Abstract
BackgroundThe Hunt bumble bee (Bombus huntii Greene, Hymenoptera: Apidae) is a holometabolous, social insect important as a pollinator in natural and agricultural ecosystems in western North America. Bumble bees spend a significant amount of time foraging on a wide variety of flowering plants, and this activity exposes them to both plant toxins and pesticides, posing a threat to individual and colony survival. Little is known about what detoxification pathways are active in bumble bees, how the expression of detoxification genes changes across life stages, or how the number of detoxification genes expressed in B. huntii compares to other insects.ResultsWe found B. huntii expressed at least 584 genes associated with detoxification and stress responses. The expression levels of some of these genes, such as those encoding the cytochrome P450s, glutathione S-transferases (GSTs) and glycosidases, vary among different life stages to a greater extent than do other genes. We also found that the number of P450s, GSTs and esterase genes expressed by B. huntii is similar to the number of these genes found in the genomes of other bees, namely Bombus terrestris, Bombus impatiens, Apis mellifera and Megachile rotundata, but many fewer than are found in the fly Drosophila melanogaster.ConclusionsBombus huntii has transcripts for a large number of detoxification and stress related proteins, including oxidation and reduction enzymes, conjugation enzymes, hydrolytic enzymes, ABC transporters, cadherins, and heat shock proteins. The diversity of genes expressed within some detoxification pathways varies among the life stages and castes, and we typically identified more genes in the adult females than in larvae, pupae, or adult males, for most pathways. Meanwhile, we found the numbers of detoxification and stress genes expressed by B. huntii to be more similar to other bees than to the fruit fly. The low number of detoxification genes, first noted in the honey bee, appears to be a common phenomenon among bees, and perhaps results from their symbiotic relationship with plants. Many flowering plants benefit from pollinators, and thus offer these insects rewards (such as nectar) rather than defensive plant toxins.
Highlights
The Hunt bumble bee (Bombus huntii Greene, Hymenoptera: Apidae) is a holometabolous, social insect important as a pollinator in natural and agricultural ecosystems in western North America
Bees are exposed to toxic substances in the environment, such as pesticides, phytochemicals, microbial toxins, pollutants and other xenobiotics [6,7,8], but genomic analyses of the honey bee, A. mellifera, found fewer detoxification genes than are present in D. melanogaster and A. gambiae [4,9]. To determine if this phenomenon is common among bees or unique to the honey bee, we evaluated the expression of detoxification and stress related genes in a common western North American bumble bee, Bombus huntii
An overview of detoxification and stress response genes in B. huntii We developed a cDNA database of 102,778 contigs and singletons using pyrosequencing of messenger RNA (mRNA) extracted from eggs, larvae, pupae, adult workers, adult males, an egglaying queen, and a diapausing queen of B. huntii
Summary
The Hunt bumble bee (Bombus huntii Greene, Hymenoptera: Apidae) is a holometabolous, social insect important as a pollinator in natural and agricultural ecosystems in western North America. In addition to pesticide resistance, detoxification and stress responses are important adaptations that allow insects to overcome the chemical defenses of the plants and animals they feed on Genes associated with these responses have been identified in many insects, including the mosquitoes Anopheles gambiae [1] and Aedes aegypti [2], the fruit fly Drosophila melanogaster [3], the mellifera, B. huntii is a social insect with a diet based on pollen and nectar from a broad array of plants, so environmental exposures to xenobiotics should be similar. Many cytochrome P450s are important enzymes for catalyzing oxidation-reduction reactions, and they are probably important for pesticide detoxification in A. mellifera [13]; reactive oxygen species (ROS), such as hydrogen peroxide, hydroxyl radicals, and superoxides, are typical by-products of these reactions. Cytochrome P450s are involved in the production of pheromones, ecdysteroids and juvenile hormones [14,15,16], and many of the enzymes that breakdown ROS are associated with breaking down by-products from metabolism
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