Can ant colonies reproduce and sustain with no queen? And what is the role of the queen in the actions of the other ants? Has it been found to have any instruction, or only egg laying? (Angela, Baton Rouge, Lousiana, USA)
In a "typical" ant colony, there is one or several queens that have been fertilized on their mating flight before colony founding. These queens lay eggs. The queen can lay fertilized eggs, which will develop into females (workers or - when the colony is mature - workers and new founding queens). The queen can also lay unfertilized eggs, which then develop into males. If there is only one queen per colony and this queen dies, the workers can start to lay eggs. But since the workers have not been fertilized, these eggs only develop into males. Males don't contribute to maintaining the colony, they will fly off once mature to mate. So the "typical" colony cannot sustain without the queen. However, there are some ant species (e.g., Platythyrea punctata), in which workers are clonal and lay eggs that develop into females. In these colonies, the most dominant worker will lay eggs while the others maintain the colony. Once this reproductive worker gets weaker or dies, another worker will become the reproductive. A really nice review on exceptional colony structures is "The demise of the standard ant" by Jürgen Heinze.
Coming to your second question: Ants communicate with chemical signals. These can be pheromones or cuticular hydrocarbons. The queen produces a range of pheromones and by this gives instructions to her workers. One important instruction is that the workers don't lay eggs. It is in the queen's interests that she is the only egg-layer and the workers nurse her offspring, forage and defend the colony. So the queen produces pheromones that suppress the ovary development of the workers. Once the queen dies, the workers will start to develop ovaries to lay unfertilized eggs and these will develop into males. Please also read this post on ant pheromones.
All the best,
Steffi Kautz & the AntAsk Team