Date of Award:

8-2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

Diane G. Alston

Committee

Corey V. Ransom

Abstract

By outcompeting desirable vegetation, invasive weeds can dominate field crops and rangelands, drastically reducing yield and land value. One option in controlling the impact and spread of such weeds is reuniting them with their natural insect herbivores, a process called biological control. When successful, biocontrol can be the cheapest way to provide long-term control of invasive weeds, but continual monitoring of insect and weed activity is required to ensure success.

Dalmatian toadflax is an invasive weed that occurs widely throughout the northwestern U.S., and that is spreading south each year to warmer and drier regions, including sites in Utah. Although successful in the northwest, biocontrol of Dalmatian toadflax using a stem-mining weevil, Mecinus janthiniformis Toševski and Caldara (Coleoptera: Curculionidae), has been slow to occur at sites in Utah and elsewhere in the weevil’s current southern range. By making field assessments of insect activity at sites in Utah, this study aimed to evaluate the limitations of weed control in these southern regions including inadequate timing of biological events (phenology) and the mortality of adult weevils during the winter and of individuals during summer development to adulthood.

This study found that weevils at sites in Utah were synchronized well with the biology of Dalmatian toadflax, but the sexes differed in their phenology in that males emerged from overwintering sites considerably earlier than females (a phenomenon called protandry). Overall survival of weevil adults during winter, and larvae during summer development to adulthood was high, (83% and 65%, respectively). The majority of M. janthiniformis deaths (51%) in live stems during the summer were the result of attack by parasitoid wasps. These wasps, and adult weevils, were found in association with exit holes observed in live Dalmatian toadflax stems during the summer. Overall survival of weevils from larval development in the summer, to adult emergence from overwintered stems in the following spring, was >50%.

Although suppression of Dalmatian toadflax was slow to occur at Utah sites, this study indicates that the phenology and low mortality of M. janthiniformis in Utah should contribute to effective biocontrol. Although other factors that may limit weed control were not considered in this study, M. janthiniformis appears to be capable of surviving and controlling Dalmatian toadflax in southern regions of North America. Phenology models and estimates of mortality of M. janthiniformis generated in this study can contribute to the implementation of future biocontrol control programs for Dalmatian toadflax.

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