Adult Bees Research Articles

Impact of nutritional stress on the honeybee colony health

Honeybees Apis mellifera are important pollinators of wild plants and commercial crops. For more than a decade, high percentages of honeybee colony losses have been reported worldwide. Nutritional stress due to habitat depletion, infection by different pests and pathogens and pesticide exposure has been proposed as the major causes. In this study we analyzed how nutritional stress affects colony strength and health. Two groups of colonies were set in a Eucalyptus grandis plantation at the beginning of the flowering period (autumn), replicating a natural scenario with a nutritionally poor food source. While both groups of colonies had access to the pollen available in this plantation, one was supplemented with a polyfloral pollen patty during the entire flowering period. In the short-term, colonies under nutritional stress (which consumed mainly E. grandis pollen) showed higher infection level with Nosema spp. and lower brood and adult bee population, compared to supplemented colonies. On the other hand, these supplemented colonies showed higher infection level with RNA viruses although infection levels were low compared to countries were viral infections have negative impacts. Nutritional stress also had long-term colony effects, because bee population did not recover in spring, as in supplemented colonies did. In conclusion, nutritional stress and Nosema spp. infection had a severe impact on colony strength with consequences in both short and long-term.

Host-parasitoid interactions between the solitary bee Centris analis (Apidae: Centridini) and conopid flies (Diptera: Conopidae).

Natural enemies are one of the main mortality factors in bees and wasps attacking either immature stages or adults of their hosts. Dipterans of the genus Physocephala (Diptera: Conopidae) are parasitoids that attack adult bees during their field activities, and the parasitoid larvae develop inside the host abdomen. However, little is known about the biology of these natural enemies and their interactions with their solitary bee hosts. This study is aimed at analyzing attacks by conopid flies in one of their hosts, the solitary bee species Centris analis (Apidae: Centridini), and the consequences in the nesting behavior of this bee species. Higher incidences of parasitism occurred during the hot/wet season, and seven fly species attacking C. analis were identified. Of the fifty-six females observed during their nesting activities, seven of them were parasitized. These females showed alterations in their nesting behavior, depositing extra oil on the plug of finished nests and building plugs in empty cavities. The behavioral changes observed in these females began during larval stage L1 of the parasitoid. In the last stages of parasitoid development (L3 PUP and pupa), the bees ceased their flight activities and entered cavities at the nesting site, remaining there until death.

Organic farming positively affects honeybee colonies in a flower‐poor period in agricultural landscapes

Abstract Conventional farming has been implicated in global biodiversity and pollinator declines and organic farming is often regarded as a more ecological alternative. However, the effects of organic farming on honeybees remain elusive, despite honeybees’ importance as pollinators of crops and wild plants. Using 6 years of data from a large‐scale study with fortnightly measurements of honeybee colony performance traits (10 apiaries per year distributed across a 435 km2‐large research site in France), we related worker brood area, number of adult bees and honey reserves to the proportions of organic farmland in the surroundings of the hives at two spatial scales (300 m and 1,500 m). We found evidence that, at the local scale, organic farming increased both worker brood production and number of adult bees in the period of flower scarcity between the blooms of oilseed rape and sunflower (hereafter ‘dearth period’). At the landscape scale, organic farming increased honey reserves during the dearth period and at the beginning of the sunflower bloom. The results suggest that worker brood development benefitted from organic farming mostly through a more diverse diet due to an increase in the availability of diverse pollen sources in close proximity of their hives. Reduced pesticide drift may have additionally improved bee survival. Honey reserves were possibly mostly affected by increased availability of melliferous flowers in foraging distance. Synthesis and applications. Organic farming increases honeybee colony performance in a period of resource scarcity, likely through a continuous supply of floral resources including weeds, cover crops and semi‐natural elements. We demonstrate how worker brood area increases in the critical dearth period (between the blooms of oilseed rape and sunflower). This has previously been linked to winter colony survival, suggesting that organic farmland may mitigate repercussions of intensive farming on colony vitality. We conclude that organic farming benefits a crucial crop pollinator with potential positive implications for agriculture in the wider landscape.

