Do laboratory-reared flies perform differently as pollinators? Morphology, behaviour and pollination performance of Eristalis tenax (Syrphidae)

Flies (Diptera) are important pollinators in global agriculture, yet little is known about how intraspecific trait variation influences their pollination performance. We compared morphological traits, foraging behaviour and pollination-related performance metrics between laboratory-reared (hereafter lab-reared) and wild populations of Eristalis tenax (Diptera: Syrphidae) in hybrid seed carrot (Daucus carota L.) under semi-controlled field conditions using in-field cages in the Riverina region of New South Wales, Australia. Lab-reared flies were significantly larger than wild flies in body length, inter-tegular distance, and thorax width. Single-visit deposition assays showed that both fly populations deposited more pollen than unvisited control flowers, with lab-reared flies pollinating 3.5× more stigmas per visit and depositing 4.6× more pollen on pollinated stigmas per visit. Seed set was highest in umbels pollinated by lab-reared flies (25.9%), followed by wild treatments (16.4%) and negligible in bagged controls (0.01%). Although umbels pollinated by lab-reared flies produced 1.5× higher seed numbers, fresh seed weight did not differ between lab-reared and wild treatments, indicating that differences in seed set were not accompanied by detectable differences in seed mass under the conditions tested. Additionally, foraging activity differed between populations: lab-reared flies showed higher activity on male umbels during early morning periods (05:00–08:00) and within moderate temperature (20°C–30°C) and humidity (33%–66%) ranges, whereas wild flies exhibited more consistent activity across the day (05:00–17:00), visited male and female umbels in similar proportions, and remained active across a broader humidity range (0%–99% RH). Together, these results indicate population-level differences in morphology and foraging behaviour that influence pollination-related metrics under semi-controlled conditions. Our findings suggest that lab-reared E. tenax can perform comparably to wild conspecifics in hybrid seed carrot systems, with context-dependant advantages that may be leveraged in managed pollination strategies.