Everett Booth

Date of Award

5-2015

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Entomology

Advisor

Andrei Alyokhin

Second Committee Member

Seanna Annis

Third Committee Member

Frank Drummond

Abstract

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is considered to be one of the most destructive insect defoliators of potato wherever present. Due to its voracious feeding habits across multiple life stages, beetles are capable of causing complete defoliation, which can lead to severe yield reductions and even complete crop loss. Currently, work pertaining to this species has investigated natural feeding habits on common host plants, but few studies have looked at less common foraging options such as consumption of virus-infected host plants and conspecifics.

Agricultural systems are often simultaneously impacted by multiple stressors. However, most studies explore these threats at the individual level. In our study, we investigated the effects of two commonly occurring viruses of potato, Potato virus Y (PVY) and Potato leafroll virus (PLRV) on host plant selection and utilization across various spatial scales by the Colorado potato beetle. Adult beetles selected PLRV- infected foliage in the cage choice trails, and larvae that fed exclusively on PLRV- infected foliage developed into larger adults. PVY-infected foliage was avoided in the cage trials and had no effect on the weight of developing adults. In field trials, preference and utilization of potato plants was more dependent on plant size than on virus infection. These results demonstrate that while virus-infected plants can cause physiological changes that influence beetle preference, beetle abundance and/or distribution is driven by different factors at the field level. Additionally, this study demonstrates the importance of investigating the applicability of laboratory findings at the field level before making any far-reaching conclusions.

Colorado potato beetles are traditionally considered polyphagous herbivores. However, previous work suggests that this species commonly partakes in cannibalism, with conspecific larvae being the most common predators of eggs. In our study, we manipulated laboratory conditions in an attempt to observe and quantify cannibalism at the adult stage. To the best of our knowledge, our study is the first recorded case of adult cannibalism within this species. In addition, we investigated factors that might influence cannibalism rates and were able to conclude that size, maturity, wounding, and crowding all had significant effects on the frequency of this behavior. As expected, factors that increased the vulnerability of the individual also influenced its chances of becoming consumed. More work would be needed to investigate the nutritional benefits of this behavior, as well as its occurrences in natural populations, but doing so could shed light on its potential evolutionary role in this insect.

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