Hypopharyngeal Gland Development Research Articles

Changes in Vitellogenin, Abdominal Lipid Content, and Hypopharyngeal Gland Development in Honey Bees Fed Diets with Different Protein Sources.

Honey bees play an important role in the pollination of flowering plants. When honey bee colonies are deficient in pollen, one of their main nutrients, protein supplements are required. In this study, the effects of diets with six different protein sources on the physiological characteristics of worker bees (vitellogenin (Vg), abdominal lipid content (ALC), hypopharyngeal gland (HPG)) and consumption were investigated. The protein sources of the diets (diet I, …, diet VI) included pollen, spirulina dust (Arthrospira platensis Gomont), fresh egg yolk, lyophilized lactose-free skimmed milk powder, active fresh yeast, and ApiProtein. It was identified that consumption by worker bees was highest in the diet group supplemented with spirulina (diet II). Although there was no statistical difference regarding the Vg content in the hemolymph, numerically, the highest content was found in diet group IV (lyophilized lactose-free skimmed milk powder) (4.73 ± 0.03 ng/mL). ALC and HPG were highest in the group fed diet II. These results suggest that offering honey bees diets with certain protein sources can support their physiological traits.

Consumption of Citric Acid by Bees Promotes the Gland Development and Enhances Royal Jelly Quality.

The glands of bees are responsible for generating and secreting various biologically active substances that significantly impact bee physiological health and adaptability. This study aimed to investigate the effects of adding citric acid (CA) to bee feed on gland development and royal jelly quality. By formulating feed with varying proportions of CA, evaluation was undertaken of pollen feeding by honeybees under laboratory conditions, along with the impact of CA on the development of major glands, to determine suitable addition proportions. Further optimization of the CA proportion involved feeding colonies and evaluating royal jelly production and quality. The results indicated that feed containing 0.75% CA significantly extended the lifespan of bees and increased their pollen consumption. Gland development in bees showed a positive correlation with CA addition within the range of 0.25% to 0.75%, especially at 0.50% and 0.75%, which notably accelerated the development of mandibular, hypopharyngeal, and cephalic salivary glands, with active proliferation and differentiation of glandular cells and maintenance of normal gland size and morphology. CA added to feed stimulated vigorous secretion of wax glands in worker bees, resulting in prolific wax construction. Colonies consuming feed containing 0.50% CA produced royal jelly with significantly reduced moisture and total sugar content and increased levels of 10-HDA, total phenolic acids, total proteins, and acidity. These findings demonstrate that CA consumption significantly prolongs bee lifespan, increases consumption, promotes gland development, and enhances royal jelly quality. This research provides theoretical guidance for beekeeping practices and feed development, contributing to the sustainable advancement of apiculture.

Developmental exposure to hormone-mimicking insect growth disruptors alters expression of endocrine-related genes in worker honey bee (Hymenoptera: Apidae) brains and hypopharyngeal glands.

Division of labor within a honey bee colony creates a codependence between bees performing different tasks. The most obvious example of this is between the reproductive queen and worker bees. Queen bees lay 1,000 or more eggs a day, while young worker bees tend and feed queens. Young workers and queens can be exposed to pesticides when foragers return to the hive with contaminated resources. Previous research has found negative effects of larval exposure to insect-growth disruptors (IGD) methoxyfenozide and pyriproxyfen, on adult responsiveness to artificial queen pheromone. The present work investigates potential physiological and molecular mechanisms underpinning this behavioral change by examining the development of hypopharyngeal glands and ovaries as well as the expression of genes related to reproduction and worker endocrine signaling in the brain and hypopharyngeal gland tissues. Though hypopharyngeal gland and ovary development were not altered by developmental exposure to IGDs, gene expression differed. Specifically, in the brain tissue, ilp1 was downregulated in bees exposed to pyriproxyfen during development, and Kr-h1 was downregulated in both methoxyfenozide- and pyriproxyfen-exposed bees. In the hypopharyngeal glands, Kr-h1, EcR-A, EcR-B, and E75 were upregulated in honey bees exposed to methoxyfenozide compared to those in the pyriproxyfen or control treatments. Here we discuss these results and their potential implications for the health and performance of honey bee colonies.

