I can see this as being an interesting weapon, and it has its pros with its use. However, there are also (as with most things) cons.
Pros:
For one, a swarm of killer wasps is difficult to fight off. In many video games and books centered in the dystopian genre, swarms of murderous insects are used quite often for this very reason. You can shoot at the swarm all you want, but there are always too many for a few pathetic bullets to do enough damage. You can attempt cutting at them with a sharp weapon or go on a desperate attempt of bug-spraying the air, but more often than not even that won't do any good against genetically modified bugs. The fact that a swarm is so hard to defeat is a major pro to any government or military force using such tactics.
Another pro would be the fact that the swarm of wasps (assuming they can be controlled by whoever is using them) is controllable. Nukes, explosives, and weapons of mass destruction cause accidents, you can't tell an explosive what its target is or what it is not supposed to harm, its only task is to harm anything around it and blow it to smithereens, friend or foe. Assuming the wasps are genetically modified to do so, a swarm of killer wasps has more practicality in this way. Someone can tell them exactly what the target is, and they will only attack the one target, taking no accidental collateral damage on an ally that just happened to be in the wrong place at the wrong time. They could potentially be able to recognize who is the enemy and who is not, and hence their attacks would be much more precise, potentially taking out the risk of harming your own allies.
The idea of a swarm of wasps can be lethal. Just because they seem pretty harmless now in the real world, considering they are only about the length of your pinkie finger and cause relatively little pain, doesn't mean they have to be harmless in your story. Give their venom a kick to it, in the Hunger Games a wasp like creature called <PERSON> could send you into a delusional frenzy if you were stung by one. Why not have yours do something similar? Maybe being stung by one means certain, painful death, maybe instant death, maybe it forces you to see the thing you are most afraid of (give it a bit of a Scarecrow from the DC franchise vibe) or maybe it sends you so insane you feel a giant, uncontrollable urge to kill everyone you love, or maybe you turn into one (more far-fetched, but still doable depending on what your story is like). Even better, give your swarm of wasps size. Why not make them the size of a human... or bigger? The only issue there is they would be easier to shoot at and kill, however also more overwhelming upon attack, so there is a pro and con in that change. 238
Or you could keep them tiny. Tiny can be deadly too.
Cons:
If this is modern warfare as in 2000s contemporary, a swarm of wasps as a weapon is going to be difficult to pull off. People can see that happening in dystopian or sci-fi novels, but if this is contemporary people won't believe your story. In today's day and age, the technology to pull something like making genetically modified and mentally controlled swarms of killer wasps is... non-existent, to say the least. Besides that, governments wouldn't fund such a project, not now anyways. The money for it would certainly be off-the-charts, not to mention the idea now would seem ridiculous to government leaders. Maybe in the future when the technology is around (or if your novel is contemporary science fiction, but if it's just contemporary... most likely the idea is going to be shunned, both by characters and the audience.
Wasps are killable. I stated before that a swarm of them would be difficult to kill (and that comment still stands), however they are, eventually, killable and destructible. They aren't metal, so certain things are going to wound them that would have no effect on, say, a tank. On the Swarm vs Explosives point you brought up, explosives don't get wounded. They wouldn't physically get hurt and then go into survival mode with the possibility of retreat because they don't think, they are simply explosives and that is what they will do one way or another: explode. Wasps on the other hand still have instincts. They will get hurt and possibly die (although with a swarm of them even if a few die there is no real damage done other than loosing "troops," with victory sill a possibility of the high 90 percentile. However because they are creatures, genetically modified or otherwise, survival instincts are still in tact. If a lot of them, in some way, were to get wounded, there is a high chance the rest would retreat, simply out of survival instincts. 238