[Possum]

I've got a small, but rapidly increasing, attack of whitefly and blackfly in my polytunnel. I was thinking of hanging up some of those yellow sticky papers to trap them. Then I realised that, if they don't fly, it will make no difference. Does anyone know the answer?

[jaykay]

The adult females fly to find new plants, but once they've got a good host, they go into 'clone' production and produce lots of flightless babies.

So the traps don't really help once they've arrived.

Spraying the plants with a weak washing up liquid solution is as good as anything as it breaks down their waxy outsides and they dry out. Feels better than covering your food with insecticides.

[Fleecewife]

I detest those yellow sticky traps.  The only things I ever caught in them the one year I tried them was beneficial insects  .  It's impossible to rescue anything stuck there such as bees, hoverflies, lacewings - all the lovelies you want to encourage.  They stick on by their wings so can't come off.  Those horrible sticky things are banned from my garden 
 
As well as soapy water as Jaykay says, you can just squash them between your finger and thumb, the more the merrier - very satisfying  .  I get greenfly on my roses early in the year and squash the worst ones.  Some aphids are always left, but there need to be a few to feed the predators when they hatch.
 
Whitefly are different.  You could catch those with sticky traps held near the plant.  The white fly jump off the leaves (I think they are usually on the back) when disturbed, so if you do it several days running you might catch a fair load.  I've not had whitefly, but I don't think they do much harm.  But please don't leave the traps around between hunting sessions.

[Possum]

Ah! I always thought that sudsy water just washed them off. Now I know that it actually kills them I shall persevere with it.


Fleecewife - I share your concern about trapping beneficial insects but your suggestion to just use the sticky traps in short sessions is a good one. Will go and get some tomorrow and will see how I get on.

[Marlboro]

The only thing I caught in sticky traps was my hair. Squash the aphids with your fingers, if you leave a few it will encourage those things that eat them, if you don't like the feel a jet of water will wash them off, don't worry about getting them all.

[Possum]

Just an update. The yellow sticky sheets caught very few aphids, even though i was shaking the affected leaves fairly enthusiastically.   Fortunately, no beneficial insects have been caught. I am now spraying with sudsy water twice a day and it does seem to be controlling the little blighters.