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PubMed2003

Study of temperature-growth interactions of entomopathogenic fungi with potential for control of Varroa destructor (Acari: Mesostigmata) using a nonlinear model of poikilotherm development.

AIMS: To investigate the thermal biology of entomopathogenic fungi being examined as potential microbial control agents of Varroa destructor, an ectoparasite of the European honey bee Apis mellifera. METHODS AND RESULTS: Colony extension rates were measured at three temperatures (20, 30 and 35 degrees C) for 41 isolates of entomopathogenic fungi. All of the isolates grew at 20 and 30 degrees C but only 11 isolates grew at 35 degrees C. Twenty-two isolates were then selected on the basis of appreciable growth at 30-35 degrees C (the temperature range found within honey bee colonies) and/or infectivity to V. destructor, and their colony extension rates were measured at 10 temperatures (12.5-35 degrees C). This data were then fitted to Schoolfield et al. [J Theor Biol (1981)88:719-731] re-formulation of the Sharpe and DeMichele [J Theor Biol (1977)64:649-670] model of poikilotherm development. Overall, this model accounted for 87.6-93.9% of the data variance. Eleven isolates exhibited growth above 35 degrees C. The optimum temperatures for extension rate ranged from 22.9 to 31.2 degrees C. Only three isolates exhibited temperature optima above 30 degrees C. The super-optimum temperatures (temperature above the optimum at which the colony extension rate was 10% of the maximum rate) ranged from 31.9 to 43.2 degrees C. CONCLUSIONS: The thermal requirements of the isolates examined against V. destructor are well matched to the temperatures in the broodless areas of honey bee colonies, and a proportion of isolates, should also be able to function within drone brood areas. SIGNIFICANCE AND IMPACT OF THE STUDY: Potential exists for the control of V. destructor with entomopathogenic fungi in honey bee colonies. The methods employed in this study could be utilized in the selection of isolates for microbial control prior to screening for infectivity and could help in predicting the activity of a fungal control agent of V. destructor under fluctuating temperature conditions.

Acari↗
PubMed1980

[Studies on potassium transport through glial cell membranes (author's transl)].

The retina of the honeybee drone is used as a model for the study of ion movements across the membranes of the glial cells caused by changes in the extracellular potassium concentration. The values found for changes in extracellular potential suggest that at least some of the potassium that enters glial cells in an active region of tissue is associated with an efflux of potassium from parts of the glial syncytium not affected by an increase in extracellular potassium concentration. In addition, it appears that ions other than K+ cross the glial membrane.

Animals↗
PubMed2003

Social exploitation of vitellogenin.

Vitellogenin is a female-specific glucolipoprotein yolk precursor produced by all oviparous animals. Vitellogenin expression is under hormonal control, and the protein is generally synthesized directly before yolk deposition. In the honeybee (Apis mellifera), vitellogenin is not only synthesized by the reproductive queen, but also by the functionally sterile workers. In summer, the worker population consists of a hive bee group performing a multitude of tasks including nursing inside the nest, and a forager group specialized in collecting nectar, pollen, water, and propolis. Vitellogenin is synthesized in large quantities by hive bees. When hive bees develop into foragers, their juvenile hormone titers increase, and this causes cessation of their vitellogenin production. This inverse relationship between vitellogenin synthesis and juvenile hormone is opposite to the norm in insects, and the underlying proximate processes and life-history reasons are still not understood. Here we document an alternative use of vitellogenin by showing that it is a source for the proteinaceous royal jelly that is produced by the hive bees. Hive bees use the jelly to feed larvae, queen, workers, and drones. This finding suggests that the evolution of a brood-rearing worker class and a specialized forager class in an advanced eusocial insect society has been directed by an alternative utilization of yolk protein.

Animals↗
PubMed2003

New components of the honey bee (Apis mellifera L.) queen retinue pheromone.

The honey bee queen produces pheromones that function in both releaser and primer roles such as attracting a retinue of workers around her, attracting drones on mating flights, preventing workers from reproducing at the individual (worker egg-laying) and colony (swarming) level, and regulating several other aspects of colony functioning. The queen mandibular pheromone (QMP), consisting of five synergistic components, is the only pheromone chemically identified in the honey bee (Apis mellifera L.) queen, but this pheromone does not fully duplicate the pheromonal activity of a full queen extract. To identify the remaining unknown compounds for retinue attraction, honey bee colonies were selectively bred to have low response to synthetic QMP and high response to a queen extract in a laboratory retinue bioassay. Workers from these colonies were then used in the bioassay to guide the isolation and identification of the remaining active components. Four new compounds were identified from several glandular sources that account for the majority of the difference in retinue attraction between synthetic QMP and queen extract: methyl (Z)-octadec-9-enoate (methyl oleate), (E)-3-(4-hydroxy-3-methoxyphenyl)-prop-2-en-1-ol (coniferyl alcohol), hexadecan-1-ol, and (Z9,Z12,Z15)-octadeca-9,12,15-trienoic acid (linolenic acid). These compounds were inactive alone or in combination, and they only elicited attraction in the presence of QMP. There was still unidentified activity remaining in the queen extract. The queen therefore produces a synergistic, multiglandular pheromone blend of at least nine compounds for retinue attraction, the most complex pheromone blend known for inducing a single behavior in any organism.

