Document Type

Restricted

Advisor

Philip Barnes

Publication Date

2020

Comments

This paper may only be accessed on the Connecticut College campus until May 15, 2022.

Abstract

Insecticide resistance is considered a standard model of microevolution, in which a strong selective pressure is applied to a population, resulting in a change in the frequency of alleles that confer resistance. 4,4’-dichlorodiphenyltrichloroethane (DDT), an organochlorine insecticide had been extensively used for over 60 years in order to control plant insect pests as well as insects that vector human diseases. However, increased use of DDT consequently resulted in the surge of insect resistance, an example of which is shown in various strains of Drosophila melanogaster. Research suggests that exposure to DDT exerts such strong selection pressure on the resistance genes that the development of resistance may have also resulted in incidental changes to other, closely linked genes (Dapkus and Merrell, 1977).

A study completed by Winn (2013) involved an analysis of the genetic changes that have occurred in mating preference between a DDT-resistant population (91R) and its unselected, wild type control population (91C). The purpose of this current study was to see if a similar pattern of behavioral isolation is found between the D. melanogaster strain ORC, and its resistant counterpart, ORR. (Exposure to DDT was discontinued for both 91R and ORR in 2012. Since then, the partial behavioral isolation between 91C and 91R has disappeared.) Additionally, the inheritance pattern of DDT resistance in the F1 between ORR and ORC was investigated. A previous study of F1 inheritance using 91R and 91C indicated probable partial dominance strongly favoring the nonresistance of 91C (Rosenthal, 2019). As a result, it was hypothesized that ORC would display complete or strong partial dominance over ORR, as well as behavioral isolation between ORC and ORR.

The results of this study indicate no behavioral isolation between ORC and ORR populations. It is speculated that this is because of one of two reasons: (1) that selection somehow reversed the coincidental behavioral effects from resistance, either through pleiotropic effects or modifier genes, as ORR has evolved back toward wild type, or (2) that behavioral isolation between the two populations never existed. Additionally, ORC displayed strong partial dominance over ORR.

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The views expressed in this paper are solely those of the author.