The response of isolated, adult male H. bimaculatus to stationary dummies varies between individuals and, to a lesser extent, within individuals over a time period of several days or weeks. This is due, presumably, to differences in the relative activation of motivational systems that occur between individuals and to shifts in such activation within an individual, respectively. Certain activities ... [Show full abstract] that occur during dummy presentation - biting, quivering, fluttering and finrest - and which are considered to be associated with separate motivational systems of attack, sexual and escape behavior (ROWLAND, 1975) were utilized to study system interaction. An attempt was made to manipulate the different systems by presenting subjects with dummies of varying size and color. All of the activities listed above could be elicited, although in some cases only rarely, by each of the different size and color dummies. However, a dummy's effectiveness in eliciting a particular response depended both on its size and color. Males that attacked both red and green dummies often showed a higher bite frequency to the former. Biting in such males also tended to increase with increasing dummy size, but in most males a limit was reached, after which further increase in dummy size led to a decrease in biting. Indications that fluttering and/or finrest were increasing when biting decreased suggests that this drop resulted from interference of expression of the attack system caused by activation of escape. In several cases males attacked a green dummy but appeared to be inhibited from attacking the same size red dummy. It is suggested that this is because the red dummy strongly stimulates sexual behavior, which in turn, interferes with activities, such as biting, associated with the attack system. Moreover, males that had previously courted red dummies could be induced to attack them by allowing these males to pair and spawn with a live female (this effect was observed even several days after the female was removed) suggesting that deactivatian of the sexual system and/or activation of parental behavior will facilitate the expression of attack. Courting males showed much higher levels of quivering to red dummies than to green ones; quivering to green dummies was only occasionally observed. Quivering to red dummies also tended to increase with increasing dummy size, a result which could be due to increased conflict between attack and escape systems, increased activation of the sexual system, or both. There was some indication that fluttering was higher to red dummies, but this was not statistically significant. Fluttering and/or finrest tended to be higher in the presence of larger dummies than in the presence of smaller ones, at least in attacking males that showed some tendency to perform these activities. It appears that increasing size of a dummy tends to increase its effectiveness in activating behavior via a less specific arousal mechanism while the increased effectiveness of red coloration is due to a more specific mechanism. The results are viewed in terms of interaction among systems of attack, escape and sexual behavior and the role of such interaction in the causation and ritualization of courtship behavior is briefly discussed.