Animals↗
PubMed1988

Honeybee retinal glial cells transform glucose and supply the neurons with metabolic substrate.

The retina of the honeybee drone is a nervous tissue in which glial cells and photoreceptor cells (sensory neurons) constitute two distinct metabolic compartments. Retinal slices incubated with 2-deoxy[3H]glucose convert this glucose analogue to 2-deoxy[3H]glucose 6-phosphate, but this conversion is made only in the glial cells. Hence, glycolysis occurs only in glial cells. In contrast, the neurons consume O2 and this consumption is sustained by the hydrolysis of glycogen, which is contained in large amounts in the glia. During photostimulation the increased oxidative metabolism of the neurons is sustained by a higher supply of carbohydrates from the glia. This clear case of metabolic interaction between neurons and glial cells supports Golgi's original hypothesis, proposed nearly 100 years ago, about the nutritive function of glial cells in the nervous system.

Animals↗
PubMed1993

Bee venom hyaluronidase is homologous to a membrane protein of mammalian sperm.

The venom of honeybees, Apis mellifera, contains several biologically active peptides and two enzymes, one of which is a hyaluronidase. By using degenerate oligonucleotides derived from the amino-terminal sequence of this hyaluronidase reported by others, clones encoding the precursor for this enzyme could be isolated from a cDNA library prepared from venom glands of worker bees. The deduced amino acid sequence showed that bee venom hyaluronidase is a polypeptide composed of 349 amino acids containing four cysteines and three potential sites for N-glycosylation. The sequence of the precursor also indicated that the conversion of the pro-enzyme to the end product must involve cleavage of a Thr-Pro bond, a most unusual processing reaction. The mRNA encoding hyaluronidase could also be detected in testes from drones. Expression of the cloned cDNA in Escherichia coli yielded a 41-kDa polypeptide that had hyaluronidase activity. Interestingly, the hyaluronidase from bee venom glands exhibited significant homology to PH-20, a membrane protein of guinea pig sperm involved in sperm-egg adhesion. These structural data support the long-held view that hyaluronidases play a role in fertilization.

Acrosome↗
PubMed2006

Quantitative comparison of caste differences in honeybee hemolymph.

The honeybee, Apis mellifera, is an invaluable partner in agriculture around the world both for its production of honey and, more importantly, for its role in pollination. Honeybees are largely unexplored at the molecular level despite a long and distinguished career as a model organism for understanding social behavior. Like other eusocial insects, honeybees can be divided into several castes: the queen (fertile female), workers (sterile females), and drones (males). Each caste has different energetic and metabolic requirements, and each differs in its susceptibility to pathogens, many of which have evolved to take advantage of the close social network inside a colony. Hemolymph, arthropods' equivalent to blood, distributes nutrients throughout the bee, and the immune components contained within it form one of the primary lines of defense against invading microorganisms. In this study we have applied qualitative and quantitative proteomics to gain a better understanding of honeybee hemolymph and how it varies among the castes and during development. We found large differences in hemolymph protein composition, especially between larval and adult stage bees and between male and female castes but even between adult workers and queens. We also provide experimental evidence for the expression of several unannotated honeybee genes and for the detection of biomarkers of a viral infection. Our data provide an initial molecular picture of honeybee hemolymph, to a greater depth than previous studies in other insects, and will pave the way for future biochemical studies of innate immunity in this animal.

Algorithms↗
PubMed2004

Towards a common neural substrate in the immediate and effective inhibition of stuttering.

Stuttering can be effectively inhibited via exogenous sensory signals (e.g., speaking in unison or using altered auditory feedback) or by using endogenous motoric strategies (e.g., singing or therapeutically implementing long vowel prolongations to reduce speech rates). We propose that these channels, which superficially appear to be diametrically opposite, centrally converge in the engagement of mirror neurons for fluent gestural productions. Sensory changes incurred via exogenous speech signals allow for direct engagement of mirror systems, while endogenous motor strategies appear to require significant departures from normal speech production (e.g., highly unnatural or droned speech) to engage mirror systems. Thus, paradoxically, stuttering is prone to resurface during attempts to impose naturalness upon therapeutic speech.