Comparative morphology of adult honey bees, Apis mellifera, reared in vitro or by their parental colony

The environment in which an individual western honey bee (Apis mellifera) develops can have a major effect on its body condition and size. Artificial rearing of honey bee larvae is a popular tool used to assess the risks that numerous potential stressors, including pesticides and pathogens, pose to developing honey bees. We conducted a study comparing the morphologies and dry body weights of adult workers that were reared in vitro with those reared in a hive. There was no statistically detectable effect of rearing environment on hind wing length, head width, or basitarsus length, but there were detectable effects on forewing length and width, dry body weight, and hypopharyngeal gland size. Morphometric data are a valuable first step in comparisons, but they should be considered in conjunction with other biologically relevant assays as changes in morphology due to rearing environment do not guarantee changes in behavior.

The levels of natural Nosema spp. infection in Apis mellifera iberiensis brood stages

Nosema ceranae is the most prevalent endoparasite of Apis mellifera iberiensis and it is a major health problem for bees worldwide. The infective capacity of N. ceranae has been demonstrated experimentally in honey bee brood, however no data are available about its prevalence in brood under natural conditions. Thus, brood combs from 10 different hives were analyzed over two consecutive years, taking samples before and after winter. A total of 1433 larvae/pupae were analyzed individually and N. ceranae (3.53%) was the microsporidian most frequently detected, as opposed to Nosema apis (0.42%) which was more frequently detected in conjunction with N. ceranae (0.71%). The active multiplication of both microsporidians was confirmed by the expression (real-time-PCR) of the N. ceranae polar tube protein 3 gene and/or the N. apis RNA polymerase II gene in 24% of the brood samples positive for Nosema spp. Both genes are related to microsporidian multiplication. As such, N. ceranae multiplication was confirmed in 1.06% of the samples, while N. apis multiplication was only observed in co-infections with N. ceranae (0.07%). Brood cells were analyzed for the presence of Nosema spp., as those are the immediate environment where the brood stages develop. The brood samples infected by Nosema spp. were in brood cells in which that microsporidians were not detected, while brood cells positive for N. ceranae hosted brood stages that were not apparently infected, indicating that this is unlikely to be the main pathway of infection. Finally, the colonies with brood infected by N. ceranae showed higher levels (numbers) of infected adult bees, although the differences were not significant before (P = 0.260), during (P = 0.055) or after (P = 0.056) brood sampling. These results show that N. ceranae is a bee parasite ubiquitous to all members of the colony, irrespective of the age of the bee. It is also of veterinary interest and should be considered when studying the epidemiology of the disease.

THE HAEMOCYTES EFFECT OF THE PAENIBACILLUS LARVAE SPORES IN ADULT HONEY BEE WORKERS ( APIS MELLIFERA L.)

This work aimed to study the pathogenic effect of the Paenibacillus larvae spores on adult honey bee workers to explain the death many of them in the communities affected by American foul brood disease. This work was done through two methods; first injected the microbial suspension in the intersegmental membrane of the back lymph cavity of adult bee workers. The blood films were done after 1, 2, 4&12 hrs. beginning of the injection method, while with the feeding method it carried out after one, two and three months. During the first period of the microbial injection one hour later an elongation and minor abnormalities were occurred in some blood cells. The second stage began after 2 hrs. is characterized by loss of the blood cells dye strength. After 4 hrs. the third stage is characterized by increase atrophies of some blood cells. The fourth and final stage after 24 hrs. abnormalities in most blood cells with sharp decline in their numbers clearly. This stage considers beginning end of the blood cells alive and the rapid death of most of bee workers was detected. This experiment affirms that adult bee workers can be affected by the Paenibacillus larvae spores. That may be one reason of death bee workers in infected bee colonies by the American foul brood disease.

Comparison of qPCR and Morphological Methods For Detection of Acarapis Woodi in Honey Bee Samples

Abstract The honey bee tracheal mite Acarapis woodi is an internal obligate parasite of adult honey bees (Apis mellifera). The small size of the mites and location within the bee’s trachea create a challenge for diagnostic identification. Detailed assessment of low-level mite infestation involves microscopic examination of the bee’s tracheae, but this traditional diagnostic method takes a long time. In recent years, new molecular diagnostic techniques have been developed to identify A. woodi with the use of PCRs. The purpose of this study was to compare the diagnostic sensitivity of microscopic examination and qPCR method for the detection of A. woodi in honey bee samples. Thirty-six samples were analyzed with both methods and qPCR was more sensitive than the microscopic method to detect A. woodi. This work demonstrates the practical application of molecular technology as a support tool for surveys and contingency management and to provide robust surveillance data on the presence or absence of A. woodi in honey bee colonies.

Selection for barriers between honey bees and a devastating parasite.

