New FISC Study Challenges the Biotic Resistance Hypothesis in Forest Insect Invasions

In their article, the authors focus on bark and ambrosia beetles (Scolytinae and Platypodinae) – a group that includes many economically and ecologically important invasive forest pests. Using a unique, large-scale dataset covering the entire conterminous United States, the team analysed patterns of both native and non-native beetle species richness in relation to tree diversity, native insect diversity, climate and socio-economic factors.

The results provide little support for biotic resistance in this insect system. Instead, higher native tree diversity had little or no effect on invasions by non-native bark and ambrosia beetles. Furthermore,  native beetle diversity was generally positively associated with non-native species richness, opposite of what would be expected under the biotic resistance hypothesis. Instead, the strongest predictor of invasion success was the availability of non-native host trees, along with indicators of human activity linked to propagule pressure.

These findings point to fundamental differences between plant and insect invasions. Whereas interspecific competition often constrains plant invasions, it appears to play a much smaller role in shaping invasion patterns of forest insects.

The study contributes to a growing body of evidence suggesting that biodiversity alone cannot be relied upon as a defence against insect invasions and highlights the importance of host availability and human-mediated pathways in shaping future invasion risks.