Mites and Nepenthes
So you've got some funky looking new leaf growth but the old growth seems healthy? Has your plant decided to activate a bunch of shoots along the stem? Well if you answer yes to both of these, chances are you have mites. The infection signs manifest themselves slightly differently across species. Hamata, tentaculata, glabrata, nigra and other Sulawesi affiliates are by far the most susceptible. Some Sumatran species like spathulata and jacquelineae can be very susceptible as well. Philippine species like ventricosa and sibuyanensis can also be affected but when they are attached the new growth points often are yellow and growth will cease.
Unfortunately, there's a lot of mite species out there that target plants. The most well known is the spider mite. These guys are larger in size than the other mites I'll describe. You'd still have a lot of trouble seeing them with the naked eye but under a magnifying glass or with a macro lens you'd definitely be able to make them out. They are red in color. Spider mites thrive when temperatures are warm (80+ degrees) and humidity is low. They dislike being sprayed with water and high humidity. I've found that for mild infections, it may be possible to simply change the environment and the spider mite problem can disappear.
There's other types of insidious mites out there. The worst of which are broad mites, cyclamen mites and tarsenoid mites. These little guys are impossible to see without a microscope. Even worse, they love humid, cool highland conditions just like the highland Nepenthes they infest. And to make these devilish things even more sinister... they burrow into the leaf making them harder to treat.
So how do we battle these nasty creatures?
First off, we need to understand the life cycle of these pests. Mites attack new growth but leave the older growth alone. Therefore, a plant with new growth under attack will often activate lower nodes. Left untreated, the new growth points will soon be attacked by mites as well and the cycle keeps on going. Mites lay their eggs immediately after they mature. The eggs take a few days to develop to instars and then a few more days to maturity. This presents a real problem for treating them with chemicals because there aren't any miticides out there (to my knowledge) which are either systematic or kill all life cycle stages. Therefore, you may need to treat multiple times at very specific intervals to eradicate the entire infestation. The treatment interval will depend on the type of mite you are fighting and likely the room temperature (which will affect the maturation time of the eggs and instars). It's best to figure out what type of mite you are battling and then read the miticide label to treat it accordingly. When in doubt, I've found a 6 or 7 day re-application period to do well. Be very diligent about this because unfortunately mites have an uncanny ability to evolve quickly. If you treat only once and some mites remain, you are effectively forcing survival of only the mites which are the most resistant to the treatment. Therefore, I often used multiple miticides in a cycle to ensure mites are completely eradicated.
In general, insecticides do not treat mites. The chemical used to target mites is called a miticide or acaricide. Insecticide does not equal miticide. Let me say this again for effect: insecticide != miticide. The vast majority of insecticides out there aren't intended to eradicate mites. Two exceptions that do treat some mites are bifenthrin (trade name Talstar Pro) and Spirotetramat (trade name Kantos). However, not all mites are targeted by these chemicals. I should note that in general, miticides are generally on the nastier side of horticultural chemicals so USE THE RECOMMENDED PERSONAL PROTECTIVE EQUIPMENT when applying and please follow the recommended restricted-entry interval (REI) before returning after application.
Unfortunately, miticides and many insecticides are usually more targeted for commercial growers. Even the smallest sizes available can be fairly expensive for the regular hobbyist and it is often a quantity so large that you'll use only a tiny fraction of the chemical before it expires. Even more unfortunate is that it's illegal to sell chemicals in smaller quantities than the manufacturer produces (so please don't ask me for this). However, I'll say this: the marijuana industry has revolutionized availability of many horticultural products that were once only accessible to commercial growers... and it's often on Ebay. I've seen people taking the risk of selling a bottle of Superthrive which includes a free small bottle of miticide. I don't fully the legality of this; however, I will say that I've bought from these sellers in the past (before I became a commercial nursery) and had good results. But buyer beware of course.
My first line of defense is a miticide called abermectin (trade name Avid). Used at label strength, I have not noticed a deleterious effect on Nepenthes. Although this miticide is not systematic, it is trans-laminar, meaning that if you spray one side of the leaf, in theory, it should also get pests feeding on the other side. Avid is the broadest spectrum miticide out there and is intended for use against nearly every type of mite that affects plants. It's also cheap and readily available compared to other miticides.
Another common miticide is Bifenazate (trade name Fluoromite). Though readily available compared to other miticides, it doesn't work on broad mites, cyclamen mites or tarsenoid mites. I've used this one without any deleterious effects to Nepenthes.
A relatively new miticide that is extremely effective against all mites is Spiromesifen (trade name Forbid 4F). The label on this states that it targets mites at younger life stages (not the adults) and that it is effective for 45 days. I've used this one without any deleterious effects to Nepenthes.
Another common miticide is Fenpyroximate (trade name Akari). This one is actually a combination miticide/insectide. I've used it before with no deleterious effects to Nepenthes. However, I don't think it was as effective as Forbid 4F or Avid and it was expensive.
Chlorfenapyr is another common miticide (trade name Pylon). It works against a broad range of mites. The liquid form is very expensive and I've never decided to make the investment. However, the most interesting product is the total release (TR) form of application. Essentially, it comes in a fogger container and once activated a fog spreads to fill the area of a standard commercial greenhouse (3000 sq ft). Once you open it, you cannot stop it so beware. Follow the label instructions about minimum distance away from plants. I don't know if you can overdose plants in a small greenhouse using one of these canisters since I've always used it in a larger greenhouse. However, I did do a test run of a tray of plants enclosed in a 14' x 7' trailer at one point. The plants showed no deleterious effects. I did lose one plant to overdose (a relatively large lowii x ephippiata). It was directly in front of a fan during the overnight application and the next day it had white residue all its leaves. The plant died a couple weeks after that. I've never relied solely on the total release to eradicate mite problems. Instead, I treated with other miticides and used the total release as a "clean up" to kill any residual mites I missed with the spray treatment.
For those that don't want to go the chemical route, there's alternative methods. For spider mites, a simple change to the environment (wetter and cooler) may eliminate problems. For broad/cyclamen/tarsenoid mites, sometimes the only way to eradicate them is the heat method...
For the brave, you can eradicate mites by submerging them completely in 110F/43.3C water for 30 minutes. The plants will not love this and may throw a fit for a couple months; however, I've never lost a single plant to this treatment and this includes really finicky small hairy red hamatas.
I've often had people ask me about more natural miticides like neem oil or other products like Bayer 3 in 1. Honestly, I've never tried these products. They may be worth a shot for a small collection. However, I'm generally of the opinion that trying to do too many things leads to few of the things being done well.
Also note that the same treatment methods described above are often used for whitefly and thrips.