defence against (annoying) dread lords

It is a question of your tech level. If you managed to equip your ships with a defence of a similar magnitude as the dread lord attack power (say > 30%) AND have enough hit points, so that your ship is not destroyed by the remainig attack power (<70%) by the first shoot, AND managed to load enough weapons to destroy the dread lord you shoud do.

But this is hard. The first dread lord frigate I ever seen has 522att.

Well my defense is a lot simpler.

Just have enough people living on the planet to withstand the invasion. They send roughly 20 soldiers they do an enormus amount of damage but if you have atleast 8000 or more living on the planet you can survive the first wave and shoot back. Needless to say that if 1500 morning widows shoot back the invader is repeld!

Also if you dont have enough but do have a transport ship leave the planet just before its invaded and return with the lucky souls that escaped the sloughter. Most of the time 1000 or 2000 soldiers in an invasion of a just conqured planed by the dreadlords can be taken back. In the proces u also get some nice tech none of the other races has.

You do need to have a high birth rate if you can't match their ships strenght soon. (stolen tech is a must in this)

hope it helps
Marloc

Yes, as others said, defenses against Dread Lords aren't really worth until you get closer to their tech level. Here's a few ideas that work well against them (at least in the campaign missions, I haven't tried the "Dread Lords on Parade" Scenario yet)

1) use fleets of tiny or small ships with no defense and do everything you can to make sure they are the ones that start a battle (get the first shot). The idea here is to completely destroy the Dread Lord ship in the first round before they can fire back. Or, if they do survive, most of their returning fire will be wasted against such a small ship (doing 40 damage to a ship with 6 hit points is a tad overkill).
2) use military starbases to boost the attack power of your small ships. Since you can have more of them in a fleet, the fleet benefits more from the attack bonuses of the starbase (which is per ship). Make sure you put the actual starbase a little ways back from your front lines though, because it won't survive an attack from Dread Lord ships.
3) Make use of cargo hulls with lots of engines, sensors, and one weapon. The idea here is to locate their transport ships and destroy them before they get to your planets (might not work as well now that 1.1s out, since the AI seems a bit better at escorting transports now).
4) This is kind of the opposite of #3. Let the Dread Lords take one of your planets. Have a transport nearby (preferably with a lot of speed) to retake on the next turn. Chances are, you'll get some technology by doing this (hopefully one of the high-end weapons). Fly all but one of your citizens out of the planet and let the Dread Lords retake it. Repeat ...