Effects of Sucrose Feeding on the Quality of Royal Jelly Produced by Honeybee Apis mellifera L.

Royal jelly (RJ) is a highly nutritious secretion of the honeybees' hypopharyngeal glands (HPGs). During RJ production, colonies are occasionally subjected to manual interventions, such as sucrose feeding for energy supplementation. This study aimed to assess the impact of sucrose feeding on the composition of RJ. The results indicated that RJ obtained from sucrose-fed colonies exhibited significantly higher levels of fructose, alanine, glycine, tyrosine, valine, and isoleucine compared to the honey-fed group. However, no significant differences were observed in terms of moisture content, crude protein, 10-HDA, glucose, sucrose, minerals, or other amino acids within the RJ samples. Moreover, sucrose feeding did not have a significant effect on midgut sucrase activity, HPGs development, or the expression levels of MRJP1 and MRJP3 in nurse bees. Unsealed stored food samples from sucrose-fed bee colonies demonstrated significantly higher sucrose levels compared to sealed combs and natural honey. Additionally, natural honey exhibited higher moisture and Ca levels, as well as lower levels of Zn and Cu, in comparison to honey collected from bee colonies fed sucrose solutions. Based on these findings, we conclude that sucrose feeding has only a minor impact on the major components of RJ.

Influence of the food protein on the development of hypopharyngeal glands, fat body, quality and lifespan of honeybees

Research on the anatomical and physiological characteristics of bees (the state of fat body, hypopharyngeal glands) in connection with changes in natural and climatic conditions (soil composition, prolonged droughts, prolonged rains, cold weather, environmental disasters) impoverishment of fodder base for bees due to the decrease of sown areas of honey crops leading to the use of bees’ feeding, is relevant. The research aims to study the influence of food protein on the development of hypopharyngeal glands, fat body and life expectancy of honeybees. The zootechnical (the setting of the scientific research, the feeding of the bee families, the power of the bee families, productivity), ethological (orientation in the bee-entrance area), micrometrical (physiological and morphological characteristics of the parts of the bee’s body), microscopic (analysis of hypopharyngeal glands and fat body of bees) and statistical (biometric data processing) methods were used in the study. The significant difference in their degree of development depending on the carbohydrate or protein feeding was identified. After feeding sugar syrup to bees, signs of protein malnutrition and the state of development of hypopharyngeal glands corresponding to the І-ІІ degrees were noted. Alveoli of hypopharyngeal glands were reduced, and underdeveloped, with marked spaces, whereas after feeding protein food in the form of sugar syrup with bee pollen the bees had well-developed hypopharyngeal glands. The alveoli of the hypopharyngeal glands of the researched bees filled out, grew milky, with no space between them, and were able to produce larval food. Such a state of the glands’ development corresponds to the ІV degree of the development of hypopharyngeal glands. The research results indicate that the development of the fat body of bees happens at a young age when bees consume protein food the most. It has been proven that protein feeding of the bee colonies of experimental groups contributed to the better development of hypopharyngeal glands in both old and young bees, which resulted in better provision of food for larvae and more active development of the bee colonies. Protein feeding of bees in early spring under conditions of limited supply of protein food contributes to the production of larger larvae, which in turn contributes to the production of more complete bees

Influence of Probiotics Feed Supplementation on Hypopharyngeal Glands Morphometric Measurements of Honeybee Workers Apis mellifera L.

