Abstract

Unlike vertebrates the taste receptors of insects are distributed
over the mouthparts, body and legs. In insects
the sense of taste is used to select and reject food, select
appropriate egg-laying sites and to avoid noxious chemicals
in the environment. Here we have analysed some
of the coding properties of the taste receptors, or basiconic
sensilla, on different regions of the legs of locusts
and related them to behavioural responses evoked
through chemical contact.
We analysed the responses of taste receptors to two
behaviourally relevant chemicals, sucrose and sodium
chloride (NaCl). In response to stimulation with 500
mM NaCl sensory neurones innervating receptors along
the dorsal or ventral surfaces of the hind and fore legs
progressively produced more spikes towards the tarsus,
so that tarsal taste receptors responded at twice the frequency
(approx. 20 Hz) of proximal sensilla (approx.
10 Hz). Similarly, 100 mM sucrose applied to distal
receptors on the hind and fore legs evoked more spikes
than when applied to proximal receptors. Basiconic sensilla
tested with a range of NaCl concentrations were
more sensitive on the tarsus compared to proximal sites.
Behavioural studies showed that the frequency of leg
withdrawal movements to droplets of chemicals applied
to a leg increased with increasing NaCl and sucrose concentrations.
For a given concentration the frequency of
withdrawal was greater when it was applied to the tarsus
compared to proximal femur. The foreleg was more
responsive than the hind leg to NaCl whereas the frequency
of withdrawal was similar for sucrose for both
legs.