High-resolution (mtDNA) melting analysis for simple and efficient characterization of Africanized honey bee Apis mellifera (Hymenoptera:Apidae)

Analysis of the mtDNA variation in Apis mellifera L. has allowed distinguishing subspecies and evolutionary lineages by means of different molecular methods; from RFLP, to PCR-RFLP and direct sequencing. Likewise, geometric morphometrics (GM) has been used to distinguish Africanized honey bees with a high degree of consistency with studies using molecular information. High-resolution fusion analysis (HRM) allows one to quickly identify sequence polymorphisms by comparing DNA melting curves in short amplicons generated by real-time PCR (qPCR). The objective of this work was to implement the HRM technique in the diagnosis of Africanization of colonies of A. mellifera from Argentina, using GM as a validation method. DNA was extracted from 60 A. mellifera colonies for mitotype identification. Samples were initially analyzed by HRM, through qPCRs of two regions (485 bp/385 bp) of the mitochondrial cytochrome b gene (cytb). This technique was then optimizing to amplify a smaller PCR product (207 bp) for the HRM diagnosis for the Africanization of colonies. Of the 60 colony samples analyzed, 41 were classified as colonies of European origin whereas 19 revealed African origin. All the samples classified by HRM were correctly validated by GM, demonstrating that this technique could be implemented for a rapid identification of African mitotypes in Apis mellifera samples.

Pathogens Detection in the Small Hive Beetle (Aethina tumida (Coleoptera: Nitidulidae))

Aethina tumida Murray is currently a worldwide emergent pest of Apis mellifera L. hives. Although the damaging effect on the colony stores and brood is well known, the possible role of these beetles as a disease carrier is not clear. This is the first report of DNA presence of the trypanosome honeybee parasite Lotmaria passim and Crithidia bombi, and the Apis mellifera filamentous virus (AmFV) in A. tumida. Further studies will be needed to determine if A. tumida is indeed a mechanical or biological vector of these pathogens.

Heat shock proteins in Varroa destructor exposed to heat stress and in-hive acaricides

Varroa destructor is one of the major pests that affect honeybees around the world. Chemical treatments are common to control varroosis, but mites possess biochemical adaptive mechanisms to resist these treatments, enabling them to survive. So far, no information is available regarding whether these pesticides can induce the expression of heat shock protein (Hsp) as a common protective mechanism against tissue damage. The aims of this study were to determine differences in heat shock tolerance between mites collected from brood combs and phoretic ones, and to examine patterns of protein expression of Hsp70 that occur in various populations of V. destructor after exposure to acaricides commonly employed in beekeeping, such as flumethrin, tau-fluvalinate and coumaphos. Curiously, mites obtained from brood cells were alive at 40 °C, unlike phoretic mites that reached 100% mortality, demonstrating differential thermo-tolerance. Heat treatment induced Hsp70 in mites 4 × more than in control mites and no differences in response were observed in phoretic versus cell-brood-obtained mites. Dose-response assays were carried out at increasing acaricide concentrations. Each population showed a different stress response to acaricides despite belonging to the same geographic region. In one of them, coumaphos acted as a hormetic stressor. Pyrethroids also induced Hsp70, but mite population seemed sensitive to this treatment. We concluded that Hsp70 could represent a robust biomarker for measuring exposure of V. destructor to thermal and chemical stress, depending on the acaricide class and interpopulation variability. This is relevant because it is the first time that stress response is analyzed in this biological model, providing new insight in host-parasite-xenobiotic interaction.

Lactobacillus kunkeei strains decreased the infection by honey bee pathogens Paenibacillus larvae and Nosema ceranae

Due to their social behaviour, honey bees can be infected by a wide range of pathogens including the microsporidia Nosema ceranae and the bacteria Paenibacillus larvae. The use of probiotics as food additives for the control or prevention of infectious diseases is a widely used approach to improve human and animal health. In this work, we generated a mixture of four Lactobacillus kunkeei strains isolated from the gut microbial community of bees, and evaluated its potential beneficial effect on larvae and adult bees. Its administration in controlled laboratory models was safe for larvae and bees; it did not affect the expression of immune-related genes and it was able to decrease the mortality associated to P. larvae infection in larvae and the counts of N. ceranae spores from adult honey bees. These promising results suggest that this beneficial microorganism's mixture may be an attractive strategy to improve bee health. Field studies are being carried out to evaluate its effect in naturally infected colonies.

