Matías Maggi

Efficacy of natural propolis extract in the control of American Foulbrood

Paenibacillus larvae is the causative agent of American Foulbrood (AFB), a severe disease that affects larvae of the honeybees. Due to the serious effects associated with AFB and the problems related to the use of antibiotics, it is necessary to develop alternative strategies for the control of the disease. The aim of the present work was to evaluate the effect of a propolis ethanolic extract (PEE) against P. larvae and its potential for the control of AFB. In vitro activity of PEE against P. larvae isolates was evaluated by the disk diffusion method and the minimum inhibitory concentration (MIC) was determined. Toxicity for honeybees was evaluated by oral administration of PEE and its lethal concentration was assessed. Lastly, colonies from an apiary with episodes of AFB on previous years were divided into different groups and treated with sugar syrup supplemented with PEE by aspersion (group one), sugar syrup by aspersion (group two), fed with sugar syrup supplemented with PEE (group three) and fed with sugar syrup only (group four). All isolates were sensitive to PEE and the MIC median was 0.52% (range 0.32-0.64). PEE was not toxic for bees at least at 50%. Field assays showed that 21 and 42 days after the application of the treatments, the number of P. larvae spores/g of honey was significantly lower in colonies treated with PEE compared to the colonies that were not treated with PEE. To our knowledge, this is the first report about the use of propolis for the treatment of beehives affected with P. larvae spores.

Laboratory Evaluations of Syzygium aromaticum (L.) Merr. et Perry Essential Oil Against Varroa destructor

Abstract The oil obtained by hydrodistillation of the foral bottom of Syzygium aromaticum (L.) Merr. et Perry was analyzed by GC and GC/MS. Eugenol was the main constituent in the oil (86.7%). The biological activity of the oil applied to Varroa destructor and Apis mellifera was evaluated in two laboratory tests. Mite lethality was estimated using a complete exposure method test with the oil at different concentrations, and a systemic administration method of oil at different concentrations diluted in syrup was placed in feeders for bees. The LC50 for complete exposure method at 24 h was 0.59 μL/dish. The inferior and superior limits obtained were 0.47 x 10−6 μL/dish and 1.22 μL/dish, respectively. LC50 estimated at 48 h showed a slight decrease as compared to that recorded at 24 h. Ratio selection (LC50 of A. mellifera/LC50 of V. destructor) for complete exposure method was 26.46 and 13.35 for 24 h and 48 h, respectively. Regarding the systemic administration method, mites LC50 at 24 h was 12,300 ppm. The inferior and superior limits calculated were 9,214 ppm and 15,178 ppm, respectively. LC50 estimated at 48 h showed a slight decrease as compared to that recorded at 24 h. Ratio selection for systemic administration method was 3.05 and 2.22 for 24 h and 48 h, respectively. Syzygium aromaticum oil was found to be an attractant for V. destructor at 4.8% (w/w) concentration. The results showed that oil toxicity against V. destructor differed depending upon its administration. Nevertheless, the ratio selection calculated by this oil is expected to enable its application under field conditions with a good safety margin. This oil could also be used in combination with other oils in integrated pest management strategies in bee colonies.

Effects of the organic acids produced by a lactic acid bacterium in Apis mellifera colony development, Nosema ceranae control and fumagillin efficiency.

The European honey bee Apis mellifera is known to be affected by many parasites and pathogens that have great impact over the insect development. Among parasites affecting bee health, Nosema ceranae is one of the main biotic factors affecting colony populations. As honey bee populations decline, interest in pathogenic and mutualistic relationships between bees and microorganisms has increased. The main goal of the current study was to assess the effect of the oral administration of the metabolites produced by Lactobacillus johnsonii CRL1647 (mainly organic acids) supplemented in syrup, on: (I) N. ceranae sporulation dynamics before and after fumagillin application, and (II) performance of A. mellifera colonies. Different experiments were conducted to evaluate the effects of these bacterial metabolites on bees: in vitro administration revealed no toxic effects against bees. Colonies fed with the lactic acids incremented their beehive population and also the amount of fat bodies per bee. Finally, the organic acids reduced the intensity of the pathogen after the second application of treatment as well as enhanced the fumagillin efficiency. This study provides important information for the development of new control substances against nosemosis.

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.