More scientific study and methods that are compatible with the honeybee-specific probiotic bacteria are needed in modern beekeeping to increase the productivity and well-being of honeybees. The goal of the current study set out to investigate the possible effects of probiotics previously isolated from the honeybee intestinal tract and soybean patties on nurse worker bee hypopharyngeal gland (HPG) development. The experimentation was carried out in four different treatment groups in which probiotics and soybean patties were provided in different proportions, with control colonies. Results showed that there was a significant increase in HPG morphometric parameters of bees in all experimental groups. Control nurse worker fed with sugar syrup for only 2weeks had the smallest HPG morphometric parameters. The highest HPG diameter 14.89 ± 0.097µm and surface area 0.065 ± 0.001µm2 were observed in the bees group fed with both probiotic and soya patty. Additionally, the same trend was observed in all morphometric parameters with the bees group fed with probiotic bacteria and soya patty. More royal jelly can be produced by larger HPGs than by smaller ones. Thus, the use of probiotics as a natural alternative tool boosted the development of Apis mellifera nurse workers' HPG that will positively affect the beekeepers' economy by providing a higher yield of royal jelly production. Overall, the study's findings show that probiotics are a useful feed supplement for honeybees.

Effects of Bee Pollen Derived from Acer mono Maxim. or Phellodendron amurense Rupr. on the Lipid Composition of Royal Jelly Secreted by Honeybees.

Royal jelly is a specific product secreted by honeybees, and has been sought after to maintain health because of its valuable bioactive substances, e.g., lipids and vitamins. The lipids in royal jelly come from the bee pollen consumed by honeybees, and different plant source of bee pollen affects the lipid composition of royal jelly. However, the effect of bee pollen consumption on the lipid composition of royal jelly remains unclear. Herein, we examined the influence of two factors on the lipid composition of royal jelly: first, two plant sources of bee pollen, i.e., Acer mono Maxim. (BP-Am) and Phellodendron amurense Rupr. (BP-Pa); secondly, different feeding times. Lipidomic analyses were conducted on the royal jelly produced by honeybees fed BP-Am or BP-Pa using ultra-high performance liquid chromatography (UPLC)-Q-Exactive Orbitrap mass spectrometry. The results showed that the phospholipid and fatty acid contents differed in royal jelly produced by honeybees fed BP-Am compared to those fed BP-Pa. There were also differences between timepoints, with many lipid compounds decreasing in abundance soon after single-pollen feeding began, slowly increasing over time, then decreasing again after 30 days of single-pollen feeding. The single bee pollen diet destroyed the nutritional balance of bee colonies and affected the development of hypopharyngeal and maxillary glands, resulting in differences in royal jelly quality. This study provides guidance for optimal selection of honeybee feed for the production of high-quality royal jelly.

Expression Profile of microRNAs during Development of the Hypopharyngeal Gland in Honey Bee, Apis mellifera.

The hypopharyngeal gland is an important organ for honey bees to secrete royal jelly, and its secretory activity varies with the age of workers. However, by now, the regulation mechanism of hypopharyngeal gland development is still unclear. Here, the expression profiles of miRNAs in the hypopharyngeal gland of newly emerged workers, nurses, and foragers were investigated via small RNA sequencing. From these three stages, 81 known miRNAs and 135 novel miRNAs have been identified. A total of 85 miRNAs showed expression differences between different development stages, and their target genes were predicted to range from 1 to more than 10. Many of the differentially expressed miRNAs and target genes are related to growth and development or apoptosis. Moreover, dual-luciferase-reporter assays verified that novel-miR-11 directly targets the 3'-untranslated regions of LOC410685 (inactive tyrosine-protein kinase 7) and LOC725318 (uncharacterized protein). These results suggested that miRNAs were widely involved in the developmental regulation of the hypopharyngeal gland in honey bees.

Effects of Pollen Deprivation in Groups of Tellian (Apis mellifera intermissa) and Saharan (Apis mellifera sahariensis) Honey Bees under Controlled Conditions.

