I also have experience of insect plague being reflected. It is a single target spell (albeit with area repercussions) and as such is susceptible to spell defenses. I dont use it very often because of the lengthy cast-time, so perhaps I am wrong.
Regardless - it is good practice to cast it on a secondary target, and let the insects pass to the intended caster, if you feel the target for the spell is less magic resistant.
Killing spell casters and monsters with spell ability
I did test it again. Not all insect spells are area spells. What you will have experienced will have been probably not an Insect Plague or Creeping Doom being reflected, but a "Summon Insects". Insect Plague and Creeping Doom are area spells. Summon Insects is a non-area spell, and thus subject to Spell Turning.