A scanning electron microscope study of the antennal sensilla in adult Zygoptera

Scanning electron microscope studies of the antennal flagella of Coenagrion puella and Ischnura elegans (Coenagrionidae), Platycnemis pennipes (Platycnemididae), Lestes barbarus, L. viridis (Lestidae), Calopteryx virgo and C. haemorrhoidalis (Calopterygidae) reveal the presence of pits containing sensilla on the latero-ventral side of the antenna. All these pits are the opening of deep cavities bearing the same sensilla previously described on Anisoptera antennae. These sensilla are represented by: (i) coeloconic porous sensilla, visible on the antennal surface, whose structure is in agreement with that reported for single walled olfactory receptors, and by (ii) two types of sensilla styloconica (type-1 and type-2), located at the bottom of the cavities and sharing common features typical of thermo-hygroreceptors. The present data allow us to extend previous considerations on the sensory role of the dragonfly antennae to the whole order Odonata, suggesting that olfaction, together with the ability to perceive temperature and humidity, are the main sensory functions of the antennae of these insects.