I am surprised in this tread that insectivorous plants have not been mentioned earlier. A local small specialist nursery close to my home that uses bark based compost for permanent pot grown stock, but peat based for other spring propagation plants relies almost solely on pinguicula plants placed every yard or two throughout the greenhouse, and has done so for many years. The larger fleshy leaved P. caudata types work best but other species are also used, and give a change of flower colours. I would have thought that the sticky plastic traps similarly placed would be as effective, but not so appealing. Peat is only a minor part of my growing composts, as I use various mixes of soil, commercial soil based compost, grit and composted bark as the major growing medium, so only odd plants suffer from gnats, and sticky traps seem to mop up them. Brian Whyer, zone 8'ish, Buckinghamshire, England