Sensing taste and odours
Part 5: Distribution and numbers of sensilla
Olfactory sensilla cluster on the antennae, maxillary and labial palps. Sometimes they occur on genitalia as with the sheep blowfly, Lucilia.
Taste sensilla are grouped on and in the mouthparts. Some occur on the antennae since these structures can be used to touch surfaces. They also occur on the legs. Some occur on the wings (e.g of Drosophila). Few occur on the ovipositor, and in some insects, none at all.
Mouthparts of a Heliothis armigera caterpillar showing gustatory sensilla as short spines on the labrum (flap at top). The pair of mandibles below do not have sensilla in the cutting region because they would be damaged by the chewing process. [Image B.W. Cribb] |
Numbers vary between juvenile and adult, and male and female insects. This is probably because of their different needs. Females lay eggs or larvae and must find suitable substrates for their young. A failure to do so would result in a poor survival rate amongst progeny.
Males often need to find females in order to mate and can do so with the aid of chemoreception.
Queen bees and ants have different roles from workers and from reproductive males and therefore have different chemosensory needs. Total numbers of sensilla per flagellum for the carpenter ant, Camponotus japonicus vary from 7500 in workers, 6000 in males, to 9000 in unmated queens. Higher number are associated with the reproductives who must mate, and especially the queen who is responsible for colony control.