The bacterium Paenibacillus larvae and the mite Varroa destructor are two of the most severe biotic stressors affecting honeybees and are responsible for American foulbrood and varroosis respectively. To control these pathogens, beekeepers regularly apply synthetic acaricides or antibiotics to parasitized hives. However, antibiotic and acaricide overuse over time leads to resistance in bacteria strains and mite populations respectively, not to mention the residual contamination of bee products with these chemicals. The development of alternative and effective control methods of bee diseases is therefore crucial. In recent years, natural substances from plant extracts have emerged as the basis of suitable control methods to treat bee colonies parasitized by both P. larvae and V. destructor . Our aim was to evaluate the bioactivity of ethanolic and methanolic hop leaf extract (species: Humulus lupulus L, varieties: Victoria, Spalt, and Cascade) against P. larvae , V. destructor , and A. mellifera . The bactericidal activity against P. larvae was evaluated by the broth microdilution method. Topical administration protocols were used to determine the bioactivity of hop extracts on V. destructor and A. mellifera . Total polyphenols, flavonoids, saponins, and antioxidant capacity were determined for each hop leaf extract tested. The Victoria extract had the highest concentration of phenolic compounds, whereas Cascade and Victoria extracts had higher concentrations of the glycoside saponin. All hop extracts presented low toxicity against A. mellifera bees after 48 h of topical administration (except for Cascade ethanolic extract which reached a maximum of 36% of bee mortality). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranged from 0.69 to 2.75 mg/kg for the Cascade variety, 1.38 to 5.5 mg/kg for the Spalt variety, and 5.5 to 11 mg/kg for the Victoria variety. After 48 h, the acaricidal activity for the ethanolic extract of the Victoria variety reached a value close to 80%, while the methanolic extract of Cascade showed an acaricidal activity close to 70%. The results reported in this study support the potential use of methanolic and ethanolic extracts of hop leaves from Argentina as promising natural alternatives for varroosis and American foulbrood control.Paenibacillus larvae / Varroa destructor / Apis mellifera / natural extracts / Humulus lupulus / chemical composition
Although mitochondrial DNA mapping of Varroa destructor revealed the presence of several haplotypes, only two of them (Korean and Japanese haplotypes) were capable to infest Apis mellifera populations. Even though the Korean haplotype is the only one that has been reported in Argentina, these conclusions were based on mites sampled in apiaries from a specific geographical place (Buenos Aires province). To study mites from several sites of Argentina could reveal the presence of the Japanese genotype, especially considering sites near to Brazil, where Japanese haplotype was already detected. The aim of this work was to study the genetic structure of V. destructor populations from apiaries located in various provinces of Argentina, in order to determine the presence of different haplotypes. The study was carried out between January 2006 and December 2009. Phoretic adult Varroa mites were collected from honey bee workers sampled from colonies of A. mellifera located in Entre Ríos, Buenos Aires, Corrientes, Río Negro, Santa Cruz and Neuquén provinces. Twenty female mites from each sampling site were used to carry out the genetic analysis. For DNA extraction a nondestructive method was used. DNA sequences were compared to Korean haplotype (AF106899) and Japanese haplotype (AF106897). All DNA sequences obtained from mite populations sampled in Argentina, share 98% of similitude with Korean Haplotype (AF106899). Taking into account these results, we are able to conclude that Korean haplotype is cosmopolite in Argentina.
American foulbrood (AFB) is the most severe bacterial disease that affects honey bees, having a nearly cosmopolitan distribution. AFB's causative agent is Paenibacillus larvae. AFB kills infected honey bee larvae; however, it eventually leads to the collapse of the entire colony when left untreated. The infection takes place by the ingestion of the spores with the food provided by adult worker bees to the larvae. In South America (SA) the disease was first described in 1989 in Argentina, constituting the first sanitary challenge for beekeepers to overcome. Prevention and control measures of AFB in SA countries generally include vigilance for early diagnosis, isolation of apiaries with cases of AFB, and multiplication of healthy colonies with hygienic queens, among others. The extensive use of tetracycline hydrochloride in Argentina has led to the development of resistant P. larvae isolates. In this context, the development of alternative and effective methods for the control and prevention of AFB disease is crucial. Currently, alternative strategies for the prevention and treatment of AFB are being studied, mainly based on essential oils.
Aim of study: To evaluate the use of tannins extracts in the control of the American foulbrood pathology and to investigate if these extracts present levels of toxicity on Apis mellifera.Area of study: Paenibacillus larvae strains C1 and C2 were from Balcarce, province of Buenos Aires, strain C6 from Rio Cuarto, in Cordoba province and strain C9 from Concordia in Entre Rios province. Bees larvae used for toxicological assays were collected in Santa Paula experimental apiary, Mar del Plata (belonging to the Centro de Investigación en Abejas Sociales (CIAS-IIPROSAM) from UNMdP.Material and methods: The minimal inhibitory concentration (MIC) of five different tannin extracts were obtained by agar diffusion method on four P. larvae strains; using the MIC value, the toxicity test on A. mellifera larvae was performed afterwards.Main results: The MIC value was in the range of 6.9 to 898.6 µg/mL. Three tannin extracts did not show toxicity against bee larvae; however, those that were fed with the latter showed a significant increase in weight.Research highlights: Three tanninS extracts showed a good antimicrobial activity against P. larvae and they did not show toxicity against bee larvae.
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