Rivaling pesticides and a dearth of flowers, the parasitic mite Varroa destructor presents a tremendous threat to western honey bees, Apis mellifera. A longstanding, but minor, pest for the Asian honey bee Apis cerana, these obligate bee parasites feast on developing and adult A.mellifera across several continents. Varroa reproduction is limited to a short window when developing bee pupae are concealed in wax cells. Mated females target developing bees just before pupation and then have about one day to initiate reproduction, eventually laying one male and up to several female offspring. Female mites often fail to reproduce at all, instead waiting in cells until their bee host finishes development and then hitching dangerous rides on a succession of adult bees for up to several weeks, before scouting for a new host pupa. In this issue of Molecular Ecology, Conlon et al. (2019) have explored mite reproductive success via a clever and thought-provoking association study. In so doing, they have identified a protein whose actions could be integral to the dance between bees and their mite parasites.

First molecular detection of Nosema ceranae in Azerbaijan

Nosemosis is an important adult honey bee disease and causes economic losses worldwide. The aim of this study was to determine the Nosema species in honey bees (Apis mellifera) of Azerbaijan. For this aim, honey bee samples were collected from the Central (Ganja), Northern (Qakh) and Southern (Astara) parts of the country. Samples were examined microscopically, and 10 out of 24 samples (41.6%) were found to be positive for Nosema sp. spores. Positive samples were tested with a multiplex-PCR for the detection of Nosema species. As a result of our study, we could not detect N. apis but we determined the N. ceranae for the first time in Azerbaijan.

A scientific note on the effect of oxalic acid on honey bee larvae

The approval of oxalic acid as a treatment for Varroa destructor infestation of honey bee hives gives beekeepers an additional option for controlling this devastating parasite and disease vector, but the effects of oxalic acid on developing bees are not completely understood. In this study, we find that doses of oxalic acid not reported to be toxic to adult bees are toxic to larval bees. While it has been recommended that oxalic acid only be used during broodless periods because it does not penetrate cappings and is only effective in killing phoretic mites, it is tempting to use it at other times of the year because of the dearth of effective treatment options. Knowing whether oxalic acid is toxic to larvae and at what doses is important for beekeepers as they manage their colony population throughout the year.

Infection Outcomes are Robust to Thermal Variability in a Bumble Bee Host-Parasite System.

Climate change-related increases in thermal variability and rapid temperature shifts will affect organisms in multiple ways, including imposing physiological stress. Furthermore, the effects of temperature may alter the outcome of biotic interactions, such as those with pathogens and parasites. In the context of host-parasite interactions, the beneficial acclimation hypothesis posits that shifts away from acclimation or optimum performance temperatures will impose physiological stress on hosts and will affect their ability to resist parasite infection. We investigated the beneficial acclimation hypothesis in a bumble bee-trypanosome parasite system. Freshly emerged adult worker bumble bees, Bombus impatiens, were acclimated to 21, 26, or 29°C. They were subsequently experimentally exposed to the parasite, Crithidia bombi, and placed in a performance temperature that was the same as the acclimation temperature (constant) or one of the other temperatures (mismatched). Prevalence of parasite transmission was checked 4 and 6 days post-parasite exposure, and infection intensity in the gut was quantified at 8 days post-exposure. Parasite strain, host colony, and host size had significant effects on transmission prevalence and infection load. However, neither transmission nor infection intensity were significantly different between constant and mismatched thermal regimes. Furthermore, acclimation temperature, performance temperature, and the interaction of acclimation and performance temperatures had no significant effects on infection outcomes. These results, counter to predictions of the beneficial acclimation hypothesis, suggest that infection outcomes in this host-parasite system are robust to thermal variation within typically experienced ranges. This could be a consequence of adaptation to commonly experienced natural thermal regimes or a result of individual and colony level heterothermy in bumble bees. However, thermal variability may still have a detrimental effect on more sensitive stages or species, or when extreme climatic events push temperatures outside of the normally experienced range.

An Examination of Exposure Routes of Fluvalinate to Larval and Adult Honey Bees (Apis mellifera).