Synergistic effect of surfactin from Bacillus subtilis C4 and Achyrocline satureioides extracts on the viability of Paenibacillus larvae

The aim of this work was to determine the in vitro effect of the mixture between the lipopeptide surfactin, synthesized by Bacillus subtilis C4 (strain isolated from honey) and the most active vegetal extract from Achyrocline satureioides, a traditional medicinal plant, on local strains of Paenibacillus larvae, the agent of American Foulbrood in honeybees. Five P. larvae strains isolated in Córdoba, Argentina, were phenotypically characterized. These and 12 other P. larvae strains from different regions of Argentina were analysed. The antimicrobial activities of the essential oil, hexane (HE) and benzene extracts from A. satureioides were assessed against P. larvae and the HE showed the highest anti-P. larvae activity. A combination of the biosurfactant surfactin, produced by B. subtilis C4, and the HE of A. satureioides revealed a synergistic action on P. larvae. The effective surfactin concentration in the mixture decreased from 32 to 1 μg ml(-1) and the HE concentration from 32 to 4 μg ml(-1), values similar or equal to minimal inhibitory concentrations observed for oxytetracycline. The fractional inhibitory concentration index confirmed synergism in 4 strains and partial synergism in one strain. The combination of surfactin synthesized by B. subtilis C4 and the HE from A. satureioides could be a natural alternative to help beekeepers to combat the American foulbrood agent P. larvae.

Anthelmintic effect of Mentha spp. essential oils on Echinococcus granulosus protoscoleces and metacestodes

The aim of the present work was to determine the in vitro effect of Mentha piperita and Mentha pulegium essential oils against Echinococcus granulosus and to compare the effectiveness of both oils according to the exposure time and concentration. Although both treatments had a protoscolicidal effect, M. pulegium had a considerably stronger effect than M. piperita. Essential oil of M. pulegium produced dose- and time-dependent effects. Maximal protoscolicidal effect was observed after 12 days of incubation and reached 0% after 18 days. This lack of viability was proved during the determination of infectivity into mice. Essential oil of M. piperita produced only a time-dependent effect. At 24 days p.i., the viability of protoscoleces decreased to approximately 50%. Scanning and transmission electron microscopy (SEM and TEM) demonstrated the drug-induced ultrastructural damage. On the other hand, a loss of turgidity was detected in all M. pulegium-treated cysts respective of the drug concentration. There was a correlation between the intensity of damage and the concentration of the essential oil assayed. Studies by SEM revealed that the germinal layer of treated cysts lost the feature multicellular structure. M. pulegium essential oil showed piperitone oxide as main compound in their composition, and we suggest that this component could be responsible of the markedly anthelmintic effect detected. Our data suggest that essential oils of Mentha spp. can be a promising source of potential protoscolicidal agents. The isolation of active anthelmintic constituents is in progress and may lead to the discovery of compounds with improved therapeutic value.

Repellent and acaricidal effects of botanical extracts on Varroa destructor

Extracts of indigenous plants from South America have shown a broad spectrum of bioactivities. No-contaminant and natural substances have recently resurged as control treatment options for varroosis in honey bee colonies from Argentina. The aim of this work was to evaluate the biological activity of botanical extracts from Baccharis flabellata and Minthostachys verticillata on Varroa destructor and Apis mellifera. The acaricidal and insecticidal activities were assessed by the spraying application method. Both ethanolic extracts showed high levels of toxicity against the mites and were harmless to their host, A. mellifera. During the attractive-repellent test, the olfactory stimulus evoked for the extract from B. flabellata resulted as a repellent for mites. The aromatic stimulus of these extracts would be strong enough to cause disturbance on the behavior of V. destructor. Thus, the repellent effect of these substances plus the toxicity on mites postulate these botanical extracts like promising natural compound to be incorporated for the control of varroosis.

Effect of bacterial metabolites on microsporidian Nosema ceranae and on its host Apis mellifera

Nosemosis, a disease caused by a microsporidian infection, is one of the most frequently observed parasitic pathologies affecting adult honeybees. Presently, Nosema ceranae seems to be the main microsporidian infection in Apis mellifera. The antibiotic fumagillin is the only compound available to treat Nosema diseases; however, it is no longer licensed in most EU member states; therefore, the need to identify new molecules/substances prevails. The intent of this paper is to test bacterial metabolites by Bacillus and Enterococcus strains, isolated from bee midgut and honey. The toxicity on bees and the antiparasitic activity on N. ceranae were assessed under laboratory conditions. Results did not yield toxicity for the administered surfactin or bacteriocin concentrations. Spores exposed to direct contact with a particular surfactin revealed a significant infectivity reduction when inoculated on bees. This surfactin, administered ad libitum from the individuals' emergence, led to a significant reduction in parasitosis development when bees were infected with untreated spores 7 days postemergence. Based on the results obtained, one of the surfactins is herein postulated as a molecule capable of reducing N. ceranae development, acting either by direct exposure to purified spores or incorporated into the digestive tract of the bee.

