Heya Snowman,
I've been lurkin' and learnin' for awhile now and I was gonna play it incognito for a bit longer but I just had to come in and post a reply. At first I was thinking, "hey cool, I wonder if any other nutrients would work?"
Unlike some flies, white flies don't lay their eggs in water, so they wouldn't be interested in it for that reason (and certainly not prone to drowning if it's a requirement of their life cycle). So we can rule that out as the attraction.
I'm not sure if white flies like to drink liquid water (anyone know?) but they might be attracted to certain scents in the impure water. It wouldn't be a big stretch to hypothesize that some of the same things that tells them a plant is a food source are present in plant fertilizers. I dunno, I've never used MG Bloom Booster so I don't know what it smells like (or, more importantly, what it smells like if you're a white fly).
The big worry for me would be that leaving out something that flies are interested in might attract more flies or other insects that otherwise wouldn't notice my garden. Granted, once you've got an infestation you might resort to methods you wouldn't otherwise consider, but I'd think that just a fly strip of some kind would work equally well.
White flies are also attracted to various shades of yellow. Was the liquid yellowish by any chance? (That's the reason they make the fly strips yellow, btw.)
Oh, and just so you know, I bet that MG wouldn't want people spreading rumors that their ferts double as pesticides. The regulation on pesticides is friggin' psycho, it could theoretically create a huge legal nightmare for them. Not that a couple people on a board would really get the EPA's notice or anything, just sayin' - they'd probably rather no one raised the question. Lots of stuff kills lots of stuff. Pure water will kill practically anything if you give 'em too much of it.
So long story short (too late, I know) I'm thinking that practically anything that'd qualify as plant food probably would kill most insects if they tried to swim in it for very long. On the flip side, anything that attracts insects probably shouldn't be left around places you don't want insects. Who knows what else you might get interested.
Personally I'd stick with traps or (even more ideally) predatory insects, though that's not really a great option indoors. Maybe some natural insecticides if you have to. (Not the evil chemical stuff that bends DNA and crap.)
EDIT: Just thought of something - maybe some spiders or praying mantises (manti?) would be good - they wouldn't be very problematic... well the spiders might be annoying if they build webs in your plants, but...
... any comments?
