Comparison of hand netting and pan trapping methods for estimating hover fly (Diptera: Syrphidae) diversity in the tropical agroecosystems of East Africa
Data files
Dec 04, 2025 version files 3.21 MB
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Meta_data.xlsx
3.21 MB
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README.md
2.85 KB
Abstract
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.
Dataset DOI: 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 (>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.
Hover fly sampling was conducted using two complementary methods—hand netting and yellow pan traps—following modified protocols of Gervais et al. (2018) and Power et al. (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 et al., 2007; Westphal et al., 2008). Yellow traps were chosen to reflect the dominant flower colour of cucurbits and their proven attractiveness to pollinators (An et al., 2018; Farbenlernen et al., 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.