Simple SummaryPollen is a key element in bee nutrition, containing proteins, vitamins and lipids that support the vital functions of bees. Nutritional stress affects bees from the larval to the adult stage, both at the individual and colony levels. To face this type of stress, the bees developed behavioral and physiological mechanisms to fight against it. Such type of response can vary depending on the breed and age of the bees. In this study under controlled conditions, we investigated the impact of a protein-free diet on physiological functions, including survival, hypopharyngeal gland development, hemolymph proteins and ovarian development of two local bees, Apis mellifera intermissa and Apis mellifera sahariensis.Worldwide, honey bees are increasingly faced with periods of pollen scarcity, which can lead to nutritional deficiencies, especially of proteins and amino acids. These are essential for the proper functioning of the single organism and the colony. To understand how bees react to protein deficiency, under controlled conditions, we studied the effect of pollen deficiency on the main physiological parameters in two subspecies endemic of Algeria, Apis mellifera intermissa and Apis mellifera sahariensis. Emerging workers of both subspecies were reared with two diets: one was pollen-fed, whereas the other pollen-deprived. Several physiological criteria were measured depending on the type of diet and subspecies: the survival of the bees, the amount of total protein in the hemolymph, hypopharyngeal glands development and the ovary development of workers. These last three parameters were assessed at three different ages (7, 14 and 21 days). At birth, sahariensis workers weighed more than intermissa. With the same protein diet, the average life expectancy of sahariensis was extended by 5.55 days compared to intermissa. Even if deprived of pollen, sahariensis lived longer than intermissa fed with pollen (p < 0.001). In the three age levels, the hypopharyngeal glands were more developed and less affected by pollen deficiency (p < 0.001) in sahariensis than in intermissa (p < 0.001). The total hemolymph protein was higher in intermissa than in sahariensis regardless of the diet, and was also higher in protein-fed than in deprived bees (p < 0.001). The ovaries developed more rapidly with a high proportion in intermissa than in sahariensis (p < 0.05) regardless of the diet, and was also higher in the bees fed with pollen than those deprived (p < 0.05). Pollen deficiency generates physiological alterations and modifications, the amplitude of which varied according to the subspecies of the bee studied.

Survival, Body Condition, and Immune System of Apis mellifera liguistica Fed Avocado, Maize, and Polyfloral Pollen Diet.

Nutritional stress is the major factor contributing to decline in the honey bee (Apis mellifera L.) populations given the high degree of dependence on floral resources, and due to the habitat loss. In this sense, monocultures of maize and avocado have great extensions in Mexico, but their impact on the physiology and morphology of A. mellifera is unknown. This research evaluated the effect of total protein content in monofloral (maize or avocado pollen diets) and polyfloral (using five types of pollen: Persea americana Mill., Zea mays L., Melampodium perfoliatum Cav., Drymaria villosa Cham Schltdl., and Lopezia racemosa Cav.) on their survival, body condition (controlled density, head mass, and development of hypopharyngeal glands; protein content in hemolymph), and immune response [lytic activity and activity of prophenoloxidase in the hemolymph (proPO)]. Corbicular pollen of P. americana had the highest protein content, followed by the corbicular pollen of Z. mays, M. perfoliatum, D. villosa, and L. racemosa. Polyfloral diet seems to be better for A. mellifera than the monofloral maize and avocado. Bees fed polyfloral pollen diet showed a high content of protein in the hemolymph in comparison with that fed maize or avocado pollen diets. Bees fed polyfloral and avocado pollen diet had the highest lytic activity but showed a decrease in proPO activity. In conclusion, polyfloral diets seem to be better for A. mellifera than the monofloral maize and avocado.

The Beneficial Effect of Pollen on Varroa Infested Bees Depends on Its Influence on Behavioral Maturation Genes.

Honey bees collect nectar and pollen to fulfill their nutritional demands. In particular, pollen can influence longevity, the development of hypopharyngeal glands, and immune-competence of bees. Pollen can also mitigate the deleterious effects caused by the parasitic mite Varroa destructor and related deformed wing virus (DWV) infections. It has been shown that V. destructor accelerates the physiological and behavioral maturation of honey bees by influencing the interaction between two core physiological factors, Vitellogenin and juvenile hormone. In this study, we test the hypothesis that the beneficial effects of pollen on Varroa-infested bees are related to the hormonal control underpinning behavioral maturation. By analyzing the expression of genes associated to behavioral maturation in pollen-fed mite-infested bees, we show that treatment with pollen increases the lifespan of mite-infested bees by reversing the faster maturation induced by the parasite at the gene expression level. As expected, from the different immune-competence of nurse and forager bees, the lifespan extension triggered by pollen is also correlated with a positive influence of antimicrobial peptide gene expression and DWV load, further reinforcing the beneficial effect of pollen. This study lay the groundwork for future analyses of the underlying evolutionary processes and applications to improve bee health.

