cotton field in Georgia. 3 The longitude of the sampled cotton field in Georgia. 4 The spatial scale at which the percentage covertypes is estimated in the landscape. 5 Merged value of all crops with less than 3% coverage in the landscape. 6 Merged value of all woody crops including blueberries and peaches in the landscape. 7 Merged value of all annual crops including cotton and peanuts, in the landscape. 8 Merged value of all wooded areas in the landscape. 9 Merged value of all habitats with plants that are not crops. 10 Merged value of all habitat types that are not crops, including urban areas, roads, and water bodies. 11 The total number of whitefly per field, calculated by counting whitefly numbers on ten cotton leaves per field. 12 Indicates the total number of predators (Coccinellids, Geocoris, Orius and spiders combined) screened for feeding on whiteflies and aphids in cotton fields. 13 The number of predators positive for whitefly DNA from the total number of screened predators. 14 The proportion of predators positive for whitefly DNA. The proportion was calculated by dividing the number of positives by the total number of tested predators. 15 The number of predators positive for cotton aphid DNA from the total number of screened predators. 16 The proportion of predators positive for cotton aphid DNA. The proportion was calculated by dividing the number of positives by the total number of tested predators. ## Predator\_abundance\_1920\_sweepnet.csv This dataset is used to determine associations between predator abundance in cotton fields and agricultural landscape complexity in multiple spatial scales. Notes\* The covertpe values represent the percentage of each crop/non-crop habitat in the landscape within the represented spatial scale. The predator and pest values represents the number of collected individual in each field (40 sweeps total). 1 The field identification indicates the county where the sample was collected in the State of Georgia. 2 The latitude of the sampled cotton field in Georgia. 3 The longitude of the sampled cotton field in Georgia. 4 The spatial scale at which the percentage covertypes is estimated in the landscape. 5 The year of data collection, and landscape quantification. 6 Merged value of all crops with less than 3% coverage in the landscape. 7 Merged value of all woody crops including blueberries and peaches in the landscape. 8 Merged value of all annual crops including cotton and peanuts, in the landscape. 9 Merged value of all wooded areas in the landscape. 10 Merged value of all habitats with plants that are not crops. 11 Merged value of all habitat types that are not crops, including urban areas, roads, and water bodies. 12 The total number of whitefly per field calculated by counting whitefly numbers in 40 sweeps in cotton fields. ## WF-AP\_predation\_data-1920\_sweeps.csv This dataset is used to determine associations between whitefly and aphid predation in cotton fields and agricultural landscape complexity in multiple spatial scales. Notes\* The covertpe values represent the percentage of each crop/non-crop habitat in the landscape within the represented spatial scale. The predator and pest values represents the number of collected individual in each field (40 sweeps total). 1 The field identification indicates the county where the sample was collected in the State of Georgia. 2 The latitude of the sampled cotton field in Georgia. 3 The longitude of the sampled cotton field in Georgia. 4 The spatial scale at which the percentage covertypes is estimated in the landscape. 5 The year of data collection, and landscape quantification. 6 Merged value of all crops with less than 3% coverage in the landscape. 7 Merged value of all woody crops including blueberries and peaches in the landscape. 8 Merged value of all annual crops including cotton and peanuts, in the landscape. 9 Merged value of all wooded areas in the landscape. 10 Merged value of all habitats with plants that are not crops. 11 Merged value of all habitat types that are not crops, including urban areas, roads, and water bodies. 12 The total number of whitefly per field calculated by counting whitefly numbers in 40 sweeps in cotton fields. 13 Indicates the total number of predators (Coccinellids, Geocoris, Orius and spiders combined) screened for feeding on whiteflies and aphids in cotton fields. 14 The number of predators positive for whitefly DNA from the total number of screened predators. 15 The proportion of predators positive for whitefly DNA. The proportion was calculated by dividing the number of positives by the total number of tested predators. 16 The number of predators positive for cotton aphid DNA from the total number of screened predators. 17 The proportion of predators positive for cotton aphid DNA. The proportion was calculated by dividing the number of positives by the total number of tested predators.