Fluvalinate has been extensively used in the United States to combat honey bee colony loss due to Varroa destructor mites. Our objectives were to investigate the extent of fluvalinate contamination in commercially available wax and to define exposure pathways to larval and adult honey bees. All the commercial wax tested contained elevated fluvalinate concentrations, indicating a need for regulation of the sources of wax being rendered for resale. Based on the negative logarithm of the partition coefficient between wax and pollen (-0.54), it is evident that fluvalinate has the potential to actively transfer from the contaminated wax into hive matrices. This was confirmed by adding fluvalinate-dosed wax, fluvalinate-impregnated strips, or a combination of the 2 to hives. Larvae and adult bees were checked for fluvalinate exposure using gas chromatography-mass spectrometry analysis. Larvae had detectable concentrations of fluvalinate in all treatments. Bioaccumulation in adult bees was significantly affected by the interaction between treatment type and application time. In other words, residues from hives that only had fluvalinate-dosed wax were comparable to residues in hives that were actively being treated, suggesting that transfer of fluvalinate from wax into adult bees was an important exposure route. In conclusion, exposure of fluvalinate from contaminated wax and treatment strips to honey bees needs to be considered when the risk for colony loss in hives is being evaluated. Environ Toxicol Chem 2019;38:1356-1363. © 2019 SETAC.

Netted crop covers reduce honeybee foraging activity and colony strength in a mass flowering crop.

The widespread use of protective covers in horticulture represents a novel landscape‐level change, presenting the challenges for crop pollination. Honeybees (Apis mellifera L) are pollinators of many crops, but their behavior can be affected by conditions under covers. To determine how netting crop covers can affect honeybee foraging dynamics, colony health, and pollination services, we assessed the performance of 52 nucleus honeybee colonies in five covered and six uncovered kiwifruit orchards. Colony strength was estimated pre‐ and postintroduction, and the foraging of individual bees (including pollen, nectar, and naïve foragers) was monitored in a subset of the hives fitted with RFID readers. Simultaneously, we evaluated pollination effectiveness by measuring flower visitation rates and the number of seeds produced after single honeybee visits. Honeybee colonies under cover exhibited both an acute loss of foragers and changes in the behavior of successful foragers. Under cover, bees were roughly three times less likely to return after their first trip outside the hive. Consequently, the number of adult bees in hives declined at a faster rate in these orchards, with colonies losing on average 1,057 ± 274 of their bees in under two weeks. Bees that did forage under cover completed fewer trips provisioning their colony, failing to reenter after a few short‐duration trips. These effects are likely to have implications for colony health and productivity. We also found that bee density (bees/thousand flowers) and visitation rates to flowers were lower under cover; however, we did not detect a resultant change in pollination. Our findings highlight the need for environment‐specific management techniques for pollinators. Improving honeybee orientation under covers and increasing our understanding of the effects of covers on bee nutrition and brood rearing should be primary objectives for maintaining colonies and potentially improving pollination in these systems.

Impact of Varroa destructor and deformed wing virus on emergence, cellular immunity, wing integrity and survivorship of Africanized honey bees in Mexico.

The ectoparasitic mite Varroa destructor is the primary health problem of honey bees (Apis mellifera) worldwide. Africanized honey bees in Brazil have demonstrated tolerance to the mite, but there is controversy about the degree of mite tolerance of Africanized bees in other countries. This study was conducted to quantify the effect of V. destructor parasitism on emergence, hemocyte concentration, wing integrity and longevity of Africanized honey bees in Mexico. Africanized bee brood were artificially infested with V. destructor mites and held in an incubator until emergence as adults and compared to non-infested controls. Deformed wing virus (DWV) presence was determined in the mites used to infest the bees. After emergence, the bees were maintained in an incubator to determine survivorship. The percentage of worker bees that emerged from parasitized cells (69%) was significantly lower than that of bees emerged from non-infested cells (96%). Newly-emerged parasitized bees had a significantly lower concentration of hemocytes in the hemolymph than non-parasitized bees. Additionally, the proportion of bees with deformed wings that emerged from V. destructor-parasitized cells was significantly higher (54%) than that of the control group (0%). The mean survival time of bees that emerged from infested and non-infested cells was 8.5 ± 0.3 and 14.4 ± 0.4 days, respectively, and the difference was significant. We conclude that V. destructor parasitism and DWV infections kill, cause deformities and inhibit cellular immunity in developing Africanized honey bees, and significantly reduce the lifespan of adult bees in Mexico. These results suggest that the tolerance of Africanized bees to V. destructor is related to adult bee mechanisms.

