Differential Effectiveness of Anti-Predator Defenses in Non-Native Leaf Beetles Against Native Frogs and Lizards

Predators constitute an important source of biotic resistance influencing the establishment and population increase of non-native species, and the strength of this resistance depends on how effectively predators tolerate or overcome the defenses of non-native prey. In this study, we compared the effectiveness of defenses in the non-native leaf beetle Lema diversipes and its closely related native congener L. decempunctata (Coleoptera: Chrysomelidae) against two native predators: the Japanese tree frog, Dryophytes japonicus (Anura: Hylidae), and the Japanese skink, Plestiodon japonicus (Squamata: Scincidae). Adults of both beetle species secreted chemicals from their elytra when stimulated. To investigate defensive effectiveness, individual adults were provided to predators under laboratory conditions. All adults of both beetle species were attacked and consumed by tree frogs, whereas 93% of L. diversipes and 60% of L. decempunctata were rejected by skinks. These results indicate that the beetles' chemical defenses are more effective against skinks than against tree frogs. Consequently, native tree frogs may exert stronger biotic resistance than native skinks, and tree frogs potentially suppress the population increase of L. diversipes. Overall, our findings show that chemical defense effectiveness varies between predator groups, highlighting the importance of predator diversity in shaping invasion outcomes.