Are insects intermediate host or definitive host? are there any symptoms of gongylonemiasis? if the insects are the definitive host, would we see any clinical signs?

They are intermediate hosts.

Explanation:

Disease-transmitting insects are called vectors.

The life cycle of disease-causing pathogens is closely linked to the biology of the insect that carries it.

 The symptoms of gongylonemiasis include  hemorrhagic inflammation  at the site the pathogen invades,  followed by  granulomatous tissue development that  produces nodules in the invaded organ.

Some diseases transmitted by insects occur in both humans and other mammals because our differences in anatomy and physiology are not very different.

It is unlikely that clinical symptoms will occur in humans if the insect were the definitive host, because our biology is quite different from their biology, and the pathogen would be adapted to fulfill its entire life cycle in their body.