Feedback↗
PubMed1992

The nss mutation or lanthanum inhibits light-induced Ca2+ influx into fly photoreceptors.

Ion-selective calcium microelectrodes were inserted into the compound eyes of the wild-type sheep blowfly Lucilia or into the retina of the no steady state (nss) mutant of Lucilia. These electrodes monitored light-induced changes in the extracellular concentration of calcium (delta[Ca2+]o) together with the extracellularly recorded receptor potential. Prolonged dim lights induced a steady reduction in [Ca2+]o during light in the retina of normal Lucilia, while relatively little change in [Ca2+]o was observed in the retina of the nss mutant. Prolonged intense light induced a multiphasic change in [Ca2+]o: the [Ca2+]o signal became transient, reaching a minimum within 6 s after light onset, and then rose to a nearly steady-state phase below the dark concentration. When lights were turned off, a rapid increase in [Ca2+]o was observed, reaching a peak above the dark level and then declining again to the dark level within 1 min. In analogy to similar studies conduced in the honeybee drone, we suggest that the reduction in [Ca2+]o reflects light-induced Ca2+ influx into the photoreceptors, while the subsequent increase in [Ca2+]o reflects the activation of the Na-Ca exchange which extrudes Ca2+ from the cells. In the nss mutant in response to intense prolonged light, the receptor potential declines to baseline during light while the Ca2+ signal is almost abolished, revealing only a short transient reduction in [Ca2+]o. Application of lanthanum (La3+), but not nickel (Ni2+), into the retinal extracellular space of normal Lucilia mimicked the effect of the nss mutation on the receptor potential, while complete elimination of the Ca2+ signal in a reversible manner was observed. The results suggest that La3+ and the nss mutation inhibit light-induced Ca2+ influex into the photoreceptor in a manner similar to the action of the trp mutation in Drosophila, which has been shown to block specifically a light-activated Ca2+ channel necessary to maintain light excitation.

Animals↗
PubMed1969

Effects of sodium, potassium, and calcium ions on slow and spike potentials in single photoreceptor cells.

The influence of changes in the ionic composition of the bathing medium on responses of the retinula cell of the honeybee drone to light was examined by means of intracellular microelectrodes. The resting potential of the cell was influenced mainly by the concentration of K. The peak of the receptor potential (the transient), which in a normal solution and with strong light approaches zero membrane potential, overshot this level in a K-rich solution. An increase in the concentration of K also raised the level of the steady-state phase of the receptor potential (the plateau). The amplitude of the receptor potential was decreased and the spike potential rapidly abolished when Na was replaced by either sucrose, choline, or Tris. In a Ca-free solution the amplitude of the response and especially that of the plateau, was increased. An increase in Ca had the opposite effects. All these changes were reversible. An attempt was made to interpret the receptor and spike potentials in terms of passive movements of Na and K across the membrane of the retinula cell. The major difficulty encountered was to find an explanation for the persistence of an appreciable fraction of the transient and the plateau in preparations kept up to 12 hr in a solution in which all the Na had been replaced by choline, Tris, or sucrose.

Animals↗
PubMed1991

The light-induced increase of carbohydrate metabolism in glial cells of the honeybee retina is not mediated by K+ movement nor by cAMP.

The retina of the honeybee drone is a nervous tissue in which glial cells and photoreceptor neurons constitute two distinct metabolic compartments. The phosphorylation of glucose and its subsequent incorporation into glycogen occur essentially in glia, whereas O2 consumption occurs in the photoreceptors. After [3H] glucose loading of superfused retinal slices, light stimulation induced a significant rise in [3H] glycogen turnover in the glia. This occurs without a concomitant covalent modification of glycogen enzymes. Probably only an increase or a decrease of the availability of [3H] glycosyls that are incorporated into glycogen is necessary. As only photoreceptors are directly excitable by light, we searched for a signal that stimulates glycogen metabolism in the glia. Although K+ in extracellular space and glia increases after repetitive light stimulation, increasing bath K+ in the dark did not mimic the metabolic effects of light, despite an equivalent increase of K+ in the extracellular space and glia. We subsequently explored the role of cAMP, a universal intracellular second messenger. Exposure of retinal slices to the adenylate-cyclase activator forskolin induced an expected increase in the rate of formation of cAMP, but only partially mimicked the metabolic effects of light. Furthermore, light stimulation failed to induce a rise in the rate of formation of cAMP. We conclude that in this nervous system, without synapses, neither K+ nor cAMP mediates the effect of light stimulation on intraglial glucose metabolism.

