Specialist Herbivore Performance on Introduced Plants During Native Host Decline.

Area of Science:

• Ecology
• Entomology
• Conservation Biology

Background:

• Ash (Fraxinus spp.) populations are declining rapidly in the northeastern USA due to the invasive emerald ash borer (Agrilus planipennis).
• This decline poses a threat to insect herbivores specialized on ash foliage, particularly Lepidoptera.
• Nonnative, confamilial shrubs are present in landscapes and may serve as alternative hosts.

Purpose of the Study:

• To evaluate the performance of three ash-specialist hawkmoth species on native white ash and three nonnative alternative host plants.
• To assess the potential of common lilac, weeping forsythia, and European privet as larval host plants for ash-reliant moths.
• To understand the downstream effects of ash decline on specialist insects and inform conservation strategies.

Main Methods:

• Larval performance of three hawkmoth species (Lepidoptera: Sphingidae) was measured on white ash (Fraxinus americana) and three alternative hosts: common lilac (Syringa vulgaris), weeping forsythia (Forsythia suspensa), and European privet (Ligustrum vulgare).
• Key performance metrics included larval survival to pupation, biomass, and growth rate.
• Wing bud malformations at pupation were recorded for caterpillars reared on alternative hosts.

Main Results:

• Nonnative host plants provided varied support for hawkmoth larval survival and development.
• Plant and insect identity significantly affected larval biomass and growth rate.
• Nearly all caterpillars reared on European privet exhibited wing bud malformations, suggesting it may be an ecological trap.

Conclusions:

• Alternative nonnative host plants may be suboptimal for some ash specialists, impacting their survival and fitness.
• European privet poses a significant risk to hawkmoth larvae due to developmental abnormalities.
• Landscaping choices can be strategically made to support threatened insect species during native host decline.