Some neighbours in our common building put the water-pipes of their air-conditioning systems over the garden. The water drips from the pipes and creates puddles in the garden. There are plants growing nearby, but still there is sufficient water in the puddles to attract musquitos, bees and other insects. These are quite a nuisance to the other neighbours. We asked the neighbours to direct their pipes to somewhere else, but they didn't want to. Is there anything we can do in order to prevent insects from coming to the water puddles?
Since we're dealing with a small puddle from an AC unit, I think the problem here is just the force of impact from the fall always hitting one small spot. When the water from the unit falls down is splashes soil away and slowly cuts a place the water can collect into the soil beneath it. If the water weren't falling directly on the soil underneath it, your problem would be solved.
I'm going to suggest a Downspout Splash Guard. They're pretty cheaply available from most home improvement stores, just smooth out the soil where the puddle forms, then place the splash guard under the pipes. The splash guard will prevent the drainage from cutting a hole in the soil and slow the water down enough that it just runs off gently into the garden/lawn. Like Bamboo says, the water itself might not be the healthiest thing for plants (pH issues, dissolved metals, etc) so keep an eye on the health of the nearby plants. If you prefer a more natural look I have achieved the same end result with a large flat rock. The main point is that the water hits something that isn't soil at the end of the long fall.
Assuming there is no solution such as that I ask about in my comment, the only thing I can think of is to attach rain barrels or water butts with lids to the outlet pipes so that the water collects in there and not on the ground. Whether you could use this condensate water on the garden for watering purposes is another matter - if the plants in the area where the puddles are collecting are still healthy, then it's likely okay to use the water from the rain barrels to water the garden with in order to dispose of it from time to time. I wouldn't risk using it to water vegetables or food plants generally though because it will be acidic and may contain trace elements such as copper and aluminium, possibly lead and zinc too, depending on whether there's any soldered joints in the system. If the plants in the surrounding area start looking sick, then I'd be concerned about what exactly is in the condensate dripping out.
I can't think of anything you could add to the puddles occasionally to deter insects.
Depending on how extensive these puddles are you could easily get a load of crushed gravel with the 'minus' fines. This compacts, fills the holes, no water will be able to sit. Have it unloaded somewhere convenient then just shovel a few shovel fulls into the dips. This will also stop the making of a hole because the water hits the stone first and gets spread in droplets. Easy to walk upon. Wouldn't worry about using it for watering unless you've a few other friends that live in this apartment complex. The water barrels are a bit of work.
Another very very cheap easy thing to do if the only thing you worry about are mosquitos is to add a drop or two of chlorine bleach to the puddles. This vaporizes quite quickly, a tiny bit works well and won't be around after a day or two.