

Explosions force burrowers to un-burrow, including plasma explosions and stuns (although I’ve had mixed successes with the latter).
The burrower warriors (= the red bugs) have medium armor (or pen3) on their faces, I don’t remember if the Helldivers Mobilize warbond has a pen3 primary but if it does, try that one; otherwise, you can use the MG or the HMG, among other support weapons.
Other than that, it depends on the warbonds you’ve got so far; what have you got so far?
In that case if you specifically want to build up for the burrower strain missions, you should get the Democratic Detonation warbond as your first warbond (besides, 95% of the playerbase says it’s the best one).
It has a grenade pistol with 6+1 shots, which is generally kinda weak (imo), but it can destroy holes/fabs/ships AND poke burrowers, as long as you can hit the ground without the grenade bouncing away.
If a secondary is not enough for you, it has a mini-rocket primary with heavy penetration and shrapnel, and an explosive crossbow with comparable damage but medium pen; the former hits hard (bugs and helldivers alike), the latter is one-handed and you can expect to survive when using it in CQC. Kind of.