Ultrastructure of the midgut of the worker honey bee Apis mellifera heavily infected with Nosema apis

Midgut epithelial cells from healthy bees possessed numerous mitochondria, strands of endoplasmic reticulum, evenly distributed ribosomes, zymogen granules, and two kinds of lipid inclusions. In heavily infected midguts of honey bees, Apis mellifera, all epithelial cells were observed to be infected with Nosema apis. Cells of the entire midgut were packed with mature spores and, in some cases, mixed with immature stages. Spores were not found among cells of the brush border and basal infolding. Muscle cells and tracheal end cells of the midgut were not infected. The cytoplasm of the infected cell contained a large number of vacuoles, numerous large inclusion bodies, and aggregated ribosomes. Signs of extensive lysis were observed within the heavily infected cells, although the cell membranes were intact.     

Four quantitative trait loci that influence worker sterility in the honeybee (Apis mellifera)

The all-female worker caste of the honeybee (Apis mellifera) is effectively barren in that workers refrain from laying eggs in the presence of a fecund queen. The mechanism by which workers switch off their ovaries in queenright colonies is pheromonally cued, but there is genetically based variation among individuals: some workers have high thresholds for ovary activation, while for others the response threshold is lower. Genetic variation for threshold response by workers to ovary-suppressing cues is most evident in "anarchist" colonies in which mutant patrilines have a proportion of workers that activate their ovaries and lay eggs, despite the presence of a queen. In this study we use a selected anarchist line to create a backcross queenright colony that segregated for high and low levels of ovary activation. We used 191 informative microsatellite loci, covering all 16 linkage groups to identify QTL for ovary activation and test the hypothesis that anarchy is recessively inherited. We reject this hypothesis, but identify four QTL that together explain approximately 25% of the phenotypic variance for ovary activation in our mapping population. They provide the first molecular evidence for the existence of quantitative loci that influence selfish cheating behavior in a social animal.     

Free fatty acids digested from pollen and triolein in the honeybee (Apis mellifera carnica Pollmann) midgut

Honey bees satisfy their lipid requirement by consuming pollen. The free fatty acid content of the midgut was used to quantify fat digestion. Midguts extracted from younger workers of known ages and from foragers were divided into three components: endoperitrophic region (peritrophic membrane with gut contents), extraperitrophic region and intestinal wall. Both the total amount of pollen and the amount of free fatty acids in the endoperitrophic region and in the intestinal wall depend on the bee's age. The amounts increase within the 1st 3 days of a honey bee's life, reach maxima around the age of 8 days and then decrease continuously to the lowest values, measured in forager bees. Forced feeding with triacylglycerol results in significantly higher levels of free fatty acids, especially in the endoperitrophic region, in 8-day-old bees and foragers. This indicates that lipolytic activity depends on age and that the free fatty acid content in 8-day-old bees is primarily limited by the amount and availability of lipids ingested. The results show further that fat digestion depends on the functional status of honey bees, as is the case for pollen consumption, speed of transport of pollen bolus through the alimentary canal and protein digestion.     

Lethal infection thresholds of Paenibacillus larvae for honeybee drone and worker larvae (Apis mellifera)

We compared the mortality of honeybee (Apis mellifera) drone and worker larvae from a single queen under controlled in vitro conditions following infection with Paenibacillus larvae, a bacterium causing the brood disease American Foulbrood (AFB). We also determined absolute P. larvae cell numbers and lethal titres in deceased individuals of both sexes up to 8 days post infection using quantitative real‐time PCR (qPCR). Our results show that in drones the onset of infection induced mortality is delayed by 1 day, the cumulative mortality is reduced by 10% and P. larvae cell numbers are higher than in worker larvae. Since differences in bacterial cell titres between sexes can be explained by differences in body size, larval size appears to be a key parameter for a lethal threshold in AFB tolerance. Both means and variances for lethal thresholds are similar for drone and worker larvae suggesting that drone resistance phenotypes resemble those of related workers.     

A note on the preservation of chromatic information in the lamina of the worker honeybee (Apis mellifera)

Summary Extracellular recordings were taken from a sustained unit in the first optic chiasma of the optic lobe of the worker honeybee. This unit received information from onlyone of the four retinal photopigments, despite the anatomical convergence in the retina and lamina ganglionaris.Supported by AFOSR contract F44620-70-C-0113 and NSF grant GB 30732.     

