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.

Aphidophagous hoverflies (Diptera, Syrphidae, Syrphinae) are common flower visitors and aphid predators in a range of flowering plants, including fruit crops. Here, we investigate whether aphid prey DNA can be detected in the gut contents of hoverfly larvae from a commercial strawberry field as a proof of concept that a molecular approach can be used to measure agricultural biocontrol. We used high-throughput sequencing (HTS) to target insect DNA and compared the resulting data to reference databases containing aphid and hoverfly DNA sequences. We explored what impact incorporating wildflowers within polythene-clad tunnels may have on aphid DNA detection rates in hoverfly larvae. In a randomized block experiment, coriander (Coriandrum sativum), field forget-me-not (Myosotis arvensis) and corn mint (Mentha arvensis) plants were inserted in rows of strawberries. Their effect on aphid DNA detection rates was assessed. Aphid DNA was found in 55 of 149 specimens (37%) validating the method in principle for measuring agricultural services provided by hoverflies. Interestingly, detection rates were higher near plots with forget-me-not than plots with coriander, though detection rates in control plots did not differ significantly from either wildflower species. These findings confirm that hoverflies predate aphids in UK strawberry fields, and that HTS is a viable method of identifying aphid DNA in predatory hoverflies. We comment on the need for further method development to narrow down identifications of both predator and prey. We furthermore provide some evidence that there is an effect of intercropping strawberry crops with wildflowers which may affect aphid consumption in hoverfly larvae.

Eristalinus aeneus (Scopoli, 1763) is a suitable candidate for artificial rearing due to its pollination efficiency and subcosmopolitan distribution. However, the high mortality found at the larval stage of this species needs to be overcome. In this research, two different larval media were used to study the life cycle of E. aeneus: brewery spent grain (BSG) from a local craft-beer factory and soaked oat grains (SOG). The age-stage, two-sex life table method was used to analyze the results, which were compared using the paired bootstrap test. The greatest mortality was found at the larval stage with both media. Individuals fed on SOG presented a shorter preadult developmental time (22.05 days) than those reared with BSG (26.97 days). This fact had a direct impact on the total preoviposition period, it being shorter with SOG (34.36 days) than BSG (38.29 days), although the second provided a larger total number of eggs (19,242 eggs) and a faster adult maturation (10.67 days). The population parameters indicated that both populations will display a positive growth under the studied conditions, being the mean generation time (T) significantly shorter when using SOG (38.71 days) than BSG (45.95 days). Despite the preadult results pointing to SOG being a more efficient medium, the promising fecundity values provided by BSG, as well as it's lower cost and ecological benefits, suggest that this second medium could be improved and used as an alternative to SOG in the near future.

We report the establishment of two representatives of a new ecological functional group on the sub-Antarctic island of South Georgia - pollinating insects - in the form of the hoverfly Eristalis croceimaculata Jacobs (Diptera, Syrphidae) and the blowfly Calliphora vicina Robineau-Desvoidy (Diptera, Calliphoridae). The floricolous adults of these two species provide a new ecological role, pollination, in the ecosystems of this island. The activity of their respectively saprophogous or necrophagous larvae will also augment that of the native insect and microarthropod soil fauna. We discuss the potential new synergy between this functional group and that of a number of established non-native plants, reliant on insect pollinators for successful seed-set and hence dispersal, that are currently of persistent status with very limited local distributions.