|
| Category | Function | General characteristic sensilla of insects | Types of labial sensilla distinguished in the Nepomorpha (see results) |
|
(A) Mechanosensilla
Sensillum has 1 neuron.
Dendrite is not branched and is attached by the cuticular sheath either to the center or to one side of the base of the hair. The cuticular sheath may continue beyond the end of the dendrite and insert into wall of the hair at various distances beyond the base
[4, 8]. | Tactile
[6, 8, 24]. | Mechanosensilla vary greatly in size and form and are shaped as thin hairs, chaetica, trichodea, trichobothria scale, filament, and peg. The shafts of sensilla protrude from the surface of cuticle, and their base is attached by an articulation membrane forming the flexible socket. The hair is usually drawn to a sharp tip and exteriorly may bear cuticular sculpturings such as grooves or spicules. Mechanosensilla have a wall-nonpore except the molting pore near the base [6, 8].
NP: nonpore. | Various shaped sensilla sunken into
a flexible socket:
chaetica sensilla (CH): (CH1 long, CH2 middle, and CH3 short), conical (COS)—prioprereceptor, basiconic (BAS), squamiforme sensillum (SQS), trichobothrium (TBS), clubbed-like (CBS), paddle-like (PDS), cupola-like (CUS), peg (PES), finger-like (FRS), freniale-like (HLS), chaetic sensillum with bisected tip (CHB), stars-like (STS), multilobes (MPS), ribbon-like (RBS), long (RBS1), and short (RBS2). |
|
(B) Contact-chemoreceptive sensilla (bimodal sensilla)
Sensillum has 3–10 neurons [28].
Chemosensitive dendrites are not branched and extend to tip of cone within dendrite sheath, which also ends in tip of cone. In addition, sensillum has a mechanosensitive neuron ending at the cuticle of the cone base and a tubular body [4]. | Gustatory and tactile
[6, 28]. | The contact-chemoreceptors are short as well as hairs or various cones characterized by presence of a single pore at or close to the tip of the projection. These sensilla are placed on the surface and equipped with an articulation in a socket. They are often wider at base and gradually tapering towards the apex. The cuticular walls of these sensilla are smooth, with the molting pore near the base [4, 6].
Tp: with one terminal pore: uniporous. | Sensilla sunken in a flexible socket:
trichoid sensilla (TRS): (long TRS1, short TRS2). |
|
(C) Chemoreceptive sensilla
(unimodal sensilla)
Sensillum has 3–10 neurons [28]. Chemosensitive dendrites are the same as in contact-chemoreceptive sensilla but do not possess the mechnosensitive neuron [4]. | Gustatory
[6, 7, 15, 28]. | The gustatory receptor can be located in a hair, papilla, basiconic, peg-, or plate-like elevations of the surface or beneath the flat areas that have a single terminal pore (TP-sensilla, uniporous).
Generally, their base is sunken into inflexible sockets. The presence of the pore at the end of the sensillum shows their chemical function [6, 7].
Tp: with one apical pore: uniporous. | Sensilla sunken in an inflexible socket: papilla (PAS): (PAS1 with flattened tip, PAS2). |
|
(D) Chemoreceptive sensilla
Sensillum has 3 neurons. The dendrites of the two neurons extending into lumen of peg are hygrosensitive. A third dendrite ending below the base of the peg is thermosensitive. All dendrites are surrounded by dendrite sheath [4]. | Hygrosensitive and thermosensitive [6]. | Coeloconic sensilla are usually concealed in a pit of cuticle and it is without pores [6].
NP: nonpore. | Peg-in-pit sensilla (PIP):
with an inflexible socket sunken in cavity. |
|
