Host Range Expansion and Dual Ecological Roles of an Invasive African Seed Predator on Native and Introduced Plants...

Invasive seed predators can severely affect the reproduction of long-lived trees, especially when host range expansion occurs. The beetle Specularius impressithorax (Chrysomelidae: Bruchinae), native to Africa, has become established in Hawai'i where it attacks the endemic coral tree (Erythrina sandwicensis; Wiliwili). Here, we report the infestation of an African coral tree (E. livingstoniana) by this beetle and assess its performance and oviposition patterns on native and non-native hosts. Field surveys showed that eggs were aggregated on both hosts but more abundant on E. sandwicensis than on E. livingstoniana. Laboratory assays revealed no difference in larva-to-adult survival between the two hosts, although adults emerging from E. sandwicensis were larger. Choice tests indicated no oviposition preference between the two Erythrina species, despite the larger seed size of E. sandwicensis. To explore potential host range expansion, trials were run on economic legumes with varying phylogenetic distance from Erythrina, which showed oviposition on peanut (Arachis hypogaea) with low but successful survival (10.3%), while no development occurred on broad bean or pigeon pea. More E. sandwicensis seeds germinated when infested by a single early-stage larva (70% germination) than when uninfested (20%), suggesting that minimal seed predation may facilitate germination because previously reported greater damage induced by infestation through adulthood reduces germination. Our findings highlight the ecological flexibility of an invasive bruchine, its potential to exploit other Faboideae plants, and the dual role of seed predators as both threats and facilitators of seed germination. These results have implications for conservation of endemic coral trees and for understanding invasion dynamics of shared seed predators. Additionally, we examined non-botanical substrate filled with seed powder for oviposition and compiled global host records of S. impressithorax to contextualize its host range expansion.