Functional response of the hypopharyngeal glands to a social parasitism challenge in Southern African honey bee subspecies.

Hypopharyngeal gland (HPG) development in honey bee workers is primarily age-dependent and changes according to the tasks performed in the colony. HPG activity also depends on colony requirements and is flexible in relation to the need for feeding brood. Very little is known about HPG development in the honey bee subspecies found in Southern Africa. We examined HPG development in Apis mellifera scutellata and A. m. capensis, including A. m. scutellata colonies infested with an invasive parasitic clonal lineage of A. m. capensis known to manipulate food provisioning to the parasitic larvae by their A.m. scutellata hosts, under natural in-hive conditions in bees aged 0 to 14days using light microscopy. We found marked differences in acini size (berry-like clusters of secretory cells) and the age at which maximum HPG development occurred between the subspecies and in the presence of the parasite. In A. m. scutellata workers, acini reached maximum size at 6days. The acini of A. m. capensis workers were larger (up to double) than those of A. m. scutellata and reached maximum size at 8days, while the HPG acini in A. m. scutellata workers infested with A. m. capensis clones reached development sizes similar to those of A. m. capensis at day 10 and were 1.5 times larger than those of uninfested A. m. scutellata. This provides foundational insights into a functional response affecting the development of the HPG most likely associated with brood pheromone composition and how this is altered in the presence of a social parasite.

Age and Behavior-Dependent Differential miRNAs Expression in the Hypopharyngeal Glands of Honeybees (Apis mellifera L.).

Simple SummaryThe hypopharyngeal glands (HPGs) are a pair of aciniform glands that are located in the frontal area of the heads of worker bees (Apis mellifera L.) that exhibit age and behavior-dependent development. Little is known about whether/how miRNAs regulate the HPGs development. In this study, small RNA sequencing was employed to analyze the miRNA profiles of HPGs in newly-emerged bees (NEB), nurse bees (NB), and forager bees (FB). We found that there were a total of 31 known miRNAs differentially expressed among the three stages, which might have regulatory roles in the growth and development, protein synthesis, and carbohydrate and energy metabolism in the HPGs. Additionally, the downregulation of ame-miR-184-3p and ame-miR-252a-5p in nurse bees may be involved in royal jelly secretion, while the lower expression of ame-miR-11-3p and ame-miR-281-3p in forager bees are responsible for honey processing.This study aims to investigate the expression differences of miRNAs in the hypopharyngeal glands (HPGs) of honeybees at three developmental stages and to explore their regulation functions in the HPGs development. Small RNA sequencing was employed to analyze the miRNA profiles of HPGs in newly-emerged bees (NEB), nurse bees (NB), and forager bees (FB). Results showed that a total of 153 known miRNAs were found in the three stages, and ame-miR-276-3p, ame-miR-375-3p, ame-miR-14-3p, ame-miR-275-3p, and ame-miR-3477-5p were the top five most abundant ones. Furthermore, the expression of 11 miRNAs, 17 miRNAs, and 18 miRNAs were significantly different in NB vs. FB comparison, NB vs. NEB comparison, and in FB vs. NEB comparison, respectively, of which ame-miR-184-3p and ame-miR-252a-5p were downregulated in NB compared with that in both the FB and NEB, while ame-miR-11-3p, ame-miR-281-3p, and ame-miR-31a-5p had lower expression levels in FB compared with that in both the NB and NEB. Bioinformatic analysis showed that the potential target genes of the differentially expressed miRNAs (DEMs) were mainly enriched in several key signaling pathways, including mTOR signaling pathway, MAPK signaling pathway-fly, FoxO signaling pathway, Hippo signaling pathway-fly. Overall, our study characterized the miRNA profiles in the HPGs of honeybees at three different developmental stages and provided a basis for further study of the roles of miRNAs in HPGs development.

