Date of Award

2021

Document Type

Honors Thesis (Colby Access Only)

Department

Colby College. Biology Dept.

Advisor(s)

Judy L. Stone

Second Advisor

Catherine R. Bevier

Third Advisor

Caitlin McDonough MacKenzie

Abstract

Ash (Fraxinus spp.), an important tree genus across the northeastern USA, is imperiled as a result of an invasive forest pest, emerald ash borer (Agrilus planipennis). With the absence of ash an imminent threat, we sought to quantify the effects on several species of insect reliant on ash as a host-plant. In so doing, we identified three other plant species phylogenetically related to ash which may serve as potential alternative host-plants. Each of these is a non- native, cultivated shrub species common in managed landscapes in New England. Next, we measured larval performance (growth rate and biomass) on each of the potential alternative host-plants in addition to white ash (Fraxinus americana). Our results show that the non-native host-plants do support larvae to pupation, albeit with smaller growth rates and less biomass attained at certain developmental benchmarks. Caterpillars reared on one alternative host- plant—European privet (Ligustrum vulgare)—exhibited gross malformations of the wing buds. This result suggests that privet may constitute an ecological trap, whereby female moths preferentially lay on a sub-optimal host-plant resulting in reduced fitness of the offspring. Therefore, our findings show that performance testing is important to teasing out the species- specific effects of alternative host-plants on insect fauna. We found that not all cultivated host- plants are uniformly able to support specialist insect populations, suggesting that landscaping decisions can play an important role in perpetuating threatened species.

Keywords

ecological trap, specialist, Lepidoptera, invasive species

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