Disentangling host-parasite-pathogen interactions in a varroa-resistant honeybee population reveals virus tolerance as an independent, naturally adapted survival mechanism

The ectoparasitic mite, Varroa destructor, is unarguably the leading cause of honeybee (Apis mellifera) mortality worldwide through its role as a vector for lethal viruses, in particular, strains of the Deformed wing virus (DWV) and Acute bee paralysis virus (ABPV) complexes. This multi-level system of host-parasite-pathogen interactions makes it difficult to investigate effects of either the mite or the virus on natural host survival. The aim of this study was to remove confounding effects of varroa to examine the role of virus susceptibility in the enhanced survival of a naturally adapted Swedish mite-resistant (MR) honeybee population, relative to mite-susceptible (MS) honeybees. Caged adult bees and laboratory reared larvae, from varroa-free colonies, were inoculated with DWV and ABPV in a series of feeding infection experiments, while control groups received virus-free food. Virus infections were monitored using RT-qPCR assays in individuals sampled over a time course. In both adults and larvae the DWV and ABPV infection dynamics were nearly identical between MR and MS groups, but MS adults suffered significantly higher mortality than MR adults. Results suggest virus tolerance, rather than reduced susceptibility or virus resistance, is an important component of the natural survival of this honeybee population.

Sex‐specific differences in emergence patterns of solitary, cavity‐nesting bee, Megachile rotundata

Circadian rhythms play an important role in synchronizing biological processes. These rhythms are often influenced by semi‐predictable period cues, such as photoperiod or thermoperiod, often referred to as zeitgebers. The alfalfa leafcutting bee, Megachile rotundata, is a solitary, cavity‐nesting bee known to synchronize its emergence with thermoperiods as the dominant cue. Bees emerge as adults from brood cells. Brood cells are constructed by females with leaves and provisioned with pollen and nectar. One egg is laid in each brood cell, and a nest is composed of multiple brood cells in series in the cavity. Offspring go through all of juvenile development and metamorphosis in the cavity. It is unknown if certain variations in thermoperiod affects the timing of emergence. Because brood cells are built in series in the nest, adult offspring must emerge in a specific order to prevent bees placed at the back of the cavity from emerging before those in the front. If a bee in the back were to emerge first it would chew through its siblings' brood cells, potentially killing them, in order to exit the cavity. Thus, regulating emergence is important. On average, male M. rotundata are smaller than females, and often the brood cells at the front of cavities contain male offspring. Because of this, bee weight and sex are hypothesized to affect timing of emergence. To test this hypothesis, we disarticulated nests and placed individual brood cells in an apparatus that automatically records emergence time. We placed bees in various thermoperiods and recorded emergence time, sex, and dry weight of adult bees. It is well known that adult male offspring begin emerging days before females. In this study male offspring emerged earlier in the day than females which could be important for mating strategies. Understanding the roles sex and weight play in emergence and how these factors interact with different thermoperiods will help us to understand the maternal contribution to offspring development.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

An integrated management strategy to prevent outbreaks and eliminate infection pressure of American foulbrood disease in a commercial beekeeping operation

The bacterial disease American Foulbrood (AFB), caused by the Gram-positive bacterium Paenibacillus larvae, is considered the most contagious and destructive infectious disease affecting honeybees world-wide. The resilient nature of P. larvae bacterial spores presents a difficult problem for the control of AFB. Burning clinically symptomatic colonies is widely considered the only workable strategy to prevent further spread of the disease. Antibiotic use is banned in EU countries, and although used commonly in the U.S. and Canada, it only masks symptoms and does not prevent the further spread of the disease. Not surprisingly, there is an increased demand for chemical-free strategies to prevent and control of AFB. The aim of this study was to implement a management program with a long-term perspective to reduce infection pressure and eliminate AFB outbreaks. The study was conducted within a commercial beekeeping operation in central Sweden that has previously experienced reoccurring AFB outbreaks. For 5 years, P. larvae were cultured from adult bee samples taken in the fall. The following spring, any identified sub-clinically infected colonies were shaken onto new material and quarantined from the rest of the beekeeping operation. After the first year clinical symptoms were not again observed, and during the 5 years of the study the proportion of apiaries harbouring P. larvae spores decreased from 74% to 4%. A multinomial regression analysis also clearly demonstrated that the proportion of infected colonies with the highest levels of spore counts disproportionately declined so that by the end of the study the only remaining infected apiaries were in the lowest spore count category (the three higher spore count categories having been eradicated). These results demonstrate the importance of management practices on AFB disease epidemiology. Early detection of subclinical spore prevelance and quarantine management as presented here can provide an effective sustainable chemical-free preventive solution to reduce both the incidence of AFB outbreaks and continued transmission risk at a large-scale.

Exposure to sublethal concentrations of methoxyfenozide disrupts honey bee colony activity and thermoregulation.

