Morphological characterization of the antennal lobes in the Mediterranean fruit fly Ceratitis capitata.

The medfly Ceratitis capitata is one of the most important pests for horticulture worldwide. The knowledge about anatomy and function of the medfly olfactory system is still limited. The first brain structure to process olfactory information in insects is the antennal lobe (AL), which is composed of its functional and morphological units, the olfactory glomeruli. Here, we present a morphological three-dimensional reconstruction of AL glomeruli in adult brains. We used unilateral antennal backfills of olfactory receptor neurons (ORNs) with neural tracers, revealing the AL structure. We recorded confocal stacks acquired from whole-mount specimens, and analyzed them with the software AMIRA. The ALs in C. capitata are organized in glomeruli which are more tightly packed in the anterior part than the posterior one. Axons of ORNs bilaterally connect the ALs through a commissure between the two ALs. This commissure is formed by several distinct fascicles. Contralateral dye transfer suggests the presence of gap junctions connecting ORNs from both antennae. There was no statistical difference between the average volumes of female ALs (204,166 ± 12,554 μm(3)) and of male ALs (190,287 ± 11,823 μm(3)). In most specimens, we counted 53 glomeruli in each AL, seven of which were sexually dimorphic in size.