What Is a Specialist? Quantifying Host Breadth Enables Impact Prediction for Invasive Herbivores

Area of Science:

• Ecology
• Entomology
• Invasive Species Biology

Background:

• Current classifications of herbivore host specificity (specialists vs. generalists) lack precise definitions, leading to ambiguity.
• Understanding host breadth is crucial for predicting the ecological impact of non-native insects.

Purpose of the Study:

• To quantitatively assess host breadth for 240 non-native, tree-feeding insects in North America using phylogenetic diversity.
• To refine the classification of herbivore host specificity and its implications for invasion ecology.

Main Methods:

• Phylogenetic diversity was employed to quantify host breadth in 240 non-native, tree-feeding insect species.
• Host breadth was analyzed across native and introduced ranges.
• Models were developed to predict ecological impact based on host breadth and insect behavior.

Main Results:

• A refined partitioning of host breadth reclassified 67% of non-native insects from generalists to specialists.
• A reduction in host breadth was observed from the native to the introduced range for these insects.
• An inflection point was identified, correlating host breadth with insect ecological impact and predicting high-impact invaders.

Conclusions:

• Phylogenetic diversity provides a more precise measure of herbivore host breadth, improving classification accuracy.
• Host recognition mechanisms and plant defenses are key factors mediating the impact of novel herbivore-plant interactions during invasions.
• This framework enhances predictions of non-native forest insect impacts.