Eusocial insect declines: Insecticide impairs sperm and feeding glands in bumblebees

Insecticides are contributing to global insect declines, thereby creating demand to understand the mechanisms underlying reduced fitness. In the eusocial Hymenoptera, inclusive fitness depends on successful mating of male sexuals (drones) and efficient collaborative brood care by female workers. Therefore, sublethal insecticide effects on sperm and glands used in larval feeding (hypopharyngeal glands (HPG)) would provide key mechanisms for population declines in eusocial insects. However, while negative impacts for bumblebee colony fitness have been documented, the effects of insecticide exposure on individual physiology are less well understood. Here, we show that field-realistic concentrations (4.5–40 ng ml−1) of the neonicotinoid insecticide thiamethoxam significantly impair Bombus terrestris sperm and HPGs, thereby providing plausible mechanisms underlying bumblebee population decline. In the laboratory, drones and workers were exposed to five thiamethoxam concentrations (4.5 to 1000 ng ml−1). Then, survival, food consumption, body mass, HPG development, sperm quantity and viability were assessed. At all concentrations, drones were more exposed than workers due to higher food consumption. Increased body mass was observed in drones starting at 20 ng ml−1 and in workers at 100 ng ml−1. Furthermore, environmentally realistic concentrations (4.5–40 ng ml−1) did not significantly affect survival or consumption for either sex. However, thiamethoxam exposure significantly negatively affected both sperm viability and HPG development at all tested concentrations. Therefore, the results indicate a trade-off between survival and fitness components, possibly due to costly detoxification. Since sperm and HPG are corner stones of colony fitness, the data offer plausible mechanisms for bumblebee population declines. To adequately mitigate ongoing biodiversity declines for the eusocial insects, this study suggests it is essential to evaluate the impact of insecticides on fitness parameters of both sexuals and workers.

The Effect of An Alternative Diet Fermented by Bee Bread Microorganisms on Hypopharyngeal Glands Development and Acini Size of Honey Bee Workers, (Apis mellifera L.)

The hypopharyngeal glands of worker bees located in the head; consist of thousands of two-cell units that are composed of a secretory cell and a duct cell and that are arranged in sets of about 12 around a long collecting duct. The glands contribute to the production of the royal jelly fed to queens and larvae. They are highly sensitive to the quantity and quality of the food as pollen and pollen substitutes that the nurse bee consumes. The role of the worker honey bee Apis mellifera L. changes depending on age after eclosion (age polyethism): young workers (nurse bees) take care of their brood by synthesizing and secreting brood food (royal jelly), while older workers (foragers) forage for nectar and process it into honey. In our experiment, we tested how diets impact hypopharyngeal gland development and their acini size, where our diets compared were (bee bread diet; unfermented diet; fermented diet in a simulation method for nature; and sucrose syrup). Also, we mentioned understanding the role of these glands in hive health. For this study, we have examined the morphogenesis of the hypopharyngeal gland during different ages of workers honeybee Apis mellifera L. that fed on the different diets; we measured the size of glandular acini in a robust measure. These results obtained indicated that the hypopharyngeal gland development has flexibility and can depending on the condition of the colony as the pollen substitute diet we prepared in the periods of food shortage in nature. This described the hypothesis that feeding plays an important role in the development of HG according to diet nutritional values, ensuring the importance of the fermentation process for the better health of honey bees.

The Importance of Time and Place: Nutrient Composition and Utilization of Seasonal Pollens by European Honey Bees (Apis mellifera L.).

