I released about 200-300 ladybugs into my greenhouse and they all got eaten, many went straight past the aphids, assassin bugs however and a different story, many of these walk straight over drosera and are smart enough to avoid nepenthes, however I'm not sure you can buy them.
Another method I use is white oil, it works well, doesn't seem to affect nepenthes or sarracenia and is cheap, you will have to use it once every 2-3days and for about a month or two (depending on how many there are), it also stops thrips and white fly, but drosera and pings hate the stuff, in my experience.