How specialists and generalists herbivores are responding to invasive plant threats

Background/Question/Methods

Understanding the impact of invasive species on native ecosystems is important both ecologically and economically. The purpose of this study was to investigate potential outcomes of novel interactions of native insect herbivores with invasive plants. We investigated interactions of the specialist honeysuckle sawfly (Zaraea inflata) with native (Lonicera reticulata and Symphoricarpos albus) and invasive (Lonicera maackii and Lonicera japonica) honeysuckle species. We also examined the interactions of the generalist fall webworm (Hyphantria cunea) with native (L. reticulata, Viburnum. prunifolium, Ulmus americana, and Prunus serotina) and invasive (L. maackii, L. japonica, Lonicera tatarica, Pyrus calleryana, and Elaeagnus umbellata) plant species. Adult Z. inflata sawflies and H. cunea moths were captured and reared in a laboratory to observe oviposition rates and preferences on native and invasive species. Next, no-choice bioassays were conducted with Z. inflata larvae and H. cunea caterpillars to determine how well they utilize various native and invasive plant species. Lastly, choice bioassays were conducted to determine host preference of Z. inflata larvae and H. cuneacaterpillars.

Results/Conclusions

The honeysuckle sawfly adults strongly preferred to oviposit on native honeysuckle species compared to invasive honeysuckle. However, larvae of this insect had similar survival and performance on L. reticulata, S. albus, and L. maackii. The larvae performed the worst on L. japonica. When the larvae were given a choice between native and invasive plant leaves, the larvae strongly preferred the native species. Fall webworm adults oviposited equally on native and invasive plants.  Larvae of this insect displayed some variation in performance on native and invasive honeysuckle species. When given a choice between native and invasive plants, however, they preferred native plants. Overall, both the honeysuckle sawfly and the fall webworm generally prefer familiar native plants over novel invasive plants even, in some instances, when they can perform equally well on the invasive plants. Understanding factors that influence host choices of adults and larvae could benefit efforts at using native insects as biocontrol agents.