Most Drosera tolerate immersion for a few days, a few are practically semi-aquatic at times. Almost all of the petiolaris complex grow in waterlogged, flooded conditions during the rainy growing season. It is believed that the "wool" on these plants is there to help trap moisture.
This complex and your species has been in wide spread cultivation for only 10 years or so and is unlikely to have lost any characteristics that ensure its survival in so short a time. Even with artifical selective breeding techniques it normally takes many decades of artifical selection to change such characteristics. That's why we still have VFTs that require dormancy and strong light levels.
If the plant is dormant I may not consider flooding.
Your choices for pest control are:
Manual removal - requires a lot of work and diligence as you have to cover a couple of generations. Effectiveness depends on your diligence and patience. Drawbacks - takes time involving active participation.
Chemical - effectiveness depends on proper application of the chemicals, selecting the proper chemicals and how resistant the pest is to the chemicals - drawbacks: kills other insects not just pests, plants can react badly to the chemicals or pests can be or become resistant. Drosera in general are sensitive to sprays and it is best to use a soil drench systemic pesticide.
Biological - predatory species mainly such as ladybugs. Can be effective but usually only will control (reduce but not eliminate) the pests. The problem is keeping the control species around or alive as the pest population declines. The control species may die/leave before the next generation of pests arrive. Drawbacks: can be very expensive for only a few plants, plus you have to put up with the predators wandering around and as noted before usually only controls, not eliminate the pest.
Flooding/Immersion - can be very effective drowning adults, pupae (depends on species of pest) and eggs all at the same time. Drawbacks - kills beneficial non-aquatic insects, a few species/vars such as Drosera filiformis var tracyii are not tolerant of waterlogged, overly wet conditions care should be taken to supply plenty of air circulation after immersion or immersion is to be avoided.
Manual removal is perfectly fine if you have the time and patience to do a thorough job. One of Joseph Clemens preferred methods of manual removal is to use needle spray from a spray bottle, tweezers, a small paintbrush and magnification. You don't normally find that in natural environs any where.
See also these threads:
http://www.terraforums.com/forums/showthread.php?t=110552
http://www.terraforums.com/forums/showthread.php?t=110728
And this web page on
Aphids