Acaricidal and insecticidal activity of essential oils on Varroa destructor (Acari: Varroidae) and Apis mellifera (Hymenoptera: Apidae)

Varroa destructor is an external parasitic mite that is a serious pest of honeybees and has caused severe losses of colonies worldwide. One of the feasible alternative treatments being used for their control is essential oils. The aim of this work was to evaluate the bioactivity of some essential oils on V. destructor and Apis mellifera in relation with their chemical composition and physicochemical properties. Lavender, lavendin and laurel essential oils showed linalool as main compound in their composition. 1,8-Cineole was also present as a predominant component in the laurel essential oil. However, thyme oil was characterized by a high concentration of thymol. Mites and bees toxicity was tested by means of complete exposure method. For mites, LC(50) values for laurel, lavender and lavendin essential oil did not show significant variation throughout all observation times. However, the LC(50) values for thyme oil at 48 and 72 h were lower than at 24 h. Bee mortality was evident only in treatment with thyme oil. At 48 and 72 h, lavender essential oil presented better selectivity indexes. In this research, all essential oils caused mite mortality without severe harmful effects on adult bees. The simultaneous evaluation of the physicochemical analysis of the essential oils, the characterization of the dosage response relationships among them, and the mortality effects on mite and bees, give us the possibility to obtain comparative results for future research in Varroa control.

Morphotypes of Varroa destructor collected in Apis mellifera colonies from different geographic locations of Argentina

Parasites display considerable phenotypic plasticity in life-history traits such as, body size. Varroa destructor is an ectoparasitic mite of the western honey bee Apis mellifera. Several studies have reported that in V. destructor, there is a wide phenotypic plasticity within a population of mites. However, it is unknown if there are morphologic variations in V. destructor populations affecting different A. mellifera populations. A morphometric study of V. destructor populations was conducted to provide information concerned to the relationships among parasite populations found in different geographic locations from A. mellifera colonies of Argentina. The hypothesis tested was different morphotypes of V. destructor populations parasitizing different A. mellifera populations from Argentina exist. A discriminant analysis employing eight morphologic variables revealed that it is possible to differentiate morphotypes of mites in Argentina. However, the level of discrimination detected among mites population varied according to the grouping of mite's population. Possible causes explaining the morphometric variability in the V. destructor populations were discussed.

First detection of Varroa destructor resistance to coumaphos in Argentina

In Argentina, studies on Varroa destructor resistance to coumaphos are still unknown. At present, high infestation levels of V. destructor are being detected in colonies of Apis mellifera after treatment with this acaricide. The aim of the present study was to determine the LC50 of coumaphos in V. destructor from four apiaries with high mite density after treatment with coumaphos. The LC50's were 112, 319, 127 and 133 microg/Petri dish for mites from the four apiaries. Significant LC50 differences were detected between resistant and susceptible mites. LC50 increased 197-559-fold when compared to the corresponding baseline, suggesting the development of resistance. These results are the first report of resistance to coumaphos in V. destructor in Argentina.

Evaluation of culture media for Paenibacillus larvae applied to studies of antimicrobial activity

This study was conducted to compare different liquid culture media for Paenibacillus larvae growth in order to find the best one to be used in studies on activity of antimicrobial substances, such as essential oils. P. larvae presented poor growth in usual broths such as Mueller-Hinton, commonly employed in antimicrobial activity assays. Growth in liquid media was evaluated using Paenibacillus larvae strains isolated from hives located in different geographical zones. The MYT medium (Mueller-Hinton broth, yeast extract and thiamine) was selected out of the eight liquid media analyzed, as it proved to be the most adequate due to its higher absorbance at 620 nm. The following mean values were obtained from the four P. larvae strains: 0.227 +/- 0.016 for the Cobo strain, 0.279 +/- 0.015 for La Plata strain, 0.758 +/- 0.020 for Mechongué strain and 0.244 +/- 0.0079 for Sierra de los Padres strain, respectively.

[Inhibition of Paenibacillus larvae employing a mixture of essential oils and thymol]

In vitro antimicrobial activity of a mixture of two essential oils and thymol against Paenibacillus larvae, causal agent of American Foulbrood (AFB), was evaluated. The essential oils were extracted from cinnamon (Cinnamomum zeylanicum) and thyme (Thymus vulgaris). The third component used, thymol, is the major component of the essential oil of thyme which contains 39.9% of thymol. Minimal inhibitory concentration (MIC) in Mueller-Hinton broth by the tube dilution method and minimal bactericide concentration (MBC) on MYPGP agar were evaluated. Thyme registered MIC values of 150-250 microg/ml and MBC values of 200-300 microg/ml, while the MIC and MBC values obtained for cinnamon were of 50-100 microg/ml and 100-125 microg/ml. Thymol showed similar MIC and MBC values of 100-150 microg/ml. No significant differences between the bacterial strains were detected, but significant differences between essential oils and thymol activity were registered (P<0,01). An inhibitory synergetic effect on AFB was observed reducing MIC and MBC values due to the use of a mixture of 62.5% of thyme, 12.5% of cinnamon and 25% of thymol.