Neem Oil
Instead of systematic insecticides that may end up harming or damaging your sundews and carnivorous plants, I use Neem Oil. When I first had a fungus gnat outbreak on my Drosera adelae, I tried using an Earl May systematic insecticide powder. The plant died as a result. The next time, I had an outbreak, I used Neem oil. It managed to kill both the larvae and adults. Neem oil is a natural oil extracted from the Neem tree.You can find Neem Oil at Wal-Mart, and it is generally sold by the quart for about $12. Though it is a pain to buy in bulk, it will last you forever. Neem oil is very effective, although it smells a bit like rotten oranges.
The Neem solution (about 2 Tablespoons per gallon of water) can be poured directly in the soil or used as a foliar spray on leaves for mites and aphids. I have used doses MUCH higher than the recommendation and the plants have never been harmed at all. The label says that Neem oil is also an effective fungicide, but I haven't had to try that yet...
I have never had any problems using Neem Oil on my other carnivorous plants, such as Cephalotus, Nepenthes, Sarracenia, and Cobra Lilies (Darlingtonia californica).
Neem Oil also gets rid of Springtails and other tiny white bugs, which can become numerous in your sundew pots over time. Although they don't hurt the sundew, I generally try to get rid of them since I hate anything that crawls around in my pots.
Neem Oil has not worked for me on slugs or worms, so try another method if you have this problem.
Some systemic insecticides have been proven to work well, but be careful to not overdose, or the sundew could take a turn for the worse.
Neem Oil was recommended to me by Bill Matthews (WildBill is his forum name on www.terraforums.com), a member of the New England Carnivorous Society. He uses it every other week on his famous Cephalotus which have sold for 500+ dollars in auctions.
Remember that rinsing your media first will dramatically help reduce fungus and insect outbreaks.
Additional Questions or Suggestions?
Contact me at: sundewman(at)yahoo.com