Gay fruit flies can be created by appropriately inserting the shibire gene. This will cause its neural chemistry to be heat sensitive. Above 30 degrees Centigrade its neurons will basically cease to function properly. It will then become insensitive to male pheromones which usually stop courting rituals. At even higher temperatures the receiving male won't even mind and will reciprocate the attention.
By having a box containing only males, a gay orgy will ensue. The males will link up to form chains and circles, in a display formation rarely seen outside of lesbian porn videos. The females can only look on forlonly, in a perfect reversal of human behaviour.