Antennal morphology and ultrastructure of Philaenus spumarius (L.)

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera, Cercopoidea, Aphrophoridae), is a polyphagous insect species known to be a vector of Xylella fastidiosa, a quarantine xylematic bacteria associated with the Olive Quick Decline Syndrome in Southern Italy. There is a lack of knowledge in the host location and recognition, as well as in mating behavior of P. spumarius. In this context, the antennae play a crucial role mediating stimuli coming from the environment and from conspecifics. The antennae of both P. spumarius male and female individuals were investigated using Scanning and Transmission Electron Microscopy techniques. The antennae consist of three segments: a basal scape, a pedicel and a flagellum composed of a basal bulb-like enlargement (ampulla) and a long arista. Both the scape and the pedicel are cylindrical with a concave apex. The ampulla surface presents several coeloconic sensilla and three large basiconic structures located close to arista base. Ultrastructural investigation revealed in the arista the presence of a mechanosensory structure probably associated with vibrations perception. Basiconic sensilla show the typical organization of olfactory sensilla as regards the cuticular external structure (which presents abundant wall pores) and the internal cellular features. First insights of TEM investigation of coeloconic sensilla clearly revealed the presence at least two type of sensilla: i) double-walled sensilla, that are the most abundant in the flagellar basal area, possibly involved in chemoperception; ii) aporous thick walled sensilla which show features typical of thermo-hygro receptors. A third third type of coeloconic sensillum is still under investigation.