Hygropreference and brood care in the honeybee (Apis mellifera)

Terrestrial organisms need to limit evaporation from their bodies in order to maintain a homeostatic water balance. Owing to a large surface to volume ratio, arthropods are particularly susceptible to desiccation and have evolved behavioural and physiological mechanisms to conserve water. In social insects, water balance is also affected by the interactions between nestmates and by the architecture of the nest. For honeybees, humidity is particularly important for the brood because it affects the hatching success of eggs and because, unlike ants, honeybees cannot relocate their brood to parts of the nest with more favourable humidity. To advance the understanding of the water economy in honeybee nests, we investigated whether workers exhibit a hygropreference when exposed to a gradient of 24-90% relative humidity (RH) and whether the expression of this preference and their behaviour is affected by the presence of brood. The results show that young honeybee workers in the absence of brood exhibit a weak hygropreference for approximately 75% RH. When brood is present the expression of this preference is further weakened, suggesting that workers tend to the brood by distributing evenly in the gradient. In addition, fanning behaviour is shown to be triggered by an increase in humidity above the preferred level but not by a decrease. Our results suggest that humidity in honeybee colonies is actively controlled by workers.     

意大利工蜂前胃显微结构观察

通过解剖镜和扫描电子显微镜对意大利工蜂Apismellifera ligusticaL.前胃的形态结构进行了观察,发现前胃包括前胃瓣和前胃管两部分。前胃瓣是由4个瓣片环围而成,球形,在蜜囊中,每个瓣片的长度约为0.8mm,前端为三角形结构,可以运动,边长约为0.35mm,三角形的前缘有较长的毛形结构。在每个三角形顶端各有一个直径约为50μm瘤形突起。前胃瓣最大孔径为0.89～1.00mm,具有调整和控制食物进入中肠的功能。前胃管是一直径0.01～0.02mm的较为柔软的管道,插入中肠5mm,该结构可防止中肠食物的倒流。前胃瓣上有7种毛状结构,分布在前胃瓣的不同部位,该结构的功能是分离和过滤、捕捉和感觉功能。本研究为理解工蜂前胃在消化系统中的功能和作用以及昆虫形态学和昆虫分类学提供理论依据。     

Simultaneous and successive colour discrimination in the honeybee (Apis mellifera)

The colour discrimination of individual free-flying honeybees (Apis mellifera) was tested with simultaneous and successive viewing conditions for a variety of broadband reflectance stimuli. For simultaneous viewing bees used form vision to discriminate patterned target stimuli from homogeneous coloured distractor stimuli, and for successive discrimination bees were required to discriminate between homogeneously coloured stimuli. Bees were significantly better at a simultaneous discrimination task, and we suggest this is explained by the inefficiency with which the bees brain can code and retrieve colour information from memory when viewing stimuli successively. Using simultaneous viewing conditions bees discriminated between the test stimuli at a level equivalent to 1 just-noticeable-difference for human colour vision. Discrimination of colours by bees with simultaneous viewing conditions exceeded previous estimates of what is possible considering models of photoreceptor noise measured in bees, which suggests spatial and/or temporal summation of colour signals for fine discrimination tasks. The results show that when behavioural experiments are used to collect data about the mechanisms facilitating colour discrimination in animals, it is important to consider the effects of the stimulus viewing conditions on results.     

Morphological alterations induced by boric acid and fipronil in the midgut of worker honeybee (<Emphasis Type=Italic>Apis mellifera L.</Emphasis>) larvae

Morphological alterations, by means of histological and ultrastructural analysis, have been used to determine the effects of boric acid and fipronil on midgut tissues of honeybee worker, Apis mellifera L. larvae. In order to observe possible morphological alterations in the midgut, two groups of bioassays were performed. In the first one, the larvae were chronically treated with different concentrations of boric acid added to the food (1.0, 2.5 and 7.5 mg/g). In the second group, the larvae were fed with diets containing different concentrations of fipronil (0.1 and 1 μg/g) and compared with control groups without these chemical compounds. In the first bioassay, the larvae were collected on day 3 and in the second bioassay on day 4, when the mortality rate obtained in the toxicological bioassay was not very high. The larval midguts were removed and processed for morphological analyses using a light and transmission electron microscopy. We observed cytoplasmic vacuolizations, with the absence of autophagic vacuoles, and chromatinic compacting in most of the cells in the groups treated with pesticides. The morphological alterations were far greater in the larvae treated with boric acid than in the larvae treated with fipronil. Our data suggest that the midgut cell death observed was in response to boric acid and fipronil action. This study significantly improves the understanding of the toxicological effect of these insecticides from the ecotoxicological perspective.     

