Antennal morphology and sensillum distribution of female cotton leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae)

Female cotton leaf worm Spodoptera littoralis (Biosduval) is highly dependent on its antennal sensory structures for host location for feeding or oviposition. The external structure, number, and distribution of the antennal sensilla of female S. littoralis were examined with light and scanning electron microscopy. The antenna of adult female is filiform, composed of a scape, a pedicel and a flagellum. The flagellum has 65–80 segments densely packed with sensilla distributed on the ventral surface and lateral edges of the flagellum except the dorsal surface which is packed with scales. Eight types of sensilla; trichodea, basiconica, auricillica, coeloconica, uniporous peg, chaetica, styloconica, and squamiformia were detected. Total number of antennal sensilla varied among different antennal portions. Proximal segments showed significantly more short trichoid and basiconic sensilla than distal ones, while distal segments have the longest sensilla chaetica. Last antennal segment carries the higher number of sensilla chaetica than other segments and ends with an apical crown which has 1–3 branches, each is endowed with 4–6 apical aporous sensilla styloconica. The possible function of the antennal sensilla is discussed in relation to their morphology.