Pawpaw cultivars tend to be grown for desirable fruit traits (reduced seed, pulp flavor, yield of fruit quantity or weight, etc.) rather than how readily they tend to produce fruit overall. That is to say, they all (straight species and cultivars) depend on pollination every spring, and some years the insects responsible will have a good season pollinating and some years they will not, like if it's too cool and rainy, or if a late frost injures the flowers.

Pawpaw does need cross-pollination, as single trees rarely can self-pollinate to fruit by themselves, and any tree that is genetically different (so, not a sucker off the same plant, but a separate individual seedling or cultivar) can serve as the pollinator. We're not quite certain what insects are the primary pollinators for pawpaw. For that type of flower (smelling a bit like rotting meat, and also having that general color), which is found in a few other native woodland flowers, the pollinators include flies and beetles. We have read one reference that suspects scorpionflies can pollinate pawpaw flowers.

While native to understory conditions in the wild, in cultivation, pawpaw can be grown in nearly full sun and fruit more heavily as a result, though that is not a requirement. The trees you've seen in the woods could be a colony of suckers (quite common), which means they are all the same tree, genetically, and incapable of pollinating itself. Or, they are just experiencing the same uncooperative pollination conditions this year and may fruit well another year.

Miri

Thank you for the thorough response Miri! Very interesting-I love this small tree and the flowers are so unusual. Tried pawpaw once and it was so delicious. Even if it does not fruit I get zebra swallowtails in the garden and want to keep them coming. They bring me happiness.

You're welcome!