Olfaction foraging in visually oriented tropical arboreal ants Oecophylla smaragdina: Implications for insect predation studies using artificial sentinel prey

Predation is the key to understanding trophic interactions. Because of the brief and cryptic nature of predatory behavior, sentinel prey has been widely adopted as an indirect way to identify predators and understand trophic interactions. However, sentinel prey presents only static visual cues, potentially biasing toward visually oriented predators whilst ignoring those that require other sensory cues to forage. Despite this, the effectiveness of sentinel prey has rarely been tested. Here, we focused on the weaver ant, Oecophylla smaragdina, a keystone predator widespread in the Asian and Australian tropics. As this species has large eyes and is known to visually navigate in their arboreal habitats, we hypothesized that they rely on visual cues to forage and that their predatory behavior will be captured by caterpillar-shaped sentinel prey. Ants were collected as colonies, and preference trials on baits were conducted using combinations of olfactory and static visual cues including the caterpillar shape. Surprisingly, O. smaragdina showed little or no preference for baits in the absence of olfactory cues and did not differentiate the shapes of baits regardless of the presence of olfactory cues. Our results indicate that O. smaragdina is likely to make predatory decisions based primarily on olfactory cues, while visual cues might be used for other behaviors. Furthermore, O. smaragdina is likely to be left out by the predation studies using sentinel prey models which is particularly alarming considering the dominant role of this species in the trophic interactions of tropical rainforests. Our study demonstrates that morphological characteristics, arboreal habitats, and visually oriented behavior do not necessarily suggest the use of static visual cues for predatory decisions. We suggest that sentinel prey models should not be used alone when the dominant predators are unlikely to use visual cues to make predatory decisions.