An Aggregation Pheromone of the German Cockroach Blattella germanica L. (Orthoptera : Blattellidae) : I. Site of the Pheromone Production

Gregariousness has been found in the german cockroach, Blattella germanica L. Young nymphs of the german cockroach aggregate when they are resting. When newly hatched nymphs reared in solitary, the growth and development were delayed. The gregariousness is considered to be favourable for the existence of this insect. The facts that the aggregation was observed even in darkness and that the antennae played an important role for the aggregation suggest that chemical stimuli would be responsible. Active principle responsible for the aggregation was found both in the faeces and in ether washing of the body surface. Ether washing of the posterior portion of the abdomen showed higher activity than the other portions. These results indicate that the active principle would be produced either externaly or internaly in the region of the anus. As the result of histological studies, it was found that the epithelium of the rectum forms six rectal pads consisting of single layer of cells showing glandular nature. Filter papers conditioned with the german cokroaches whose abdominal tips had been amputated did not elicit the response for the aggregation, while those impregnated with methanol extract of the rectums dissected did. It is concluded that the active principle seems to be secreted from the rectal pad cells into the lumen of the rectum when faecal materials are passing, and then excreted with the faeces. The active principle found in the body surface was considered to be of the same origin as found in the faeces, and it adsorbed onto the body surface by its lipid nature. This active principle playing as an attractant for the aggregation seems to be a new kind of pheromone. We offer the term "aggregation pheromone" to this pheromone.