Methoxyfenozide is an insect growth regulator (IGR) commonly used in agriculture to simultaneously control pests and preserve beneficial insect populations; however, its impact on honey bees in not fully understood. We conducted field and laboratory experiments to investigate bee health in response to field-relevant concentrations of this pesticide. Significant effects were observed in honey bee colony flight activity and thermoregulation after being exposed over 9 weeks to supplemental protein patty containing methoxyfenozide. Compared to bee colonies in the control group, colonies fed pollen patty with 200 ppb methoxyfenozide (as measured by residue analysis) had: 1) a significantly reduced rate of weight loss due to forager departure in the morning; and 2) higher temperature variability during the winter. Colonies in the 100 ppb (as measured by residue analysis) treatment group had values between the 200 ppb group and control for both response variables. The dusk break point, which is the time associated with the end of forager return, differed among all treatment groups but may have been confounded with direction the hives were facing. Bee colony metrics of adult bee mass and brood surface area, and measurements of bee head weight, newly-emerged bee weight, and hypopharyngeal gland size were not significantly affected by methoxyfenozide exposure, suggesting that there may be significant effects on honey bee colony behavior and health in the field that are difficult to detect using standard methods for assessing bee colonies and individuals. The second experiment was continued into the following spring, using the same treatment groups as in the fall. Fewer differences were observed among groups in the spring than the fall, possibly because of abundant spring forage and consequent reduced treatment patty consumption. Residue analyses showed that: 1) observed methoxyfenozide concentrations in treatment patty were about 18–60% lower than the calculated concentrations; 2) no residues were observed in wax in any treatment; and 3) methoxyfenozide was detected in bee bread only in the 200 ppb treatment group, at about 1–2.5% of the observed patty concentration.

Repellency of insecticides and the effect of thiacloprid on bumble bee colony development in red clover (Trifolium pratense L.) seed crops

ABSTRACTThe study intended to compare repellency of three insecticides on bumble bees and honey bees in Norwegian red clover (Trifolium pratense L.) seed crops, and to examine effects of thiacloprid on bumble bee colony development in the field. The repellency study was carried out in a large-scale field trial in SE Norway in 2013. On average for observations during the first week after spraying, 17 and 40% less honey bees (P = .03) and 26 and 20% less bumble bees (P = .36) were observed on plots sprayed with the pyrethroids lambda-cyhalothrin and alpha-cypermethrin, respectively, than on unsprayed control plots. No pollinator repellency was found on plots sprayed with the neonicotinoid thiacloprid. Compared with unsprayed control the seed yield increases were 22% on plots sprayed with thiacloprid vs. 12–13% on plots sprayed with pyrethroids (P = .10). Follow-up studies in 2014–2016 focused on the effect of thiacloprid on bumble bee colony development in commercially reared nests of Bombus terrestris placed into red clover seed crops at the start of flowering. Unsprayed control crops were compared with crops sprayed either at the bud stage or when 18–44% of flower heads were in full bloom. Chemical analyses of adult bumble bees showed that thiacloprid was taken up in bees when crops were sprayed during flowering, but not detected when crops were sprayed at the bud stage. The bumble bees in late-sprayed crops also developed weaker colonies than in unsprayed crops. Dead bees with a high internal concentration of thiacloprid were found in one crop sprayed during the night at 35% flowering. This shows that thiacloprid is not bee-safe if sprayed after anthesis and that spraying has to be conducted at the bud stage to reduce its contamination of nectar and pollen.

Ultramorphology of the peritrophic matrix in bees (Hymenoptera: Apidae)

The midgut is a region of the alimentary canal of bees with the lumen lined by a peritrophic matrix (PM) that is composed of chitin and proteins, secreted in response to feeding stimulus. The PM in adult bees has been described only under histological aspects. The objective of this work was to describe the PM in different bee species with a scanning electron microscope. The PMs have different features among the species analyzed. In the stingless bee Melipona quadrifasciata (Meliponini), the PM has two layers and the surface associated with the ectoperitrophic space has a hexagonal sculpture, whereas the endoperitrophic surface shows some wrinkles. In the honey bee Apis mellifera (Apini), and in the solitary bees Centris fuscata (Centridini) and Epicharis flava (Centridini) the PM has a laminate aspect with thin and irregular layers with dense material covering their surface, likely found for non Apidae bees Megachile rotundata (Megachilidae) and Oxaea flavescens (Andrenidae). These data suggest that the PM varies according to the bee species, which may be due to phylogeny other than feeding habits.