Which category of flies is generally NOT considered to have significant medical importance?

Fruit flies are generally not considered to have significant medical importance because they are primarily associated with the fermentation of fruits and other organic materials rather than being direct vectors of human diseases. These insects are more of a nuisance in kitchens and gardens due to their rapid breeding and association with spoiled or overripe produce.

In contrast, house flies are known to be carriers of various pathogens that can lead to diseases in both humans and animals, making them medically significant. Stable flies are also vectors for diseases, particularly in livestock. Black flies are notorious for their bites and can transmit diseases in certain regions, further reinforcing their medical importance. Therefore, fruit flies stand apart in this context, as their role does not extend to health risks like the other mentioned categories.