Prey perceiving predation risk commonly change their behavior to avoid predation. However, antipredator strategies are costly. Therefore, according to the threat-sensitive predator avoidance hypothesis, prey should match the intensity of their antipredator behaviors to the degree of threat, which may depend on the predator species and the spatial context. We assessed threat sensitivity of the two-spotted spider mite, Tetranychus urticae, to the cues of three predatory mites, Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius andersoni, posing different degrees of risk in two spatial contexts. We first conducted a no-choice test measuring oviposition and activity of T. urticae exposed to chemical traces of predators or traces plus predator eggs. Then, we tested the site preference of T. urticae in choice tests, using artificial cages and leaves. In the no-choice test, T. urticae deposited their first egg later in the presence of cues of P. persimilis than of the other two predators and cue absence, indicating interspecific threat-sensitivity. T. urticae laid also fewer eggs in the presence of cues of P. persimilis and A. andersoni than of N. californicus and cue absence. In the artificial cage test, the spider mites preferred the site with predator traces, whereas in the leaf test, they preferentially resided on leaves without traces. We argue that in a nonplant environment, chemical predator traces do not indicate a risk for T. urticae, and instead, these traces function as indirect habitat cues. The spider mites were attracted to these cues because they associated them with the existence of a nearby host plant.

There is a wealth of studies that have examined the way in which prey animals acquire information about their predators, yet the literature on how long prey retain this information is almost non-existent. Here, we investigated if the memory window associated with learned recognition of predators by juvenile rainbow trout was fixed or variable. Specifically, we tested whether the retention of predator recognition was influenced by the risk level associated with the predator. We conditioned juvenile trout to recognize predatory pumpkinseed sunfish posing a high, low or no threat and tested their response to the predator after either 1 or 8 days, and found that trout responded to the odour of the pumpkinseed longer if the risk associated with the predator was higher. We discuss the way in which memory associated with predator risk information provides fundamentally different costs/benefits trade-offs than those associated with foraging.