Light and electron microscopical observations on sperm cells of Guizotia abyssinica (Asteraceae)

The sperm cells of Guizotia abyssinica were studied during pollen development by light microscopy and at anther dehiscence by transmission electron microscopy. During development, the nuclei change shape from spherical to elongate, thread-like and banded. They are straight or folded, and rarely spiral-shaped when present in the pollen tube. Electron microscopy disclosed that the elongated sperm nuclei are apparently lobate. Intermittently, they are constricted and attenuated or convoluted. The major part of the sperm chromatin is condensed and peripheral, while a minor part is dispersed and central. The scanty sperm cytoplasm contains mitochondria and starch granules. The cytoplasm is mainly restricted to spaces adjoining constricted, lobed and convoluting nuclear sites. Some cytoplasmic patches become embayed in the nucleus at these sites. The periplasm bordering the sperm cells may originate from lucid dilations of the lumen between the plasma membranes of the sperm and vegetative cells. The periplasm is sometimes partially or entirely surrounded by double-membraned endoplasmic reticulum. Folded sperm cells with less coherent periplasm possibly represent a late stage preceding discharge into the pollen tube. The sperm cells always precede the vegetative nucleus into the pollen tube.     

Pheromonal dominance and the selection of a socially parasitic honeybee worker lineage (Apis mellifera capensis Esch.)

The recent invasion by self-replicating socially parasitic Cape honeybee workers, Apis mellifera capensis, of colonies of the neighbouring African subspecies Apis mellifera scutellata represents an opportunity to study evolution of intraspecific parasitism in real time. As honeybee workers compete pheromonally for reproductive dominance, and as A. m. capensis workers readily produce queen-like pheromones, we hypothesized that these semiochemicals promoted the evolution of intraspecific social parasitism. Remarkably, the offspring of a single worker became established as a parasite in A. m. scutellata's range. This could have resulted from extreme selection among different clonal parasitic worker lineages. Using pheromonal contest experiments, we show that the selected parasitic lineage dominates in the production of mandibular gland pheromones over all other competitors to which it is exposed. Our results suggest that mandibular gland pheromones played a key role in the evolution of intraspecific social parasitism in the honeybee and in the selection of a single genotype of parasitic workers.     

Life expectancy and onset of foraging in the honeybee (Apis mellifera)

Predictions that precocious foraging in honeybee workers is a result of shortening of their life expectancy were tested in both laboratory and field experiments. In the laboratory experiment, we assessed the impact of anaesthesia with CO₂ and infection with Nosema apis on the lifespan of workers. In the field experiment, the age at onset of foraging was observed in groups of workers with different expected lifespans. In both the experiments, workers originating from one queen inseminated with the semen of one drone were divided into five groups. The first group was anaesthetized with CO₂ on the first day of life. Workers from the other three groups were individually inoculated with a constant number of N. apis spores on the 1st, 6th and 11th days of life. Workers from the fifth control group were neither treated with CO₂ nor inoculated in any way. Both the laboratory and field experiments revealed that anaesthetized and infected workers had shorter expected lifespans compared to control bees. Amongst infected workers, those inoculated earlier in life survived for a significantly shorter period of time in comparison to those infected later in life. In agreement with the expectation, the field experiment showed that anaesthetized and infected workers with shorter expected lifespan start foraging earlier than control workers. Amongst the infected workers, age at inoculation correlated with age at onset of foraging. This means that short-lived workers complete safe nest tasks and begin riskier foraging earlier in life. Our results provide a strong support for the hypothesis that the division of labour in eusocial insects is a consequence of the different expected worker lifespan and different risk associated with their tasks; however, they do not contradict other existing explanations.     

