Well-defined neural circuitries in the invertebrate nervous system have long served as model systems to address fundamental questions in neuroscience (Kandel, 2001;Masse et al., 2009). The insect antennal lobe (AL), in particular, possesses highly specialized and well-defined neural circuitries ideal for examination. In this review, we will assess how developmental processes in this brain region contribute to the evolution of sexually dimorphic pheromone circuitries within insects.Insect neurobiologists have long been fascinated by the curious anatomy of the AL, not only by its synaptic organization, but also by the functional properties of its neurons. Each AL neuron has a defined role in processing information. When combined, these neurons reconstruct the complex olfactory world of an insect (Hansson & Anton, 2000).