The trapinch line, despite their insectoid appearances, do not actually exhibit any affinity for the bug element naturally, anonymous. (Or, well, vibrava is capable of learning Bug Buzz without assistance, but other than that, I mean.) Rather, the entire line exhibits a strong alignment with the ground-type at first, then with the dragon-type as it grows into its advanced stages. This goes for both its offensive and defensive capabilities. It’s not only true that members of the trapinch line are incapable of learning bug-type moves, but it’s also true that none of them display any of the weaknesses or resistances of a bug-type.
Remember, anonymous, a pokémon does not simply receive an elemental classification according to its physical appearance. What matters more is that pokémon are both capable of controlling a certain element and respond to other elements in a certain way.
The Pokédex According to Bill 