IP Nervous

Cold receptors on the body surface of the Tropical Bont tick Amblyomma variegatum

A. Widmer, M. Vlimant, P.M. Guerin & P.A. Diehl

Institute of Zoology, University of Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland

Ticks make use of thermal cues in addition to other sensory modalities for survival. Amblyomma variegatum possesses warm and cold receptors in each of two long poreless sensilla at the tip of each of the foreleg tarsi. These appendages are employed by ticks while searching for a host. Now we have discovered cold receptors scattered over the body surface of A. variegatum. Ultrastructure investigations reveal that all of these sensilla have a terminal-pore structure and contain a tubular body in addition to five receptor cells. The cell we suspect to be the cold receptor is much bigger than the others and possesses two ciliary bodies giving rise to two outer dendritic segments. These dendritic segments are invaginated proximally and then branch extensively within two sets of sensilla. The first set is comprised of 20 sensilla that are 10µ long and concentrated bilaterally on a non-sclerotized section of cuticle on either side of the basis capitulum. The second set of 8-10 slightly longer sensilla occurs around each eye. The other 100-120 terminal-pore sensilla containing cold receptors are much longer than the others and are scattered over the rest of the body. The latter sensilla are characterised by the fact that the outer dendritic segments of the big receptor cell are neither invaginated nor branched. Electrophysiological responses from these cold receptors were recorded using an airflow switching device that delivered different T° shifts to the preparation. The responses of these receptors show the highest gain to small drops of temperature, still clearly responding to a ?T° of 0.02°C. Evidence from behavioural tests will be provided to show how these receptors contribute to survival of A. variegatum.

Index terms: Amblyomma, thermoreception, cold receptor, behaviour, sensory physiology.

Copyright: The copyrights of this original work belong to the author (see right-most box in title table). This document appears in Session 1 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.