Insect Swarm is a very specialized plasmid: it is specifically designed to weaken and kill everyone in a given area. In short, it is a room-clearing plasmid which can also be used to momentarily distract foes. My upgrade tree both follows and expands on the original idea.
Insect Swarm 2 Upgrade #1: Superswarm. Swarm can split into two and attack two different targets at once. Unlocks Insect Swarm 3 upgrades #1 and #2.
Insect Swarm 2 Upgrade #2: Neurotoxin. Swarmed enemies have their aim severely decreased for the duration of the swarm. Unlocks Insect Swarm upgrades #3 and #4.
Insect Swarm 3 Upgrade #1: Corpse Hive. Enemies killed by the swarm will release another if an enemy steps on them.
Insect Swarm 3 Upgrade #2: Seeker Swarms. Swarm will not die until it has found an enemy, and will patrol the level. Upon finding an enemy, the victim will be highlighted in yellow and will be visible through walls.
Insect Swarm 3 Upgrade #3: Healing Hornets. Part of the damage dealt by the swarm is also converted into added health for the player.
Insect Swarm 3 Upgrade #4: Plague. Each time a swarmed enemy is killed, the swarm will receive an increased lifespan and will move on to the next enemy.
For once, I have all the icons. I still want your opinion, though.