Help with Fungus Flies (help!)

About 2 1/2 years ago we had an infestation of what I was told (by an exterminator) were fungus gnats/flies. We had a leaky pipe in the ceiling of our basement (partially finished basement). Pipe was replaced and bugs were treated but the problem never really went away. Multiple exterminators have been to my house over the past 2 years. I open the basement wall (it was drywall/plaster over brick) and found lots of bugs. This wall was below the original leaky pipe. They were treated with multiple applications and the problem seemed to go away (from December to March they largely disappear).

Early this year we had a sewer back up and we discovered the the pipe that comes from our upstairs kitchen sink had a broken in the floor of the basement. this likely had occurred years ago when a french drain was installed. The pipe was dug up (lots of dirt was removed and the ground was treated. Bugs have largely been gone but have suddenly returned over the past 3 weeks. We are also getting them on the other side of our basement as well (unfinished side f the basement). Our basement is not very damp and we run a dehumidifier daily.

My theory is that our french drain is the source of the problem (since we have the bugs on both sides of the basement and the french drain is internal and goes around the entire basement. The weird thing is that we really don't see any bugs from December - March/April - this year very few until late June. Are these bugs getting in from outside? should I try to have my french drain flushed? I really would appreciate some guidance.

Also - I live in Pittsburgh, PA.

 

I doubt the source is from the exterior. Even if there was a source outside such as manure pits, stagnant pools of water, etc they still don't want to invade a structure. Wherever we see them, I'm confident that the source is nearby. Since you've dealt with the original problems, I'm thinking this is a new problem and possibly the french drain is the source. I don't understand french drains completely and I suspect that they differ in how they remove water.

I can only speculate as to why you don't see them in the winter; a possibility is that the temperature where they are breeding drops just enough to slow/stop gestation but spring/summer bring it back up.

Does the french drain empty into a sump where there is a pump that takes it somewhere outside?

Maybe it simply drains/stays under the house slab?

The answers could lead us to an insecticide treatment, or possibly prohibit the same.

 

Thank you for your reply. The sum pump pumps the water outside and empties into the yard a good 20 feet from the house. The sum pump almost never runs - I suspect the French drains were poorly installed. They are basically a plastic pipe that goes all along the inside wall of our basement. Our basement gets very little water to begin with. Could it be possibly that “food” and other “junk” got into the French drain from the leaky sewer line/garbage disposal and the bugs are feeding off the same mess in different areas of the French drain? Maybe that sounds crazy. I have been dealing with this so long it might be making me crazy! Should I try to flush the French drain? Not even sure that is possible.

when I check out the sum pump pit (where it pumps the water out) I never ever see bugs. Just along the bottom of the wall at a few points in the basement (and near windows). I usually catch about 10-15 a day on sticky paper I have with a bug light. It is so frustrating.