Abscisic acid enhances the immune response in Apis mellifera and contributes to the colony fitness

The primary food of adult honey bees (Apis mellifera) is honey prepared by bees from nectar, provided by plants in order to stimulate the bee’s pollination service. Nectar consists of carbohydrates, amino acids and water, as well as other minor compounds whose proportion varies among plant species and whose biological implications in the honey bee physiology require intense research. Several environmental stressors are causing the decline of bee colonies, and thereby, we tried to connect the nutritional quality of bee’s diet with the strength of the bee’s immune system. The phytohormone abscisic acid (ABA) is present in nectar, honey and adult honey bees. It has been demonstrated that ABA stimulates innate immune defences in animal cells. However, the influence of ABA on A. mellifera’s health and fitness is unknown. Here, we show that honey bees fed with an ABA supplement in field experiments resulted in (i) the appearance of ABA in larvae and adult bees, (ii) enhanced haemocyte response to non-self recognition, (iii) improved wound healing and granulocyte and plasmatocyte activation and (iv) maximum adult bee population after the winter and increased pesticide tolerance. The results indicate that the naturally occurring compound ABA has a positive influence in honey bee immunity. ABA emerges as a potent booster of immune defence in A. mellifera and may be useful in addressing the colony losses threatening apiculture and pollination service worldwide.

Honeybee health in South America

Honeybees are essential components to modern agriculture and economy. However, a continuous increase in cases of colony losses and colony depopulation are being reported worldwide. This critical situation has put the fragile equilibrium between bees and plants on the edge. As a consequence, several scientists have begun to focus their lines of research on this issue. Most researchers agree that there is no single explanation for the observed colony losses. Instead, these losses result from a synergistic interaction between different stressors. South America is not the exception; several cases of colony losses and colony depopulation were reported by beekeepers throughout the continent, yet no accurate data has been published to date. Therefore, this article attempts to analyze the past and present situation of honeybee health in South America, specifically in Argentina, Chile, Uruguay, Brazil, and Venezuela. Furthermore, it is intended to serve as a comparison to future colony losses, as well as to provide guidance for future hypothesis-driven research on the causes of colony mortality. We evaluate the impact of the main parasites and pathogens affecting honeybee colonies and discuss the role of each with respect to reported honeybee losses. We also contemplate the main challenges that each nation must confront with regards to honeybee health.

Laboratory Evaluation of Heterothalamus alienus Essential Oil Against Different Pests of Apis mellifera

Abstract The Heterothalamus alienus oil was investigated in laboratory for control of different pests that affect the colonies of bees, Apis mellifera, against Varroa destructor mite, the bacterium that causes the American Foulbrood, Paenibacillus larvae and the fungus that produces the chalkbrood, Ascosphaera apis. The oil composition was analyzed by GC and GC/MS, the main components of the oil were β-pinene (44.4%) and trans-muurola-4(14),5-diene (9.2%). The concentration to kill 50% of the mites in 24 h (LC50) was 0.59 mg/cage. Inferior and superior limits were the following ones: 0.34 mg/cage and 1.01 mg/cage, LC50 was estimated for 48 h, and 72 h showed a slight increase with respect to the record of the 24 h. Paenibacillus larvae strains were Gram positive and catalase negative, the oil presented MIC values of 800–900 mg/L and MBC of 1000–1200 mg/L. Disks of impregnated flter paper with H. alienus oil around colonies of A. apis in growth inhibited the micelial growth signifcantly by 51% in the frst experiment (seven days) and by 31% in the second experiment (eight days).

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.

Apis mellifera haemocytes in-vitro, What type of cells are they? Functional analysis before and after pupal metamorphosis

Summary The honey bee Apis mellifera is affected by many parasites posing a serious threat to our ecosystem, agriculture and apiculture. The study of A. meliifera immune response represents a great complement for developing integrated disease management strategies. This work presents updated data concerning the in vitro cellular immune response of A. meliifera fifth instar larvae (L5) and newly emerged workers (W). Haemocytes from A. mellifera L5 and W clearly displayed different appearance in-vitro. The blood cells from these two developmental stages yielded behavioural differences regarding attachment and spreading. However, haemocytes extracted from L5 and W exhibited strong similarities with respect to their general (multicellular) behavioural pattern. This multi-haemolytic process, triggered after glass contact, could result from an encapsulation-like response. At the same time, an experimental system for studying A. mellifera cellular immunity in-vitro upon recognition of glass surfaces and haemolytic encapsulation response is herein developed.

Apis mellifera hemocytes generate increased amounts of nitric oxide in response to wounding/encapsulation

Apis mellifera populations are being threatened by several pathogens and parasitosis. Several authors have proposed that honey bee colonies may suffer from a compromised immune system leading to colony loss. This is why the study of A. mellifera immune system has become a topic of pressing concern. Nitric oxide (NO) is a signaling and immune effector molecule that has been proposed as a key molecule in invertebrate immunity, and that plays a part in A. mellifera cellular defenses. This paper deals with NO participation in the response to wounding/encapsulation challenge in A. mellifera fifth instar (L5) larvae. Challenging A. mellifera L5 larvae with nylon implants enhanced NO production and spreading in granulocyte-like hemocytes and increased the number of this NO-producing hemocyte type. However, AmNOS expression levels were not influenced by the insult. These results reveal that NO participates in the wound healing/encapsulation response as a signal molecule, possibly by the activation of a constitutively expressed AmNOS in honey bees.