Some species of flies and mosquitoes are also pollinators. One cute example of pollinating flies are the Bombyliidae. Mosquito larvae are also important food sources for aquatic and semi-aquatic species like frogs and fish.

If you study wasps, you'll find that they very frequently have odd symbioses from species to species, most often as parasites/parasitoids or hyperparasites. Some even have symbiotic relationships with viruses that assist them in their parasitism - ichneumon and braconid wasps have symbiotic viruses called polydnaviruses.

Haha there's a reason why the Xenomorph from Alien is in part inspired by parasitoid wasps.