Common features of the American cockroach

Ryuichi Okada(University of Hyogo)

The American cockroach is a nocturnal, hemimetabolous insect. The American cockroaches are not a social animal such as ants and bees, and  do not have a distinctive nest similar to other insects. They are often observed in places where several individuals aggregate in groups. This has been hypothesized to be due to the aggregation pheromone in their feces. Cockroaches show negative phototaxis and usually move toward dark places rather than places with light, particularly preferring dark narrow places. An experiment showed their highest preference was for dark cracks having a width of 5 mm. They have wings, but are not often observed flying from horizontal surfaces, rather they have often been observed gliding on walls. The motion pattern of legs during walking has often been a subject of studies on coordinated multi-leg motion control. The antennae are often moving during walking(Okada and Toh, 2004).

Olfactory behavior

As can be deduced from their nocturnal lifestyle, the behavior of American cockroaches depends on their olfactory and mechanical senses such as tactile sense rather than on sight. Two olfaction-based behavior are particularly representative as the dependency on smell: mating behavior induced by sex pheromones and the orientation to odor sources by the aggregation pheromone.

The sex pheromone is emitted from the female copulatory organs.  The main component of the sex pheromone of the American cockroach is periplanone B, supplemented with periplanone A. The sex pheromone is detected by the male antenna. Males receiving the pheromone run around looking for the females, extending their wings and abdominal tip. A booming sound can be heard near cockroaches engaging in courtship behavior. In contrast, another type of pheromone that causes other individuals to group together (aggregation pheromone) is contained in the feces, but is actually synthesized and secreted in the gut. Aggregation pheromone seems to adhere to the feces as feces move through the gut. 

Cockroaches have been believed to mostly rely on olfaction for their daily activity. Indeed, it is known that cockroaches have a high sensitivity of olfactory receptors and olfactory learning capability. If cockroaches are presented with an odor that they normally dislike (one that causes aversion) with a reward, they become approaching that odor, i.e., they can memorize the relationship between the odor and the reward. If they are presented with a reward at the same time as being exposed to one odor and a punishment at the same time as another odor, they can distinguish these two odors and gather in favor of the reward smell. This olfactory memory lasts at least 4 weeks (Sakura and Mizunami, 2001). They are also able to distinguish between organic compounds of similar structures that differ by only one carbon chain. (Sakura et al., 2002).

Behavior in response to mechanosensation

The escape behavior of cockroaches based on the mechanical detection of airflow is particularly well known. American cockroaches run in the opposite direction when a frog has just put out its tongue to catch them. Camhi analyzed this behavior in detail and observed that when the frog moves its mouth before protruding its tongue, the resulting slight air movement can be detected by the air sensory hairs on the cercus which is on the tip of the abdomen, and the cockroach runs away in the direction opposite to the source of the air current (Camhi, 1984).


Fig 1 A predating frog with its tongue and the cockroach detecting the frog’s feeding behavior,
quickly changing direction and escaping.(Camhi, Neuroethology, 1984を改変)

Similar to the escape behavior triggered by the air flow stimulus to the cercus, the antennae mediate escape behavior through tactile stimuli (mechanostimuli). The cockroach turns away in the direction opposite to the side the antennae touched. In addition, because of the excellent mechanosensation of responsible sensory hairs on the antennae, the cockroach actively moves the antennae and recognizes different objects through active sensing (Okada, 2002). Through active sensing, the cockroach scans the surface texture of two different objects and can distinguish them(Comer et al., 2003).

Visual behavior

Although cockroaches do not rely on vision, visual senses are indeed functional, and cockroaches are capable of visual learning. When different shapes and patterns were presented with or without punishment, the cockroaches chose the visual cues that were not accompanied by a punishment. Figure 2 shows an experiment on an arena where the floor temperature was high, with only a part of it being at a cool temperature. When the two portions could not be visually distinguished, the cockroach ran around the arena, and when it discovered the cool floor by chance, it settled there (Mizunami et al., 1998). If visual cues in the form of patterns were placed on the arena walls and the cockroach was previously presented with a pattern on the front surface of the cool floor area, the cockroach used visual cues to rapidly move to this area. This experiment shows that cockroaches can not only behave in response to vision but also learn and remember visual cues.


Fig 2 Experimental arena showing that cockroaches are capable of visual behavior and visual learning
(Mizunami, J Comp Neurol, 1998 Modified)


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