Abstract: In order to illustrate the structure of Haller’s organ and its development in parthenogenetic Haemaphysalis longicornis, the Haller’s organ of ticks from the parthenogenetic population of H. longicornis during different developmental stages (larval, nymphal, and adult stages) was investigated with scanning electron microscopy and the effect of blood feeding on the development of Haller’s organ was also analyzed. The results showed that there was no essential difference in Haller’s organ of all three developmental stages, which is composed of an anterior pit and a capsule. The Haller’s organ contains six sensilla located on the same basal disc in the larva. However, it contains seven sensilla in the nymphal and adult stages. A pored sensillum is located on later-basal disc and other six sensilla are located on the basal disc. The Haller’s organ of the adult was similar to that of the nymph. The area of the Haller’s organ was significantly bigger in engorged individuals than that in unfed ones (P<0.05) during the larval, nymphal and adult stages. The ratio of the anterior pit’s area to the capsule’s has no significant difference between the larval stage and nymphal stage (P>0.05), while has a significant difference between the adult stage and nymphal stage (P<0.05). The development of Haller’s organ occurs in all three stages of the tick and is affected by the blood feeding. The results also indicated that the development of the anterior pit is as fast as the capsule from the larval stage to the nymphal stage, while the development of the anterior pit is faster than the capsule from the nymphal stage to the adult stage. The results partly reveal the development law of the Haller’s organ in H. longicornis.

Key words: Haemaphysalis longicornis, pathenogenetic, Haller’s organ, ultrastructure, development, scanning electron microscope