Hi. I'll start by saying that I'm brand new to the forum and I'm definitely no expert. I have been raising Monarchs for 3 years, now.
The first year, we had some success, but we had many deaths. I would bring caterpillars in, as soon as I saw them. One problem may have been that the place I was purchasing my plants from may have used pesticides. Also, some were probably parasitized.
The next year, I began bringing them in as eggs, preferably as soon as they'd been layed. If I see a butterfly ovipositing in the backyard, I go bring that part of the leaf in, immediately. I also would spray my Monarch eggs with the disinfectant Live Monarch sells. I had much more success that year.
This last year I haven't had much in the way of Monarchs. I've wondered if the hurricanes didn't effect their course a little. I had stopped using the disinfectant, as I don't know if it can go bad. I used it a few times at the beginning of the year and some cats didn't survive. May have nothing to do with that, but I didn't want to risk it.
So, what I can recommend is make sure that your plants are completely clean of anything that might be killing the cats. This includes any spraying that might be happening for mosquitoes and such. Protect them as much as you can. And, bring in those eggs, ASAP. If I'm right there to take an egg, the minute it's on the leaf, there isn't time for it to become parasitized. See if you have better success by raising from egg. I have 8 right now that should be emerging tomorrow. Then the fun will begin again. I also have 2 Pipevine Swallowtail and 8 Black Swallowtail chrysalids that seem to be in diapause. It's been 2 months for the Pipevines and 4 for the Blacks, but I've been told they can be dormant for an entire year, so maybe they'll emerge next year.
Oh, and I did have one Black Swallowtail and one Monarch this year that both began to pupate and died in that inbetween stage. The Monarch split the skin halfway up and stopped, so the skin was still there and visible and the bottom part was the green of the chrysalis. Sad, but very timely, as I was teaching a class to some second graders the next day. That had never happened before, so it was great, if it had to happen, it did it and I used it for education.
If you want to see how we started with butterflies, you can check out my website at www.pumpkinsandpets.com
It's a mess right now, as my friend is redoing it for me, but she had a baby, so it's on hold. Just scroll to the bottom and click on the butterfly link. Lots of pictures.
TTYL and good luck!