When I get little ~nats in the dirt of my house plants, I water the plant using soapy water. The soap bubbles/foam on the top of the dirt, smoothers then and the die. Do this several times (~once or twice a day) til they all die. To avoid watering a plant too much, I'll make soapy water in a bowl and just skim off the foam w/ my hand and wipe it on the dirt.