I agree with Gill, lots of pics are good!
BUT, in regards to what you have mentioned, it sounds like they are rotting on their own & possibly the bugs are making use of a good available home. (Possibly too much moisture, wrong conditions of some sort... heat + humidity is often good, but too much can do harm...you know, the common sense things.) Find a plant doing decent, & un-pot it carefully to have a lookie.
I am big on examining things when a plant goes bad, and try to find out exactly what is happening.
Anyone who's ever had a poor compost heap or a garden with the old tomatoes & veggys tilled in can attest to the vast array of bugs that are attracted to the stink of that mushy rotting flesh of all those vegetative remains. In fact, your description of the rhizomes reminds me of when I have picked up a tomato or peach from the ground, only to discover the bottom is rotted & gross, as I see a host of tiny beetles, ants & other bugs fleeing in escape. Yuck! But indeed, that is what I am reminded of.
Yes you want to get rid of the bugs, for they will cause problems themselves, but I am unsure if they are the cause of the problem instead of just a symptom.
The neem seems a reasonable start, although I am not fond of the oil all over. But I have used it for things like scale, mealy bugs & such with no bad effect on my plants. The oily residue isn't great, and I am not sure if it will be a problem if using it to soak the soil, but seeing as the plants are outdoors, I am sure it will wash away in time.
As for actually addressing the problem, I think more investigation is needed. Just my thoughts.
I thought root rot at first due to perhaps being too wet over the winter, but as more and more keep dying and I am not keeping them too wet, I just can't figure it out. If anything I keep them too dry. I've tried taking pics but can't get any to turn out. When I do an insect search the bugs just look like little black sugar ants.
Orthene wettable powder works well on Sarracenia. Neps too.
Flytraps... not so much.
Good suggestion on more insecticides.
I saw this online & thought it had some info on long term control, which seems the only way to deal with the problem.
Part of the pleasures of living in the colder climates, is that many of the insects & nasties
can't take the cold... although many can! Cold bad for the plants, but also many bugs!
Seems nowhere is ideal for everything!
Again, good luck.
From what little I have seen on 20 minutes on the net, it seems ants can be a long term problem that may have to be dealt with on an on-going basis.
Here's another insecticide post that may help:
White and fluffy parasites, ohno!
Last edited by GrowinOld; 06-02-2011 at 11:47 AM. Reason: addition
Grand Hotel... always the same. People come, people go. Nothing ever happens.