Genetics,Synergists, and Age Affect Insecticide Sensitivity of the Honey Bee,Apis mellifera

The number of honey bee colonies in the United States has declined to half of its peak level in the 1940s, and colonies lost over the winter have reached levels that are becoming economically unstable. While the causes of these losses are numerous and the interaction between them is very complex, the role of insecticides has garnered much attention. As a result, there is a need to better understand the risk of insecticides to bees, leading to more studies on both toxicity and exposure. While much research has been conducted on insecticides and bees, there have been very limited studies to elucidate the role that bee genotype and age has on the toxicity of these insecticides. The goal of this study was to determine if there are differences in insecticide sensitivity between honey bees of different genetic backgrounds (Carniolan, Italian, and Russian stocks) and assess if insecticide sensitivity varies with age. We found that Italian bees were the most sensitive of these stocks to insecticides, but variation was largely dependent on the class of insecticide tested. There were almost no differences in organophosphate bioassays between honey bee stocks (<1-fold), moderate differences in pyrethroid bioassays (1.5 to 3-fold), and dramatic differences in neonicotinoid bioassays (3.4 to 33.3-fold). Synergism bioassays with piperonyl butoxide, amitraz, and coumaphos showed increased phenothrin sensitivity in all stocks and also demonstrated further physiological differences between stocks. In addition, as bees aged, the sensitivity to phenothrin significantly decreased, but the sensitivity to naled significantly increased. These results demonstrate the variation arising from the genetic background and physiological transitions in honey bees as they age. This information can be used to determine risk assessment, as well as establishing baseline data for future comparisons to explain the variation in toxicity differences for honey bees reported in the literature.     

Molecular and Kinetic Properties of Two Acetylcholinesterases from the Western Honey Bee,Apis mellifera

We investigated the molecular and kinetic properties of two acetylcholinesterases (AmAChE1 and AmAChE2) from the Western honey bee, Apis mellifera. Western blot analysis revealed that AmAChE2 has most of catalytic activity rather than AmAChE1, further suggesting that AmAChE2 is responsible for synaptic transmission in A. mellifera, in contrast to most other insects. AmAChE2 was predominately expressed in the ganglia and head containing the central nervous system (CNS), while AmAChE1 was abundantly observed not only in the CNS but also in the peripheral nervous system/non-neuronal tissues. Both AmAChEs exist as homodimers; the monomers are covalently connected via a disulfide bond under native conditions. However, AmAChE2 was associated with the cell membrane via the glycophosphatidylinositol anchor, while AmAChE1 was present as a soluble form. The two AmAChEs were functionally expressed with a baculovirus system. Kinetic analysis revealed that AmAChE2 has approximately 2,500-fold greater catalytic efficiency toward acetylthiocholine and butyrylthiocholine than AmAChE1, supporting the synaptic function of AmAChE2. In addition, AmAChE2 likely serves as the main target of the organophosphate (OP) and carbamate (CB) insecticides as judged by the lower IC₅₀ values against AmAChE2 than against AmAChE1. When OP and CB insecticides were pre-incubated with a mixture of AmAChE1 and AmAChE2, a significant reduction in the inhibition of AmAChE2 was observed, suggesting a protective role of AmAChE1 against xenobiotics. Taken together, based on their tissue distribution pattern, molecular and kinetic properties, AmAChE2 plays a major role in synaptic transmission, while AmAChE1 has non-neuronal functions, including chemical defense.     

Extreme Recombination Frequencies Shape Genome Variation and Evolution in the Honeybee,Apis mellifera

