The hoverfly Eristalinus aeneus is an important pollinator of crops and wild plants. However, there is a lack of detailed information about its foraging behaviour and its potential as a managed pollinator of mango. Given the growing economic importance of protected cultivation of mango, our aim is to study the flight activity and foraging behaviour of E. aeneus on this crop. Eristalinus aeneus displayed a bimodal daily activity, with peaks during mid-morning and mid-afternoon. The activity was maintained over a wide range of temperature (from 17.8 up to 37.4°C), light intensity (from 8.2 up to 57.4 klux) and relative humidity (from 19.0 up to 88.8%). The syrphids were active most of the time in this crop, and we observed five different types of activity: foraging (67%), resting (17%), flying (10%), grooming (4%) and walking (2%). This hoverfly visited hermaphrodite flowers more often than male flowers. On average, it visited 36.46 ± 13.92 flowers per 5 min, with a higher number of floral visits for nectar feeding. The duration of the visits to hermaphrodite and male flowers was similar but pollen-feeding visits lasted longer (6.44 s per flower) than nectar-feeding ones (5.51 s per flower). The highest number of visits to mango inflorescences was observed during the morning, but the longest visits occurred at midday. The implication of these results for the potential use of E. aeneus as a managed pollinator in protected cultivation of mango is discussed.

Hybrid seed production often relies on managed pollinators whose use in isolation cages can pose challenges. Here, we evaluated the pollination ability of the novel managed pollinator Eristalinus aeneus (Diptera: Syrphidae) in hybrid celery and fennel seed crops. During trials performed in 2019–2020 in Cordoba, Spain, we compared seed production with hoverflies released at high and low densities (40–20 ind./m2), and without released pollinators. In celery, we included a treatment with Lucilia sericata (Diptera: Calliphoridae), a blowfly used for seed production (375 ind./m2). The production of celery seeds when E. aeneus were released at high density was significantly higher (+49%) than without released pollinators, for both sterile and fertile plant genotypes; no significant differences were found between the two hoverfly densities and the blowfly treatments. In fennel, seed yield of fertile plants with high density of hoverflies was higher than with low density (+149%), or without released pollinators (+168%); whereas for sterile plants no differences were found between treatments. In both crops and plant genotypes, the highest pollen adhesion to stigmas (number of pollen grains and proportion of flowers with pollen adhered in two stigmas) was obtained with hoverflies at high density. In celery, pollen adhesion was higher with high density of hoverflies than with blowflies for both plant genotypes, despite the considerably lower numbers of released hoverflies. Our results suggest that E. aeneus is a more efficient pollinator of celery than L. sericata, and that it has the potential to effectively pollinate other hybrid Apiaceae seed crops like fennel.

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Watermelon (Citrullus lanatus) is an important crop worldwide. Pollination of this crop is carried out by insects, with honey bees (Apis spp.) and bumble bees (Bombus spp.) as the most used in greenhouse production. Nevertheless, due to the extreme conditions in closed enclosures, these hymenopterans suffer management and behavior problems leading to insufficient pollination. The effectiveness of three release densities (15, 30, and 45 individuals/m2) of Eristalinus aeneus was compared in diploid- and triploid-associated watermelon varieties under protected cultivation. Floral visits, pollen–pistil interaction after pollen transport, yield, and fruit quality were evaluated. The number of floral visits increased with release density in both pistillate and staminate flowers. No significant differences were observed, however, among release densities or between flower types in the duration of the visits. Floral preferences were not found in the behavior of E. aeneus in watermelon. High and medium release densities increased pollen deposition onto the stigma, and consequently the yield of the triploid variety compared to low release density, by 23.8 to 41.8% in 2020 and by 36.3 to 46.7% in 2021. The results of this trial demonstrate the potential of E. aeneus as a managed pollinator in protected cultivation of triploid watermelon.