Fed up with rose slugs

I've had it. After nearly 2 weeks of squashing bristly rose slugs on the rose bushes every singly day, I can't take it anymore. One time I found 5 of them on a single leaf - they were extremely small and must have just hatched. When were the eggs laid?? I'd like to have a "chat" with the mother sawflies (the bristly rose slugs adult stage of life). They just keep coming and it's driving me nuts. An article on the subject by Fine Gardening Magazine says:

Depending on the species, there can be one to many generations each year -- one for the European rose slug, at least two for the curled rose slug, and six for the bristly rose slug. 

Six?! So does this mean that they lay eggs six times throughout the year? A month? I don't quite understand, but it doesn't sound very exciting to me either way.

So, naturally, it's time for a new battle plan. One of the "solutions" for fending off the rose slugs that I found on a forum suggested sprinkling flour on the leaves of the plant and then rising it off after 24 hours. Information on this approach is basically non-existent and I saw several posts of people saying they would try it and report back, but never did. I only found one person who actually claimed it worked. And apparently, that's enough for me, or maybe I'm just a little crazy, but I decided to do a little experiment to see for myself if it works. So, I did.

On Wednesday, I took the bin of flour outside and threw it all over the all three rose bushes (both the tops of the leaves and I also tried to throw it up from a low position to get underneath them as well).

Rose bush covered with flour

Then the next day I hosed them off (the flour was surprisingly difficult to get off)...

So, did it work? I did a quick hunt today to see if I could find any. I only searched the new rose bush and found...... two of them - largeish ones:

Large bristly rose slugs

I couldn't notice from a distance, but while taking photos of them, I realized that they were actually still munching on the leafs even after I pulled them off! It turned out to actually be rather interesting to observe, so I also took some video:

I'd say I caught them in the act! Just watching the video makes me feel angry...

It is worthy to note that I didn't find any small ones, which is typically what I have been finding lately. These two must have evaded my previous hunts. It's possible that these two were large enough to be able to survive the "flour attack", while the small ones can't? It's hard to say, because I have no idea how throwing flour all over a plant is supposed to get rid of these things, but I also don't really care as long as it works.

So, the final verdict is still out. I'll see if any more show up in the coming days.