WMDs IN SPACE

[Dangerious P. Cats]

For a otherwise realistic(ish) space campaign I'm trying to find ways to elimernate weapons of mass destruction. The campaign is based around a war between Earth's Empire and a mostly unknown alien speicies where battles are mainly conducted in space (nearly all human military recruits are trained as pilots except for special forces units and are hence pretty much storm troopers in a ground war), with some planatry ground fighting. Part of the campaign theme wise is that the Earth Empire is evil and the players are effectivly playing storm troopers meaning that there are few rational reasons why thye wouldn't used weapons of mass destruction if they had them, they just don't.

So far here's my thinking:

Nukes: One of the core bits of the setting is that earth's resources have been thougherly used up, including all it's urainium resources, making the manufacture of nuclear weapons unviable. Any remaining nukes (if they exist at all) would be kept in reserve of the defence of earth.

Bactiria and virus: The enemy is a realitivly unknown alien spcieies (o.k, the big surprise twist of the campaign is that the enemy they're fighting are humans from another planet far away who speak a compleatly different language, but the Earth Empire doesn't know that) and therefore presumably hard to develope a desease to kill since little about their biology is known, meaning bio-weapons are not viable.

I'm less sure about other weapons of mass destruction, any ideas are welcome, as a rae comments on the ideas above.