DOI: 10.5061/dryad.4xgxd25q6
title: Comparison of hand netting and pan trapping methods for estimating hover fly (Diptera: Syrphidae) diversity in the tropical agroecosystems of East Africa

description: Monitoring hover fly populations is essential for establishing baseline
 data on community dynamics and their potential links to ecosystem service
 provision. While pan traps and hand netting are widely used in monitoring
 insects in natural habitats, their comparative performance in estimating
 hover fly (Diptera: Syrphidae) diversity in Afrotropical agroecosystems
 remains understudied. This study assessed the effectiveness of yellow pan
 traps and hand netting over two consecutive years (2022–2023) in a
 cucurbit agroecosystem in Morogoro, Tanzania, across two contrasting
 landscapes (plateau and mountainous zones). Weekly sampling was conducted
 for eight consecutive weeks during both the rainy (April–June) and dry
 (September–November) seasons across 20 cucurbit plots. In each plot, nine
 yellow pan traps were deployed for 48 hours, and hand netting was
 conducted along three 15-m transects for 45 minutes per session. Hand
 netting consistently recorded higher hover fly diversity than pan traps
 across all Hill numbers (q = 0, 1, 2). Species accumulation curves reached
 asymptotes more rapidly with hand netting, indicating greater sampling
 efficiency and community coverage. Although more labour-intensive, hand
 netting provided a more comprehensive estimation of hoverfly diversity in
 both agroecological zones. In contrast, pan traps captured only a few
 additional low-abundance species overlooked by netting, which are unlikely
 to contribute significantly to ecosystem service provision. Therefore,
 hand netting proved to be the most robust and cost-effective method for
 monitoring hover flies in agricultural landscapes. These findings provided
 evidence to support the development of standardized monitoring protocols
 for hover flies in tropical agricultural landscapes.
description: Hover fly sampling was conducted using two complementary
 methods—hand netting and yellow pan traps—following modified protocols of
 Gervais <em>et al.</em> (2018) and Power <em>et
 al.</em> (2016). For hand netting, three permanent 15 m transects
 were set per subplot, 15 m apart and 7.5 m from plot edges. Sampling
 occurred weekly during cucurbit flowering, for 15 minutes per transect
 within a 2 m belt, on warm sunny days. Specimens were collected into
 ethanol-filled tubes. For passive sampling, three yellow pan traps (15 cm
 diameter) were randomly placed between transects to avoid spatial bias and
 capture natural microhabitat variability (Roulston <em>et
 al.</em>, 2007; Westphal <em>et al.</em>, 2008). Yellow
 traps were chosen to reflect the dominant flower colour of cucurbits and
 their proven attractiveness to pollinators (An <em>et
 al.</em>, 2018; Farbenlernen <em>et al.</em>, 2018).
 Traps containing 300 ml of soapy water were left for 48 hours. Collected
 hover flies were preserved in ethanol, identified morphologically under
 stereomicroscopes by S.K. and K.J., and voucher specimens were deposited
 at the Sokoine University of Agriculture (SUA) and the Royal Museum for
 Central Africa (RMCA), Belgium.
description: # Comparison of hand netting and pan trapping methods for estimating hover
 fly (Diptera: Syrphidae) diversity in the tropical agroecosystems of East
 Africa Dataset DOI:
 [10.5061/dryad.4xgxd25q6](https://doi.org/10.5061/dryad.4xgxd25q6) ##
 Description of the data and file structure The study was conducted in the
 Morogoro Region, Eastern Tanzania, from April 2022 to November 2023,
 across two contrasting agroecological zones (plateau and mountainous). The
 plateau (300–600 m a.s.l.) receives 700–1200 mm annual rainfall with a
 mean temperature of 29 °C, while the mountainous zone (&gt;900 m) receives
 800–2500 mm and averages 24 °C. Ten 45 × 45 m plots per zone were
 established at least 50 m apart. Three cucurbit crops—cucumber (*Cucumis
 sativus* L.), watermelon (*Citrullus lanatus* (Thunb.) Matsum. &
 Nakai), and squash (*Cucurbita moschata* D.)—were planted in 45 × 15 m
 subplots using standard spacing (50 × 60 cm for cucumber; 1.5 × 1.5 m for
 watermelon and squash). Fields were maintained under comparable agronomic
 practices across zones, including manual weeding, organic and inorganic
 fertilization, and pest management using both pesticidal plants and
 synthetic pesticides. ### Files and variables #### File: Meta_data.xlsx
 **Description: **Species richness, total abundance, Shannon, and Simpson
 diversity indices were calculated from the data. These response variables
 were analyzed using models that included trapping method (TM) and
 agroecological zone (AL) as fixed factors, along with their interaction
 term (TM × AL). Field identity (FN), nested within agroecological zone,
 and season (SE) were included as random factors to account for potential
 spatial and temporal dependencies in the data. ID_formatted: Unique
 identifier for each sample/observation Trapping: Method used to collect
 insects (e.g., pan trap, sweep net) Year: Year the sample was collected
 season_nested_in_year: Seasonal code within the year season_1_4: Combined
 year-season code collection_date: Exact date of collection (day-month)
 week_n: Week number during which the sample was collected (e.g., W008)
 range_months: Broad period or months of collection (e.g., Sept_Nov_2022)
 field: Field or location of collection altitude: General altitude category
 (e.g., low, medium, high) altitude_masl: Exact altitude in meters above
 sea level management: Type of crop management (e.g., conventional,
 organic) crop: Crop species at the collection site replicate: Replicate
 number of the sample (for multiple samples in the same plot) latitude:
 Geographic latitude of the collection site longitude: Geographic longitude
 of the collection site total_catch: Total number of insects caught in the
 sample column R to BT: Counts of each insect species collected ##
 Code/software Microsoft Excel can be used to view the data file.