Olfactory sensory neurons (OSNs) detect odours at a wide range of intensities. In insects, volatile compounds are perceived by odorant receptors (ORs), which are made up of an odour-specific protein (OrX) and the ubiquitous odorant co-receptor Orco. In principle, ORs tune the sensitivity of odour detection, with some OSNs exhibiting exceptionally high sensitivity. To test whether additional mechanisms underlie odour-specific neuronal processing, we investigated synapses between OSNs and projection neurons in the antennal lobe, the first relay station of the olfactory pathway. Here, we studied the molecular structure and plasticity of the presynaptic active zone (AZ), the specialized site of neurotransmitter release. We focused on a highly sensitive OSN type that expresses the receptor Or56a and exclusively detects geosmin, an odorant signaling ecologically harmful stimuli. Using confocal microscopy, our results uncover a differential arrangement of the AZ proteins Bruchpilot (Brp) and Unc13A at Or56a and conventional OSNs. Interestingly, our investigations also show that Or56a-OSNs display a limited capacity to undergo homeostatic plasticity in response to a genetic reduction of presynaptic release probability. We hypothesise that this difference to conventional OSNs reflects the basal tuning of geosmin-sensing neurons towards maximum levels of performance.