We have lots of large twisted galls on our lombardy poplar trees' leaf stems. I've heard that twisted galls on poplar trees are not a threat to the tree. So, I'm not worried about them killing the trees or anything.
Do the galls in the fallen leaves contain insects or their eggs that will promote more galls in future generations? Will picking up the leaves help to reduce the problem the next year?
I looked inside a gall, and found that it appeared to be full of some powdery fungus or something. Is that normal? Was it really fungus? Could the insects causing the galls be attracting other pests or diseases to my yard? I hear the things that cause twisted galls are related to aphids, and we have a big aphid problem. It could be a coincidence, but I thought I'd ask, just in case.
Last year, our poplar trees were covered in what looked like house flies (and this was rather disturbing), but after some research, I think they were a certain kind of fly that eats whatever causes the galls. There aren't as many flies this year, but there are even more galls (and there were a lot last year). I've heard that they are supposed to be less frequent after a severe year. This does not seem to have been the case, so far. I'm kind of concerned that the contents of the galls could be bad for the yard, or my health. I've heard about tree fungi causing issues in the past.