Displays of intraspecific and interspecific overt agonistic behavior between colonies of Reticulitermes flavipes (Kollar) and colonies of Reticulitermes virginicus (Banks) were observed in laboratory assays. All possible combinations of arena sizes (1.3, 3.5, 6.0, and 9.0-cm) and group sizes (1, 2, 5 and 10 workers per arena) were assessed for effects on interspecific and intraspecific agonism. Agonistic behavior was scored positive in arenas if half or less of the starting number of termites was alive after 24 h. Thirty-six percent of arenas with interspecific pairings were agonistic in all combinations tested while 4.5% of arenas with intraspecific combinations showed aggression (N = 544 and N = 288, respectively). Two interspecific pairings provided scores that were not statistically different from intraspecific combinations. These assays indicate that evidence of overt agonism between worker termites from these two Rhinotermitid species is not a reliable indicator to differentiate species. Encounters in the two larger arena sizes resulted in significantly more agonism than the two smaller arena sizes. Group size had little apparent effect on the frequency of positive agonistic interactions. Possible reasons for the variable overt agonism scores are discussed.

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