Only bug types, eh? Well... You're forgetting something, I should think!

Parasect VS Kadabra
Kadabra is handily spooked out of the gym.
Magneton VS Mr. Mime
Now, a mythology lesson for you. Fae don't really like cold iron. That goes for things both dormant and moving in to body slam you.
Arcanine VS Jynx
Jynx becomes... Blacker. Hair-wise and clothes-wise.
Raichu VS Slowbro
Slowbro's forced out of their shell with a jolt.
Result: Who says we need a lot of bugs? Just abuse their other type!