Animals↗
PubMed2002

The pollination mechanism in Trigonidium obtusum Lindl (Orchidaceae: Maxillariinae): sexual mimicry and trap-flowers.

The pollination process in Trigonidium obtusum Lindl. (Epidendroideae: Maxillariinae) is documented. The flowers are pollinated by sexually excited drones of Plebeia droryana (Meliponinae). When attempting to copulate either with sepals or petals, these bees slip on the waxy perianth surface and become trapped in the funnel-like flower tube. Bees trying to escape from the flowers may instead access the space between the column and lip, fixing the pollinarium on their scutellum. Pollinarium-bearing bees may pollinate the flowers when repeating the above-mentioned steps, leaving pollinia on the concave stigmatic surface, thus effecting pollination. Recently removed pollinaria are too broad to enter the stigma but they begin to dehydrate and within 40 min of removal are small enough to fit the stigmatic cavity. This mechanism prevents insect-mediated self-pollination and promotes cross-pollination. Preliminary evidence based on experiments with cultivated plants suggests that they are self-compatible but that fruit set is pollinator-dependent. The data obtained are discussed in a phylogenetic context. It is suggested that the pseudocopulatory syndrome in Trigonidium could have evolved from rewardless (food advertising) ancestors. Pseudocopulation in the context of the long flowering period of this orchid species (about 7 months) is understandable since the eusocial Plebeia bees produce fertile individuals several times a year.

Animals↗
PubMed2004

Sexual mimicry in Mormolyca ringens (Lindl.) Schltr. (Orchidaceae: Maxillariinae).

BACKGROUND AND AIMS: Pollination through sexual mimicry, also known as pseudocopulation, has been suggested to occur in some genera of the Neotropical orchid subtribe Maxillariinae. However, it has been demonstrated so far only for Trigonidium obtusum. This study reports and illustrates pollination through sexual mimicry in Mormolyca ringens. METHODS: A total of 70 h were dedicated to the observation of flowers and pollinator behaviour, which was photographically recorded. Flower features involved in pollinator attraction were studied using a stereomicroscope and by SEM analyses. Preliminary observations on the plant breeding system were made by manually self-pollinating flowers. The chemical composition of the fragrance volatiles was determined by GC/MS analysis. KEY RESULTS: The flower features of M. ringens parallel those of other pseudocopulatory flowers. The labellum shape and indument are reminiscent of an insect. Sexually excited drones of Nannotrigona testaceicornis and Scaptotrigona sp. (both in the Apidae: Meliponini) attempt copulation with the labellum and pollinate the flower in the process. In both bee species, the pollinarium is attached to the scutellum. Pollinator behaviour may promote some degree of self-pollination, but preliminary observations indicate that M. ringens flowers are self-incompatible. Flowers are produced all the year round, which ties in with the production of bee males several times a year. The phylogenetic relationships of M. ringens are discussed and a number of morphological and phenological features supporting them are reported. CONCLUSIONS: It is expected that further research could bring to light whether other Maxillariinae species are also pollinated through sexual mimicry. When a definitive and robust phylogeny of this subtribe is available, it should be possible to determine how many times pseudocopulation evolved and its possible evolutionary history.

Breeding↗
PubMed1990

Parental analysis of introgressive hybridization between African and European honeybees using nuclear DNA RFLPs.

African honeybees, introduced into Brazil 33 years ago, have spread through most of South and Central America and have largely replaced the extant European bees. Due to a paucity of genetic markers, genetic interactions between European and African bees are not well understood. Three restriction fragment length polymorphisms (RFLPs), detected with random, nuclear DNA probes, are described. The polymorphisms are specific to bees of European descent, possibly specific to certain European races. Each European marker was found present at a high frequency in U.S. colonies but absent in South African bees. Previous mitochondrial DNA studies of neotropical bees have revealed negligible maternal gene flow from managed European apiaries into feral African populations. The findings reported here with nuclear DNA show paternal gene flow between the two but suggest asymmetries in levels of introgressive hybridization. Managed colonies in southern Mexico, derived from European maternal lines, showed diminished levels of the European nuclear markers, reflecting significant hybridization with African drones. The European alleles were present only at low frequencies in feral swarms from the same area. The swarms were of African maternal descent. In Venezuelan colonies, also derived from African maternal lines, the European markers were almost totally absent. The results point to limited paternal introgression from European colonies into the African honeybee populations. These findings dispute other views regarding modes of Africanization.

