These are Oriental Fruit Flies. Fruit tree growers and most farmers are very familiar with these insects or, most would say, "pests". Organic farmers use pheromones placed inside traps to attract and confine them. The pheromone contains methyl eugenol as active ingredient. This mimics the scent of female fruit flies thus attracting the males.
But why are these fruit flies gathering around this plant? This plant contains methyl eugenol. This plant is very common, its a basil.