Dark green nectar glands arranged in a circle at the base of an Oscularia deltoides flower produce the tasty enticement for ensuring flower visits from the plant's designated pollinators. Such species designations are only manifested in the tastes that have been acquired and reinforced over numerous generations, ensuring that certain insects will keep responding instinctively to “the right” flowers.
Most flowers without their insects would be doomed to extinction from the absence of seed; most insects without their flowers would die of hunger and disappear. But birds and even mammals (like small rodents) also perform pollination services for certain flowering plants; nature does spread risk. And then there are the less socially inclined flower species that self-pollinate, saving themselves the trouble of nectar production.
Some kinds of flowers are pollinated by nearly everybody (not counting everybody’s dog). As long as the everybody can move about, needs to eat, can identify the flower as a food source and has an appetite for the nectar on offer... dogs clearly wouldn't feature. Other plants have “agreements” varying in specific exclusivity, not bothering with spreading their risk.
The extreme case would be a plant being fully dependent on only one specific pollinator; in the absence of which it would be thwarted in its quest for viable seed. The converse is then an insect needing its diet from just one plant species. Such a plant would have to perform through every season of the year, unless the insect morphs into a non-feeding stage during some seasons; the animal hibernates.
Many figs are in such singular mutual relationships with specific wasps. Only the wasp larva eats fig though, the wasp flies about having other options. Mobility would be wasted on a species that gains no survival opportunities from walking, running, climbing, slithering, flying, wading or swimming (Smith et al, 1998).