Africa↗
PubMedDate not supplied

Characterization of honeybee (Apis mellifera L.) chromosomes using repetitive DNA probes and fluorescence in situ hybridization.

Two different repetitive DNA probes of Apis mellifera and ribosomal DNA from Drosophila melanogaster were used to characterize the chromosomal set of the honeybee (n = 16). The probes were hybridized to chromosome preparations of haploid testis tissue from drone larvae using fluorescence in situ hybridization (FISH). The honeybee probes hybridized to the telomeric (Alu I family) and centromeric region (Ava I family) of most chromosomes. The rDNA probe labeled two chromosomes only. Combination of the three probes yielded labeled patterns allowing us to identify each chromosome of the honeybee individually. This is the first report of an unambiguous identification of the chromosomal set of the honeybee, since classical banding techniques failed to yield clear patterns for identification. The consensus sequence of the centromeric reiterated probe (Ava I family) has a length of about 550 nucleotides and shows no homology to other known sequences. However, the structural organization of a 130-nucleotides long motif forming the unusually homogeneous 550 nucleotides repeat is similar to those found in mammals' repetitive DNAs.

Animals↗
PubMed2006

Full counting statistics for a single-electron transistor: nonequilibrium effects at intermediate conductance.

We evaluate the current distribution for a single-electron transistor with intermediate strength tunnel conductance. Using the Schwinger-Keldysh approach and the drone (Majorana) fermion representation, we account for the renormalization of system parameters. Nonequilibrium effects induce a lifetime broadening of the charge-state levels, which suppress large current fluctuations.

Journal Article↗
PubMed2002

The Africanization of honeybees (Apis mellifera L.) of the Yucatan: a study of a massive hybridization event across time.

Until recently, African and European subspecies of the honeybee (Apis mellifera L.) had been geographically separated for around 10,000 years. However, human-assisted introductions have caused the mixing of large populations of African and European subspecies in South and Central America, permitting an unprecedented opportunity to study a large-scale hybridization event using molecular analyses. We obtained reference populations from Europe, Africa, and South America and used these to provide baseline information for a microsatellite and mitochondrial analysis of the process of Africanization of the bees of the Yucatan Peninsula, Mexico. The genetic structure of the Yucatecan population has changed dramatically over time. The pre-Africanized Yucatecan population (1985) comprised bees that were most similar to samples from southeastern Europe and northern and western Europe. Three years after the arrival of Africanized bees (1989), substantial paternal gene flow had occurred from feral Africanized drones into the resident European population, but maternal gene flow from the invading Africanized population into the local population was negligible. However by 1998, there was a radical shift with both African nuclear alleles (65%) and African-derived mitochondria (61%) dominating the genomes of domestic colonies. We suggest that although European mitochondria may eventually be driven to extinction in the feral population, stable introgression of European nuclear alleles has occurred.

Africa↗
PubMed2004

Neuron-glial trafficking of NH4+ and K+: separate routes of uptake into glial cells of bee retina.

Ammonium (NH4+ and/or NH3) and K+ are released from active neurons and taken up by glial cells, and can modify glial cell behaviour. Study of these fluxes is most advanced in the retina of the honeybee drone, which consists essentially of identical neurons (photoreceptors) and identical glial cells (outer pigment cells). In isolated bee retinal glial cells, ammonium crosses the membrane as NH4+ on a Cl- cotransporter. We have now investigated, in the more physiological conditions of a retinal slice, whether the NH4+-Cl- cotransporter can transport K+ and whether the major K+ conductance can transport NH4+. We increased [NH4+] or [K+] in the superfusate and monitored uptake by recording from the glial cell syncytium or from interstitial space with microelectrodes selective for H+ or K+. In normal superfusate solution, ammonium acidified the glial cells but, after 6 min superfusion in low [Cl-] solution, ammonium alkalinized them. In the same low [Cl-] conditions, the rise in intraglial [K+] induced by an increase in superfusate [K+] was unchanged, i.e. no K+ flux on the Cl- cotransporter was detected. Ba2+ (5 mm) abolished the glial depolarization induced by K+ released from photoreceptors but did not reduce NH4+uptake. We estimate that when extracellular [NH4+] is increased, 62-100% is taken up by the NH4+-Cl- cotransporter and that when K+ is increased, 77-100% is taken up by routes selective for K+. This separation makes it possible that the glial uptake of NH4+ and of K+, and hence their signalling roles, might be regulated separately.

Animals↗