THE SENSORY NERVOUS SYSTEM OF THE ADULT CATTLE TICK <i>BOOPHILUS MICROPLUS</i> (CANESTRINI) IXODIDAE. PART III. ULTRA‐STRUCTURE AND ELECTROPHYSIOLOGY OF CHELICERAL RECEPTORS

Abstract

Abstract The inner and the outer cheliceral digits of the cattle tick B. microplus have been investigated with transmission electron microscopy and found to be innervated by sensory neurones. The outer digit has a terminal papilla innervated by two neurones which appear to be mechanoreceptors and two sensory pits, one pit innervated by eleven neurones some of which are chemoreceptors, and the other pit by a single neurone containing an unusual vacuolar organelle. A pair of neurones, which appear to be mechano‐receptors, innervate the shaft of the inner digit where it joins the cheliceral hood membranes. Thus a total of 16 neurones are located in each inner digit of the chelicerae of B. microplus. Each outer digit has a complement of 13 neurones of unknown function. Characteristic chemoreceptor responses to solutions of sodium chloride, adenosine triphosphate, reduced glutathione and bovine plasma have been recorded from the pit sensilla of the inner digit by electrophysiological techniques. This work adds a sensory function to the chelicerae of ticks, appendages that are generally regarded as mere cutting tools. The identification of chemosensory sensilla responding to blood chemicals within the feeding lesion may have implications for work on tick‐host specificity and the phenomenon of host resistance to ticks.