Simple SummaryHoney bees rely on pollen and nectar to provide nutrients to support their yearly colony cycle. Specifics of the cycle differ among geographic regions as do the species of flowering plants and the nutrients they provide. We examined responses of honey bees from two different queen lines fed pollens from locations that differed in floral species composition and yearly colony cycles. We detected differences between the queen lines in the amount of pollen they consumed and the size of their hypopharyngeal glands (HPG). There were also seasonal differences between the nutrient composition of pollens. Spring pollens collected from colonies in both locations had higher amino and fatty acid concentrations than fall pollens. There also were seasonal differences in responses to the pollens consumed by bees from both queen lines. Bees consumed more spring than fall pollen, but digested less of it so that bees consumed more protein from fall pollens. Though protein consumption was higher with fall pollen, HPG were larger in spring bees.Honey bee colonies have a yearly cycle that is supported nutritionally by the seasonal progression of flowering plants. In the spring, colonies grow by rearing brood, but in the fall, brood rearing declines in preparation for overwintering. Depending on where colonies are located, the yearly cycle can differ especially in overwintering activities. In temperate climates of Europe and North America, colonies reduce or end brood rearing in the fall while in warmer climates bees can rear brood and forage throughout the year. To test the hypothesis that nutrients available in seasonal pollens and honey bee responses to them can differ we analyzed pollen in the spring and fall collected by colonies in environments where brood rearing either stops in the fall (Iowa) or continues through the winter (Arizona). We fed both types of pollen to worker offspring of queens that emerged and open mated in each type of environment. We measured physiological responses to test if they differed depending on the location and season when the pollen was collected and the queen line of the workers that consumed it. Specifically, we measured pollen and protein consumption, gene expression levels (hex 70, hex 110, and vg) and hypopharyngeal gland (HPG) development. We found differences in macronutrient content and amino and fatty acids between spring and fall pollens from the same location and differences in nutrient content between locations during the same season. We also detected queen type and seasonal effects in HPG size and differences in gene expression between bees consuming spring vs. fall pollen with larger HPG and higher gene expression levels in those consuming spring pollen. The effects might have emerged from the seasonal differences in nutritional content of the pollens and genetic factors associated with the queen lines we used.

Pollen Source Affects Development and Behavioral Preferences in Honey Bees.

Simple SummaryPollinators adjust their foraging preference based on the pollen cues of foraging plants. Honey bees, for example, prefer to collect one type of pollen from plants that bloom at the same time. In northern China, apricot and pear trees are the two main foraging plants in the early spring. However, honey bees tend to collect pollen from apricot trees. It is interesting to understand what affects the foraging decision of honey bees regarding these two pollen types. In this study, we observed the foraging preference of Apis mellifera workers with respect to apricot and pear pollen under laboratory conditions. The effect of pollen on the development of the hypopharyngeal gland (HG) and ovary was measured. The number of visits made to apricot pollen was significantly higher than that to pear pollen. Furthermore, the response of the HG and ovary to these two pollens was different. The development of the HG was significantly affected by pollen diet treatments. However, there was no significant difference in the ovarian development of caged workers supplied with the two different pollen diets. Overall, honey bees showed a significant preference for apricot pollen over pear pollen. Compared with the ovary, the HG of honey bee workers may be more sensitive to pollen nutrition.With the availability of various plants in bloom simultaneously, honey bees prefer to collect some pollen types over others. To better understand pollen’s role as a reward for workers, we compared the digestibility and nutritional value of two pollen diets, namely, pear (Pyrus bretschneideri Rehd.) and apricot (Armeniaca sibirica L.). We investigated the visits, pollen consumption, and pollen extraction efficiency of caged Apis mellifera workers. Newly emerged workers were reared, and the effects of two pollen diets on their physiological status (the development of hypopharyngeal glands and ovaries) were compared. The choice-test experiments indicated a significant preference of A. mellifera workers for apricot pollen diets over pear pollen diets (number of bees landing, 29.5 ± 8.11 and 9.25 ± 5.10, p < 0.001 and pollen consumption, 0.052 ± 0.026 g/day and 0.033 ± 0.013 g/day, p < 0.05). Both pollen diets had comparable extraction efficiencies (67.63% for pear pollen and 67.73% for apricot pollen). Caged workers fed different pollen diets also exhibited similar ovarian development (p > 0.05). However, workers fed apricot pollen had significantly larger hypopharyngeal glands than those fed pear pollen (p < 0.001). Our results indicated that the benefits conferred to honey bees by different pollen diets may influence their foraging preference.

