Jie Chen

Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Entomology

Advisor

Andrei Alyokhin

Second Committee Member

Eleanor Groden

Third Committee Member

Frank Drummond

Abstract

The Colorado potato beetle (Leptinotarsa decemlineata) is known as the most noxious pest of plants in Solanaceae family. Since the first major outbreak, the Colorado potato beetle has been detected in North America, Europe, and Central Asia. Although chemical control still remains the choice for the management. Colorado potato beetle has capability of developing insecticide resistance to nearly all the chemicals used against.

Biological variation commonly exists in insects because of genetic or non-genetic inherited variations, as well as due to different individual experiences of an ambient environment. As the geographic range increases, the variation becomes key to the survival of the organism in the new habitat. In this study, we investigated insecticide resistance and growth potential in beetle populations collected from different locations in the United States. The differences were detected in insecticide resistance, egg mass size, and egg hatchability. Large egg mass size appeared to be offset by lower egg hatchability. The intrinsic population growth rates were different among the strains, but not correlated to the insecticide resistance. Interestingly, we detected a female-biased sex ratio at least in one of the strains. Lack of fitness costs may be partially responsible for the Colorado potato beetle’s high propensity to develop insecticide resistance, although reduced relative fitness has been also demonstrated for a number of insecticide-resistant strains. Our results also highlight the difficulty of investigating pleiotropic effects of genes conferring insecticide resistance because genetic differences between the strains are not necessarily limited to such alleles.

Temperature, which is a major abiotic factor for ectotherms, plays a vital part in physiology and biochemistry of insects. Heat shock protein is a highly conservative subset of molecular chaperones that is in charge of transport, folding, unfolding, assembly, and disassembly of multi-structured protein units and degradation of misfolded or aggregated proteins. Previous studies have also indicated that temperature stress may be more detrimental for insects treated with insecticides. In our study, thermotolerance at 43 °C was similar for different geographical strains. Imidacloprid applications reduced expression of the Hsp70 heat shock protein at both optimal and extreme temperatures. As a result, exposure to the heat shock was more detrimental to the survivorship of the imidacloprid-treated larvae. Although the laboratory study had different conditions compared to the potato field, our results suggest that insecticide applications in the field could be more effective during the warmer parts of the season and at higher temperatures during a day. Future field studies would provide more practical guidance to take full advantage of the reported interactions.

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