Meiotic recombination is a fundamental cellular process, with important consequences for evolution and genome integrity. However, we know little about how recombination rates vary across the genomes of most species and the molecular and evolutionary determinants of this variation. The honeybee, Apis mellifera, has extremely high rates of meiotic recombination, although the evolutionary causes and consequences of this are unclear. Here we use patterns of linkage disequilibrium in whole genome resequencing data from 30 diploid honeybees to construct a fine-scale map of rates of crossing over in the genome. We find that, in contrast to vertebrate genomes, the recombination landscape is not strongly punctate. Crossover rates strongly correlate with levels of genetic variation, but not divergence, which indicates a pervasive impact of selection on the genome. Germ-line methylated genes have reduced crossover rate, which could indicate a role of methylation in suppressing recombination. Controlling for the effects of methylation, we do not infer a strong association between gene expression patterns and recombination. The site frequency spectrum is strongly skewed from neutral expectations in honeybees: rare variants are dominated by AT-biased mutations, whereas GC-biased mutations are found at higher frequencies, indicative of a major influence of GC-biased gene conversion (gBGC), which we infer to generate an allele fixation bias 5 – 50 times the genomic average estimated in humans. We uncover further evidence that this repair bias specifically affects transitions and favours fixation of CpG sites. Recombination, via gBGC, therefore appears to have profound consequences on genome evolution in honeybees and interferes with the process of natural selection. These findings have important implications for our understanding of the forces driving molecular evolution.     

Nonsusceptibility of the Honey Bee,Apis mellifera (Hymenoptera: Apidae), to Steinernematid and Heterorhabditid Nematodes

We exposed honey bee workers and brood to four entomopathogenic nematode species under conditions normally encountered in the hive by spraying nematodes onto combs. Mortality of adult bees exposed to any of the nematode species was less than 10%, and there was no evidence of nematode infection when dead adults were dissected. To assess the impact of nematodes on brood, we used smaller-size honey combs placed in the second story (super) of a hive and large brood combs placed in the main section of the hive. Our results were inconsistent between these two experimental designs. The smaller honey combs sprayed with Steinernema carpocapsae contained the largest number of uncapped ceils, those sprayed with Heterorhabditis baeteriophora or S. riobravis contained an intermediate number of uncapped cells, and control combs and those sprayed with S. glaseri contained the fewest nmnber of uncapped cells. Large combs sprayed with S. riobravis contained more uncapped ceils than controls or those sprayed with S. carpocapsae, although the differences were not significant. Our results do not support the hypothesis that high-temperature-tolerant species of nematodes are necessarily more infective to honey bees.     

Gregarines Found in the Honey Bee Apis mellifera Linnaeus in Venezuela.

SUMMARY. Gregarines were found for the first time in the honey bee Apis mellifera L. in Venezuela. The parasites attacked the inner wall of the ventriculus of the adult bees, causing heavy losses in apiculture in October 1954 and June 1955. The disease produced was called gregarina disease of the honey bee (in Spanish "gregarinosis de la abeja").     

Linkage Map of the Honey Bee, Apis Mellifera, Based on Rapd Markers

A linkage map was constructed for the honey bee based on the segregation of 365 random amplified polymorphic DNA (RAPD) markers in haploid male progeny of a single female bee. The X locus for sex determination and genes for black body color and malate dehydrogenase were mapped to separate linkage groups. RAPD markers were very efficient for mapping, with an average of about 2.8 loci mapped for each 10-nucleotide primer that was used in polymerase chain reactions. The mean interval size between markers on the map was 9.1 cM. The map covered 3110 cM of linked markers on 26 linkage groups. We estimate the total genome size to be ~3450 cM. The size of the map indicated a very high recombination rate for the honey bee. The relationship of physical to genetic distance was estimated at 52 kb/cM, suggesting that map-based cloning of genes will be feasible for this species.     

The Bacterial Communities Associated with Honey Bee (Apis mellifera) Foragers

The honey bee is a key pollinator species in decline worldwide. As part of a commercial operation, bee colonies are exposed to a variety of agricultural ecosystems throughout the year and a multitude of environmental variables that may affect the microbial balance of individuals and the hive. While many recent studies support the idea of a core microbiota in guts of younger in-hive bees, it is unknown whether this core is present in forager bees or the pollen they carry back to the hive. Additionally, several studies hypothesize that the foregut (crop), a key interface between the pollination environment and hive food stores, contains a set of 13 lactic acid bacteria (LAB) that inoculate collected pollen and act in synergy to preserve pollen stores. Here, we used a combination of 454 based 16S rRNA gene sequencing of the microbial communities of forager guts, crops, and corbicular pollen and crop plate counts to show that (1) despite a very different diet, forager guts contain a core microbiota similar to that found in younger bees, (2) corbicular pollen contains a diverse community dominated by hive-specific, environmental or phyllosphere bacteria that are not prevalent in the gut or crop, and (3) the 13 LAB found in culture-based studies are not specific to the crop but are a small subset of midgut or hindgut specific bacteria identified in many recent 454 amplicon-based studies. The crop is dominated by Lactobacillus kunkeei, and Alpha 2.2 (Acetobacteraceae), highly osmotolerant and acid resistant bacteria found in stored pollen and honey. Crop taxa at low abundance include core hindgut bacteria in transit to their primary niche, and potential pathogens or food spoilage organisms seemingly vectored from the pollination environment. We conclude that the crop microbial environment is influenced by worker task, and may function in both decontamination and inoculation.     

