Photoperiod-dependent release of suppression pheromone in the male lobster cockroach Nauphoeta cinerea.

The complex agonistic repertoire between male lobster cockroaches (Nauphoeta cinerea) makes this species an excellent model for aggression studies. During the establishment of dominance hierarchies, 3-hydroxy-2-butanone (3H-2B) functions as a suppression pheromone, keeping the rivals in a submissive state. In the present study, we evaluated the release of 3H-2B by dominant individuals across four different time phases within the 24-h photoperiod, i.e., early scotophase (ES), late scotophase (LS), early photophase (EP), and late photophase (LP). For each time phase, we collected volatile pheromones during a 60-min first-encounter fight to measure the level of released 3H-2B. Subsequently, the amount of 3H-2B remaining in the sternal glands of dominant and subordinate individuals was measured and compared to socially naïve male controls. Release of 3H-2B was relatively high during ES or LP first-encounter fights, compared to LS or EP encounters. The attack duration and aggressive posture intensity in dominant males were positively correlated with the amount of 3H-2B release in all four phases. A similar statistical distribution was found between the amount of 3H-2B released by dominant males and the amount of 3H-2B in the sternal glands of naïve male sternal during LS, EP, and LP. However, during ES, the statistical distribution of 3H-2B released by the dominant was significantly greater than the distribution of 3H-2B content in socially naïve male sternal glands. The observed phase-dependence of 3H-2B release might be due to variations in 3H-2B biosynthesis or the scotophase-specific behavior of naïve males, wherein an aggressive posture is spontaneously adopted with concomitant 3H-2B release.