Why aren’t hoverflies declining like bees?
Hoverflies, like many insect groups, do seem to be declining, but they are not faring as badly as bees in general, and a greater proportion of hoverfly species are thriving. The adults of both groups are nectarfeeding pollinators, which could leave them vulnerable to similar dangers such as pesticides and declining floral diversity. But there are also important differences. The larvae of hoverflies, unlike those of bees, tend to be predators or scavengers, which makes them less dependent on flowers, and perhaps less exposed to insecticides. Meanwhile, adult hoverflies tend to be generalist while bees are more specialised. This means they are better able to switch habitats or food sources if necessary, and because they are not tied to a hive, they can disperse more easily.
If you had to choose, best be a hoverfly (here a marmalade) than a bee.