Orientation-sensitive Neurons in the Brain of the Honey Bee (Apis mellifera)

Recent behavioural experiments have shown that bees are able to distinguish vertically presented patterns with orientation cues, although the locations of areas of black are randomized. To discriminate between two orientations, the bees must possess more than one orientation-sensitive neuron type. Therefore, the aim is to search for different types of orientation-sensitive cells of the honey bee, and measure their receptive field, velocity sensitivity and contrast sensitivity. Orientation-sensitive cells with two different types of orientation tuning-curves were recorded intracellularly in the mid-brain of the honey bee when the stimulus was a narrow bar (bar width = 5 degrees ). These cells are sensitive to bar movement within their large receptive field, which covers the visual field of one eye. They are quite distinct from the well-known directional motion detectors. The contrast sensitivity of the orientation-sensitive cells recorded in this study corresponds to results from behavioural experiments. The velocity-sensitivity curves of the orientation-sensitive cells differ from those of the direction-sensitive cells. Measurements of orientation sensitivity and contrast sensitivity when the stimulus is a wide bar (bar width = 10 degrees ), done in different eye regions, suggest that each orientation-sensitive cell receives visual signals from an array of orientational subunits within its receptive field. The correspondence between these physiological results and the results of recent behavioural experiments are discussed. Copyright 1997 Elsevier Science Ltd. All rights reserved     

A Locomotor Deficit Induced by Sublethal Doses of Pyrethroid and Neonicotinoid Insecticides in the Honeybee Apis mellifera

The toxicity of pesticides used in agriculture towards non-targeted organisms and especially pollinators has recently drawn the attention from a broad scientific community. Increased honeybee mortality observed worldwide certainly contributes to this interest. The potential role of several neurotoxic insecticides in triggering or potentiating honeybee mortality was considered, in particular phenylpyrazoles and neonicotinoids, given that they are widely used and highly toxic for insects. Along with their ability to kill insects at lethal doses, they can compromise survival at sublethal doses by producing subtle deleterious effects. In this study, we compared the bee’s locomotor ability, which is crucial for many tasks within the hive (e.g. cleaning brood cells, feeding larvae…), before and after an acute sublethal exposure to one insecticide belonging to the two insecticide classes, fipronil and thiamethoxam. Additionally, we examined the locomotor ability after exposure to pyrethroids, an older chemical insecticide class still widely used and known to be highly toxic to bees as well. Our study focused on young bees (day 1 after emergence) since (i) few studies are available on locomotion at this stage and (ii) in recent years, pesticides have been reported to accumulate in different hive matrices, where young bees undergo their early development. At sublethal doses (SLD_48h, i.e. causing no mortality at 48h), three pyrethroids, namely cypermethrin (2.5 ng/bee), tetramethrin (70 ng/bee), tau-fluvalinate (33 ng/bee) and the neonicotinoid thiamethoxam (3.8 ng/bee) caused a locomotor deficit in honeybees. While the SLD_48h of fipronil (a phenylpyrazole, 0.5 ng/bee) had no measurable effect on locomotion, we observed high mortality several days after exposure, an effect that was not observed with the other insecticides. Although locomotor deficits observed in the sublethal range of pyrethroids and thiamethoxam would suggest deleterious effects in the field, the case of fipronil demonstrates that toxicity evaluation requires information on multiple endpoints (e.g. long term survival) to fully address pesticides risks for honeybees. Pyrethroid-induced locomotor deficits are discussed in light of recent advances regarding their mode of action on honeybee ion channels and current structure-function studies.     

