CHC sensillum

Figure 10.1 Aggressive behavior of Camponotus japonicus and the CHC sensillum on the antennal surface. Left Photograph of Camponotus japonicus encountering a non-nestmate worker ant. Right Scanning electron micrograph (SEM) of the antennal surface. The non-nestmate-CHC-sensitive sensillum is indicated by an arrow.

Figure 10.2 Schematic drawing of the perireceptor model in an ant CHC sensillum catching CHC molecules.

Figure 10.3 Electrophysiological response of the CHC sensillum to nestmate or non-nestmate CHCs with or without CjapCSP. Left column Recordings to stimulus solutions of 10 mM NaCI, 10 mM NaCI plus CSP and 10 mM NaCI plus bovine serum albumin (BSA). Middle column Recordings to non-nestmate CHCs dissolved in the same stimulus solutions. Right column Recordings to nestmate CHCs dissolved in the same stimulus solutions.

Another unsolved problem is the mechanism of a sort of filter function of the CHC sensillum, which cuts off the chemical information of nestmates and passes that of the non-nestmates. Moreover, the CHC sensillum of Camponotus japonicus, housing about 130 receptor neurons, could potentially distinguish 2130 different patterns by an on/off combination of 130 receptor neurons. This number of receptor neurons in a sensillum seems too large to recognize CHC blends of 18 components, although the sensillum might need to respond to CHCs not only of its own species, but also of other species. 

Much is still unknown about the use of the CHC sensillum. Using natural and synthetic hydrocarbons, more precise studies should be done at both neuronal and behavioral levels. 

Generally, the taste sensillum contains only small numbers of receptor neurons for fundamental tastes. Hence, the taste sensillum might not be suitable for perception of CHC pheromones that contain many components. For such multi-component pheromone perception, olfactory sensilla with many receptor neurons might be more suitable, even though CHC contact pheromones are non-volatile in most cases. 

In addition to the Drosophila sex pheromone CHCs mentioned above, it is well known that CHCs are used by ants for various chemical communications nestmate recognition, caste discrimination, etc. (see related chapters). In various ant species, chemical analysis of the body surface materials suggested that the colony-specific blends of a multi-component CHC mixture act as the nestmate-discriminative pheromone (Bonavita-Cougourdan et al., 1987 Yamaoka, 1990 Howard, 1993 Vander Meer and Morel, 1998 Howard and Blomquist, 2005). In a Japanese carpenter ant, Camponotus japonicus, the CHC pheromone, consisting of 18 CHC components of 20-40 carbons, is used as a chemical cue for nestmate and non-nestmate discrimination (Yamaoka, 1990). Because of the antennation behavior for inspecting encountered ants, the CHC-sensitive sensillum was expected to be discovered on the antenna. 

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