Scanning electron microscope observations on the pathological changes of Malpighian tubules in the worker honeybee,Apis mellifera,infected by Malpighamoeba mellificae

A mixed population of cysts, immature cysts, and trophozoites was observed in the lumen of Malpighian tubules of Apis mellifera infected with Malpighamoeba mellificae. The most distinct pathological change in the infected tubules was swelling of the brush border of epithelial cells. In some areas the brush border was broken down into pieces, and in some cases it was completely engulfed by the parasites. The microvilli of the brush border were long and slender in noninfected tubules. Nuclei were not found in the infected tubules, but were frequently observed in the non-infected tubules. Numerous secretion globules were observed in the cytoplasm of epithelial cells of noninfected Malpighian tubules, but not in the cells of infected tubules. Epithelial cells in the infected tubules were destroyed and consumed by the trophozoites of M. mellificae. Trophozoites possessed protrusions and pits on their surfaces; many also had pseudopodia and apparently consumed the host cell by a mechanism of phagocytosis or endocytosis.     

Cuticular sclerotization in the honeybee (Apis mellifera adansonii)

Summary A micromethod has been developed for quantitative determinations of ketocatechols released by acid hydrolysis from samples of sclerotized insect cuticle, weighing from 0.1 to 5 mg. The method has been used to follow the changes in yield of ketocatechols from five different types of cuticle during honeybee development. Samples from workers, drones, and queens have been analyzed. The increase in yield of ketocatechols is most pronounced during the period of pharate development when abdominal cuticle is stiffened and the cuticular proteins become insoluble.     

Early developmental processes in the fertilised honeybee (Apis mellifera) oocyte

The behaviour of sperm from egg penetration until creation of the zygote, the development of the maternal pronucleus, and the two first cleavage divisions were studied by use of fluorescence microscopy. It was found that 4-12 sperm penetrate the egg membranes prior to oviposition. Contrary to previous reports, we found that only 1-7 sperm move from their initial location just beneath the vitelline membrane and into the cytoplasm, where they develop into paternal pronuclei. At the time of oviposition, the oocyte nucleus was usually at the stage of metaphase I, rather than anaphase I as previously reported. At 26+/-2.5 minutes the meiotic process had entered the stage of metaphase II. The paternal and maternal pronuclei formed at 55+/-2.6 minutes, and they fused at 93+/-7.3 minutes. The mitotic division of the zygote was completed at 119+/-6.5 minutes.     

Second-order ocellar neurons in the brain of the honeybee (Apis mellifera)

Summary Electrophoretic injection of Procion Yellow M-R4 into the ocellar tract of the worker bee has revealed the following:Two types of giant axon run from the lateral ocellus to the circumesophageal neuropile, where one branches ipsilaterally and the other contralaterally. A third type comes from the median ocellus and can be traced into the cervical connectives. The largest dendritic complex is in the circumesophageal neuropile; in addition, fiber endings have been demonstrated in the following areas: in the subretinal region, along the optic commissure, in the medulla interna, in the subesophageal ganglion and between the neurosecretory cells of the pars intercerebralis. — The giant fibers are enclosed in a glial sheath.Three types of cell body are described. One is associated with the glia; another, larger cell type comprises giant-axon somata. The third type of cell is small, and cannot yet be identified.Some of the histological results are discussed with respect to the possible function of the ocellus.     

Pattern discrimination by the honeybee (Apis mellifera): training on two pairs of patterns alternately

Pattern discrimination in the honeybee was studied by training alternately with two different pairs of patterns. Individually marked bees made a forced choice from a fixed distance in a standard Y-choice maze for a reward of sugar solution. Bees were trained, first on one pair of patterns for 10min then on a second pair, and so on, alternately between the two pairs. The pairs of patterns were selected to test the hypothesis that bees have a limited number of parallel mechanisms for the detection and discrimination of certain generalized global features. If this is so, it might be expected that each channel could process one pair of patterns simultaneously, but two pairs of patterns that are processed by the same channel would interfere with each other during the learning process. Features tested were: average orientation of edges, radial and tangential edges based on a symmetry of three or six, the position of a black spot, and the exchange of black and white. The bees fail to learn when the two alternated pairs of patterns offer the same feature, and they discriminate when the pairs offer two different features.