A SNP Based High-Density Linkage Map of Apis cerana Reveals a High Recombination Rate Similar to Apis mellifera

Background

The Eastern honey bee, Apis cerana Fabricius, is distributed in southern and eastern Asia, from India and China to Korea and Japan and southeast to the Moluccas. This species is also widely kept for honey production besides Apis mellifera. Apis cerana is also a model organism for studying social behavior, caste determination, mating biology, sexual selection, and host-parasite interactions. Few resources are available for molecular research in this species, and a linkage map was never constructed. A linkage map is a prerequisite for quantitative trait loci mapping and for analyzing genome structure. We used the Chinese honey bee, Apis cerana cerana to construct the first linkage map in the Eastern honey bee.

Results

F2 workers (N = 103) were genotyped for 126,990 single nucleotide polymorphisms (SNPs). After filtering low quality and those not passing the Mendel test, we obtained 3,000 SNPs, 1,535 of these were informative and used to construct a linkage map. The preliminary map contains 19 linkage groups, we then mapped the 19 linkage groups to 16 chromosomes by comparing the markers to the genome of A. mellfiera. The final map contains 16 linkage groups with a total of 1,535 markers. The total genetic distance is 3,942.7 centimorgans (cM) with the largest linkage group (180 loci) measuring 574.5 cM. Average marker interval for all markers across the 16 linkage groups is 2.6 cM.

Conclusion

We constructed a high density linkage map for A. c. cerana with 1,535 markers. Because the map is based on SNP markers, it will enable easier and faster genotyping assays than randomly amplified polymorphic DNA or microsatellite based maps used in A. mellifera.     

Intra-Patriline Variability in the Performance of the Vibration Signal and Waggle Dance in the Honey Bee, Apis mellifera

We examined intra-patriline behavioral plasticity in communication behavior by generating lifetime behavioral profiles for the performance of the vibration signal and waggle dance in workers which were the progeny of three unrelated queens, each inseminated with the semen of a single, different drone. We found pronounced variability within each patriline for the tendency to produce each signal, the ontogeny of signal performance, and the persistence with which individual workers performed the signals throughout their lifetimes. Within each patriline, the number of workers that performed each signal and the distribution of onset ages for each signal were significantly different. In each patriline, workers of all ages could perform vibration signals; vibration signal production began 3–5 d before waggle dancing; and some workers began performing waggle dances at ages typically associated with precocious foraging. Most workers vibrated and waggled only 1–2 d during their lifetimes, although each patriline contained some workers that performed the signal persistently for up to 8 or 9 d. We also found marked variability in signal performance among the three worker lineages examined. Because the vibration signal and waggle dance influence task performance, variability in signaling behavior within and between subfamilies may help to organize information flow and collective labor in honey bee colonies. Inter-patriline variability may influence the total number of workers from different partrilines that perform the signals, whereas intra-patriline variability may further fine-tune signal performance and the allocation of labor to a given set of circumstances. Although intra-patriline behavioral variability is assumed to be widespread in the social insects, our study is the first to document the extent of this variability for honey bee communication signals.     

Landscape Learning during Flight Ensures Homing in Honey Bee (Apis mellifera) Drones

Journal of Insect Behavior - The role of learning to navigate toward a specific location has been extensively studied in the foraging context of social hymenopteran females, which bring resources...     

Racial Differences in Division of Labor in Colonies of the Honey Bee (Apis mellifera)

We measured the age at onset of foraging in colonies derived from three races of European honey bees, Apis mellifera mellifera, Apis mellifera caucasica and Apis mellifera ligustica , using a cross-fostering design that involved six unrelated colonies of each race. There was a significant effect of the race of the introduced bees on the age at onset of foraging: cohorts of A. m. ligustica bees showed the earliest onset, regardless of the race of the colony they were introduced to. There also was a significant effect of the race of the host colony: cohorts of bees introduced into mellifera colonies showed the earliest onset of foraging, regardless of the race of the bees introduced. Significant inter-trial differences also were detected, primarily because of a later onset of foraging in trials conducted during the autumn (September–October). These results demonstrate differences among European races of honey bees in one important component of colony division of labor. They also provide a starting point for analyses of the evolution of division of labor under different ecological conditions.