Date of Award:

5-2020

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee

Edward Hammill

Committee

Trisha Atwood

Committee

Ricardo Ramirez

Abstract

The global human population is expected to reach 9.8 billion by 2050 and an increase in food yield will be needed to provide for the future generations. Insects are among the biggest threats to food production and are therefore the subject of intense chemical control through the application of pesticides. The ability of insects to evolve resistance to pesticides after repeated use has been documented. However, how evolved responses affect individuals’ behaviors, their interactions with others, and how these factors impact overall patterns in distribution remains relatively unexplored in the bromeliad.

The aquatic insect communities housed in water-holding tropical plants (i.e. bromeliads) were collected from areas with a history of repeated pesticide application (“plantation”), and protected areas without such exposure (“pristine”).The insect communities living in the bromeliads were compared between the plantation and pristine sites.The most common damselfly predator and mosquito prey were collected and then subjected to increasing concentrations of the pesticide Dimethoate in order to determine the species’ susceptibility (i.e. the concentration that kills them). Susceptibility between mosquitoes from pristine and plantation (where pesticides were used) populations were compared, and an increased tolerance of populations was considered to be evidence of an adaptive response. This thesis then explores deeper, investigating how evolved resistance may influence how an organism behaves, and whether resistance changes how they interact with other species.

At the community level, bromeliads from areas with a history of pesticide application were found to hold more simple communities with fewer predators, than bromeliads from the pristine sites. When susceptibility was compared between populations from pristine and plantation locations, mosquitoes appear to show selective resistance to pesticides, but their damselfly predators do not. Sub-lethal pesticide exposure was found to alter the mosquitoes’ behavior differently depending on where the mosquito was collected. The number of mosquitoes consumed by the damselfly predator when exposed to pesticides also differed depending on where the mosquitoes were collected. Mosquitoes from plantation bromeliads moved less in pesticides and were also consumed less in pesticides, than mosquitoes from the pristine sites. These results show that pesticide presence determines species distribution and impacts their behaviors and interactions.

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