depends on what ant species, but one consideration is to elevate temperatures to match their natural disperal chronology...maybe even drench them a bit with water as some species use the temperature and a rain event to foster nuptial flights. Like I said, it depends on what species you have...good luck.

Dear James,

Many thanks, I have made "artificial rain" in the nests but yet no answer… Maybe I should lower temperature a bit before and then raise it again, I am not sure. The species for fire ants here is Solenopsis invicta.

Dear Dr Fox, I work with S. invicta and can get small colonies through artifical mating. Inducing and geting a mating flight is dificult for this ant. Females fly on sunny warm days high in the sky where they form swarns or a cloud high up in the sky and a half hour or so later males fly and mate. Hard to duplicate in a lab.   Brad Vinson

Getting a complete complement of ants in sufficient number can be a real challenge for any ant colony...S.invicta is no different.  I think given your conditions, you may just have to try to secure more colonies. I've collected S.invicta in the field quite a bit over the years, and have observed nuptial flights in lab colonies I've had...the only problem is that wasn't my focus or intent. So, all I can state there is it remains possible...nailing down how to artificially induce that is a whole different story.  This is why maybe one option is to simply attempt to collect more colonies to increase your chances...if that is even possible given your local considerations. Any chance of accessing monogyne vs polygyne colonies here? Likely a molecular diagnostic is out there that might provide some light there...just a thought.

Dear Dr Vinson, 

Many thanks for your insight. In Brazil I know that flights are rather desynchronised, and that colonies tend to produce either males or females for a flight event yet they eventually meet -- as a consequence seeing nuptial flights of fire ants is kind of rare there. In the US, I have been told (never collected there) that this synchronisation is much more marked, as you describe. I have observed one nuptial flight in the rearing room as soon as I arrived, thus now I know it can be done, though probably depends much on luck. I noticed that males attempt to fly rather easily, haven't seen gynes flying since that particular day…  

Dear Dr Austin,

Thanks much for 

(Warning: most of original answer disappeared upon posting thus it had to be reentered, in a summarised version!)

Dear Dr Austin,

Thanks much for your thoughts. We have both monogyne and polygyne colonies here. If people in the US have problems inducing nuptial flights, imagine here in Europe under artificial conditions. I was considering forcing the ants into mating by arousing males with cooling and then immobilising females -- any thoughts about that?

Thanks to all

You can get them to fly in a greenhouse but they don't mate under those conditions.

there is a paper on forced copulation that might be of use.  I have attached it here.