Invasive predators can alter mimetic interactions between native insects

Invasive non-native predators significantly impact biotic communities, affecting native species through both direct and indirect interactions. Native species have evolved warning colors and defensive mimicry in response to selective pressures from native predators. These adaptations can be influenced by non-native predators, although few studies have focused on their impacts on mimetic interactions. In this study, we examined the impact of the invasive non-native American bullfrog (Aquarana catesbeiana) on the mimetic interaction between two native insect species: the bombardier beetle (Pheropsophus occipitalis jessoensis) and the assassin bug (Sirthenea flavipes). These insects, well-defended against the native pond frog (Pelophylax nigromaculatus), now also confront the invasive bullfrog in Japan. Our laboratory observations revealed that both native and invasive frogs consistently rejected the bombardier beetle due to its chemical defenses. Although 75% of native frogs rejected the assassin bug due to its defensive stab, only 30% of bullfrogs did so. Further experiments showed that bullfrogs’ previous encounters with one of these insects influenced their response to the other. Specifically, bullfrogs with prior exposure to bombardier beetles were less likely to attack assassin bugs. These findings suggest that assassin bugs may benefit more from the mimetic interaction via invasive bullfrogs compared to bombardier beetles, although both insect species benefit from the mimetic interaction via native frogs. Therefore, the presence of invasive bullfrogs could significantly alter the mimetic interactions between these native insect species. Consequently, mimetic interactions between natives may mitigate the impacts of non-native predators on native co-mimics.