In three experiments with free-flying honeybees, the previously discovered overlearning-extinction effect was replicated under different conditions and shown to depend on magnitude of reinforcement: The effect appeared in training with a 50% sucrose solution but not with a 20% solution. The results prompted a fourth experiment in which successive negative contrast was demonstrated: The animals were disturbed to find the 20% solution on a distinctive target that always before had been baited with the 50% solution. The conclusion is that the overlearning-extinction effect is an instance of contrast and can be understood in terms of frustration engendered by unrealized anticipation of reinforcement.