http://link.springer.com/article/10.1007/s00359-004-0582-8#page-2

Abstract

Chemical stimulation of contact chemoreceptors located on the legs of locusts evokes withdrawal movements of the leg. The likelihood of withdrawal depends on the site of stimulation, in addition to the identity and concentration of the chemical stimulus. A significantly higher percentage of locusts exhibit leg avoidance movements in response to stimulation of
distal parts of the leg with any given chemical stimulus
compared to proximal sites. Moreover, the percentage of
locusts exhibiting avoidance movements is correlated
with the density and sensitivity of chemoreceptors on
different sites of an individual leg. The effectiveness of
chemical stimulation also differs between the fore and
hind legs, with NaCl evoking a higher probability of leg
withdrawal movements on the foreleg. Moreover, sucrose
was less effective than NaCl at evoking withdrawal
movements of the foreleg, particularly at low concentrations.
The gradients in behavioural responses can be
partially attributed to differences in the responsiveness and density of the contact chemoreceptors. These results may reflect the different specialization of individual legs, with the forelegs particularly involved in food selection.

Keywords Sensory neuron, Contact chemoreception,
Gustation , Insect ,Grasshopper