Dissertation

Behavioral and Biochemical Processing of Natural and Synthetic Xenobiotics in the Western Honey Bee Apis mellifera

Liao, Ling-Hsiu

2016

Overview

As a eusocial insect, Apis mellifera, the western honey bee, accomplishes many tasks, including acquisition of food, defense against enemies, and reproduction, through division of labor. In this dissertation, I examined whether honey bees also exploit division of labor in the detoxification of natural and synthetic xenobiotics. I approached this question from a behavioral perspective by assessing the extent to which foragers can detect and avoid natural and synthetic xenobiotics, and from a biochemical perspective, by determining how detoxification capacity changes with temporal polyethism and task allocation and by assessing whether the toxicity of xenobiotics may be enhanced or ameliorated in the presence of co-occurring compounds. From a biochemical perspective, sequencing the honey bee genome revealed that all major classes of detoxification enzymes are reduced in diversity relative to many other insect genomes, an observation that raised the possibility that honey bees may increase their biochemical versatility by adjusting detoxification activity according to age- and task-related division of labor. In this regard, while the contributions of cytochrome P450 monooxygenases to xenobiotic detoxification have been characterized to some extent, the role of carboxylesterases in detoxification of exogenous esters has not yet received attention. Using several natural esters as potential substrates, I investigated whether carboxylesterases, like some detoxifying P450s, vary in activity relative to caste differentiation and temporal polyethism. From a behavioral perspective, I conducted a semi-field experiment to determine how free-flying foragers respond to natural and synthetic xenobiotics when alternate food is available. Some natural xenobiotics found in honey and beebread, derived from nectar and pollen respectively, have been shown to upregulate genes encoding proteins associated with detoxification and immunity and may thus potentially improve honey bee health. In contrast, most synthetic organic compounds used in agriculture are associated with a diverse array of adverse physiological consequences and are regarded as significant factors contributing to population declines. Accordingly, I conducted a series of bioassays to determine if foragers display any ability to recognize and respond positively to potentially beneficial phytochemicals and/or to discriminate against harmful synthetic xenobiotics to reduce colony exposure to toxins. Because certain phytochemicals—notably, some flavonols and phenolic acids—are almost invariably present in pollen irrespective of plant source, they are ubiquitous in the diet of honey bees. Just as folivorous insect species may come to rely on phytochemicals that are regularly encountered in their host plants for ecological and physiological functions, honey bees may also depend on some of these ubiquitous dietary phytochemicals and their absence from the diet may have effects that are as yet undetermined. One such physiological function played by these phytochemicals is upregulation of detoxification enzymes; their presence or absence may thus affect the toxicity of ingested xenobiotics. In order to clarify the impacts of common dietary phytochemicals on bees, I conducted a series of longevity assays with one-day-old adult honey bees to test if natural xenobiotics (phytochemicals from nectar) enhance honey bee worker longevity and detoxification capacity. Finally, to characterize the likelihood that dietary phytochemicals may ameliorate toxicity of co-occurring pesticides during foraging under field conditions, I combined survivorship assays with flight performance assays using a flight treadmill in order to ascertain whether mortality may be reduced via phytochemical modification of energy-linked mitochondrial metabolism and energy production.

• Publisher: ProQuest Dissertations & Theses
• Subject: Entomology
• ISBN: 9781369828979, 1369828977