Novel Insight Into the Development and Function of Hypopharyngeal Glands in Honey Bees.

Hypopharyngeal glands (HGs) are the most important organ of hymenopterans which play critical roles for the insect physiology. In honey bees, HGs are paired structures located bilaterally in the head, in front of the brain between compound eyes. Each gland is composed of thousands of secretory units connecting to secretory duct in worker bees. To better understand the recent progress made in understanding the structure and function of these glands, we here review the ontogeny of HGs, and the factors affecting the morphology, physiology, and molecular basis of the functionality of the glands. We also review the morphogenesis of HGs in the pupal and adult stages, and the secretory role of the glands across the ages for the first time. Furthermore, recent transcriptome, proteome, and phosphoproteome analyses have elucidated the potential mechanisms driving the HGs development and functionality. This adds a comprehensive novel knowledge of the development and physiology of HGs in honey bees over time, which may be helpful for future research investigations.

Physiological Effects of Some Pollen Substitutes Diets on Caged Honey Bee Workers (Apis mellifera L.)

Nutritional value of four proteinaceous diets and their physiological effects on honey bee workers were evaluated under laboratory conditions. The tested diets were as follows: diet 1 – date (Phoenix dactylifera L.) syrup, skimmed milk powder and dried brewer's yeast, diet 2 – Fenugreek (Trigonella foenum-graecum L.), Turmeric (Curcuma longa L.) powders and dried brewer's yeast, diet 3 – chickpea (Cicer arietinum L.) flour, wheat germ and dried brewer's yeast and diet 4 - soybean meal, skimmed milk powder and dried brewer's yeast, beside a control group (bee bread). Caged Carniolan honey bee workers were used in the experiments. The consumption rate, workers longevity, development degree of hypopharyngeal glands (HPG), and weight of rectal contents were determined. The greatest consumption rate was recorded for the control group while the lowest one was recorded for diet 4. Feeding bees on diet 3 gave the longest longevity (LT50= 27.0 days) among the tested diets and as a second rank after bees in the control group (LT50 = 29.0 days) while diet 4 showed the lowest longevity (LT50 =20.5 days). The highest HPG development degree (3.78) was recorded for 9 days old bees in the control group, followed by diet 3 (3.24) while the lowest degree (2.14) was to diet 4. The weight of rectal contents of honey bee workers was 13.43, 16.03 and 16.12 mg/bee/3 days for diet 3, diet 1 and diet 2, respectively, suggesting the suitability of these diets to bees. In light of this study, diet 3 and 2 have the best physiological effects for bees with good nutritional values.

Seasonal variation of flavonoid content in bee bread: Potential impact on hypopharyngeal gland development in Apis mellifera honey bees

Bee bread is the main source of proteins necessary for the development of hypopharyngeal glands in nurse bees. However, the seasonal chemical composition and its effects on honey bee physiology are poorly understood. Thus, this study evaluated how the season and botanical origin of pollen influence the content of crude protein, ash, and total flavonoids, as well as the profile of flavonoids, in Africanized Apis mellifera bee bread. The influence of these factors on the number and area of hypopharyngeal gland acini of nurse bees raised with similar numbers of brood frames over the four seasons of the year were also evaluated. The botanical families found in bee bread and the total flavonoid content and their chemical profile varied markedly with the seasons of the year, with the highest total flavonoid content found in the summer. The percentage of crude protein and ash in bee bread, however, did not change with the seasons. The number and area of acini in the hypopharyngeal gland significantly decreased during autumn and winter. Based on our results, flavonoids rather than crude protein may play a role in hypopharyngeal gland development in honey bees. Further studies to test artificial diets supplemented with flavonoids can improve beekeeping strategies and contribute to colony maintenance in periods of food shortage.