Fruit flies or fungus gnats

(Question)

I live in Manitoba ( zone 3 ) and I have three potted plants ( Hibiscus, Holly and Norfolk Pine ) which were on my deck all summer and have now brought in for the winter. Since bringing them in the house I have noticed a lot of tiny insects like fruit flies flying around. Could they have come in in the soil and if so, how can I get rid of them? Is there some kind of insecticide to put in the soil.

(Answer)

As a rule of thumb its a good idea to douse plants that have spent the summer outdoors with insecticidal soap before bringing indoors. The most likely culprits you are seeing are fungus gnats. They are small, slender, dark insects that fly around when plants are disturbed. While the adult flies are annoying it is the larvae which may cause problems. The adults lay their eggs in soil that contains decaying organic material.  Larvae, particularly if a large number are found in the soil, may cause root damage or stunted growth.   Let your potting mix dry more between waterings as larvae cannot survive in dry soil. Try catching adults by placing yellow sticky traps in the soil. Hope this helps.

For more detailed information go to:

https://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html