Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Percival-Smith, Anthony

Abstract

Drosophila melanogaster can mimic qualities of honeybee altruism mediated by queen mandibular pheromone (QMP), a honeybee pheromone, which includes suppression of oogenesis and chemotactic attraction of males to sources of QMP. In this study, I assessed chemotaxis to the components of synthetic QMP (sQMP): the phenols; methyl-p-hydroxybenzoate (HOB) and 4-hydroxy-3-methoxyphenylethanol (HVA), and decenoic acids; 9-hydroxy-decenoic acid (9-HDA) and 9-oxo-decenoic acid (9-ODA). I found that the chemotactic response to these components is sexually dimorphic and they have complex interactions with one another. I conducted a screen to inhibit olfactory receptor neurons (ORN) using tetanus toxin (TeTx) and OrGAL4 drivers. Of the fifty-four ORs and eight ionotropic receptors (IRs) screened, I identified fourteen candidate receptors required for the chemotactic behavior. By inhibiting transmission of Or47b or Or94b neurons, I found that phenols have a role in anti-ovarian response to sQMP. These discoveries help advance our knowledge of honeybee QMP detection in Drosophila.

Summary for Lay Audience

Honeybee colonies have two female castes: the workers and the queen bee. The queen is fertile whereas workers are not. The workers groom and feed the queen as well as maintain her progeny and the colony. The social structure of the hive with distinct female castes is maintained by the queen mandibular pheromone (QMP), which is secreted exclusively from the mandibular glands of the queen. QMP inhibits development of ovaries in worker bees; such that only the queen is capable of reproduction. QMP also induces a retinue response in workers, which is a licking and grooming behavior geared towards the queen. In addition, presence of QMP attracts the males (drones) to the queen. The major chemical components of QMP are two phenols methyl-hydroxybenzoate (HOB), hydroxy-methoxyphenylethanol (HVA) and two decenoic acids 9 oxo-decenoic acid (9-ODA) and 9-hydroxy-decenoic acid (9-HDA). The mechanism of QMP function is challenging to study in honeybees because we lack sophisticated genetic tools to study them. However, recent findings have shown that Drosophila, the common fruit fly also responds to sQMP, in a similar manner as honeybees i.e., reduction in number of eggs in females and attraction of males to sQMP. This is a noteworthy response by itself, and can be exploited in the well-characterized genetic system of Drosophila. In this study, I investigate how a non-eusocial insect like Drosophila “smell” sQMP and its components using a simple T-maze to assess attraction/repulsion of fruit flies. I found that responses to these components were different in males and females, and the constituent chemicals interacted with one another. Studies have shown that olfactory receptors (ORs), are responsible for receiving odors and consequently receive the odor of QMP + its components. I have identified fourteen olfactory receptors that are required for detecting the components of QMP. I also found that when certain olfactory receptors were inhibited, a role for the phenolic components of sQMP in suppression of oogenesis was discovered. These findings are important in expanding our knowledge of how QMP is received in Drosophila and also in honeybees due to the evolutionary conservation of the response to QMP.

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