Pedro N. Bailac

An in vitro Evaluation of Tagetes minuta Essential Oil for the Control of the Honeybee Pathogens Paenibacillus larvae and Ascosphaera apis, and the Parasitic Mite Varroa destructor

Abstract Biological activity was evaluated of the Tagetes minuta essential oil in different in vitro laboratory experiments on the mite (Varroa destructor), honeybees (Apis mellifera), the bacterium that causes the American Foulbrood (Paenibacillus larvae), and the fungus that produces chalkbrood (Ascosphaera apis). Two methods of complete exposure were used for mite lethality test: by spraying in Burgerjons tower with 10 mg of active ingredient in solution with distilled water and emulsion, and in unmodified Petri dishes (60 x 20 mm) with oil (different concentrations) diluted in 1 mL of ethanol. Ratio selection was obtained as: LD50 of Apis mellifera/LD50 of V. destructor. Determination of Minimal Inhibitory Concentrations (MIC): to P. larvae was tested at concentrations of 25, 50, 100, 150, 200, 250, 350, 450, 500, 600, 650, 700, 800 and 1000 ppm. An A. apis strain was grown on agar MY20 supplemented with variable concentrations (between 0–800 ppm) of T. minuta oil was evaluated. Results obtained in tests of total exposure showed that the concentration was able to kill 50% of mites in 24 h (DL50) and was estimated to be 4.37 mg/cage. The efficacy after spray treatment reached 56%. The ratio selection was 3:11. Against P. larvae, the oil showed MIC values ranging from 700–800 μL/L depending on the tested bacterial strains. Tagetes minuta oil in agar MY20 inhibited mycelial growth of A. apis above concentrations of 200 ppm (p = 0.0001). Oil concentrations of 700 and 800 ppm achieved maximum growth inhibition of A. apis (67% of growth inhibition on average). Tagetes minuta oil demonstrated in vitro antibacterial, antifungical and miticide activity, although this oil shows a moderate inhibitor effect compared with other essential oils of native plants from Argentina. However, this oil presents a ratio selection that would allow it to be used in field conditions with a good safety margin. It is possible that this oil can be used in combination with others, in integrated pest management strategies in bee colonies.

Antimicrobial activity of Pimpinella anisum and Foeniculum vulgare essential oils against Paenibacillus larvae.

Abstract The essential oil obtained by hydrodistillation from the fruits of Pimpinella anisum L. (green anise) and Foeniculum vulgare Miller (fennel) were analyzed by GC and GC/MS and physicochemical properties. The oils of P. anisum and F. vulgare were found to be especially rich in (E)-anethole, 96.3% and 92.7%, respectively. The MICs were determined by the tube dilution method against Paenibacillus larvae. The oils showed MICs values were 300 µg/mL and 250 μg/mL for P. anisum and F. vulgare, respectively. Both oils presented great similarity in physiochemical properties values and antimicrobial activity.

In Vitro Activity of Essential Oils from San Luis-Argentina Against Ascosphaera apis

Abstract Chalkbrood is an invasive mycosis produced by Ascosphaera apis affecting exclusively the larvae growth of Apis mellifera L. There exists no pharmacological treatment and the chemical products used are not able to control the disease generating resistances and residues in the apicultural production. An ecological alternative is the use of essential oils as natural products to control this mycosis. Eight oils were screened against A. apis for fungicidal activity. The oils of Baccharis coridifolia and Eupatorium patens did not possess any activity while the oils of Tessaria absinthioides, Aloysia gratissima, Heterotheca latifolia, Lippia juneliana, L. integrifolia and L. turbinata exhibited varying levels of fungicidal activity.

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.

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).

Biological Activity of Heterotheca latifolia Essential Oil Against Varroa jacobsoni

Abstract The acaricidal effects and adult bee toxicity of Heterotheca latifolia essential oil on Varroa jacobsoni mites were evaluated. The oil was prepared as an emulsion and applied on the varroa females and on adult bees by pulverization in Burgerjons tower. Varroa lethality test was determined by 3%, 4% and 5% concentrations. The active ingredient was sprayed on the mites placed in groups of 10 on filter papers placed on a plastic dish. As controls, distilled water and water with the emulsifier were used. After spraying, mites were placed in an incubator at 33°±1°C and 70% RH. At these concentrations (3%, 4% and 5%) the oil showed a high mite mortality, while in the control group (water and water + emulsifier) the mortality was lower. Significant differences between control groups and tested groups were observed (p<0.05). At the highest concentrations (5%) H. latifolia oil did not show bee toxicity. Significant differences between control and tested groups were not observed (p>().()5). These results suggested that H. latifolia oil might play an important role in this honeybee parasitosis management.

Essential Oil of Lippia aff. juneliana Grown in San Luis, Argentina. Effect of Harvesting Period on the Essential Oil Composition

Abstract As a part of our research on essential oil composition of plants from San Luis, Argentina, we have examined the effect of harvesting period on the essential oil composition. The period ranging from February (summer) to April (autumn), gave the best yield in autumn. The oil from Lippia aff. juneliana (Mold.) Tronc. produced in the autumn was found to contain higher amounts of oxygenated compounds than the oil produced in summer. The oils have piperitenone oxide (22.9% and 47.7%), limonene (26.8% and 19.9%) and trans-dihydrocarvone (0% and 16.0%) as major components, respectively.

Essential Oil of Female Plants of Baccharis coridifolia De Candole

Abstract The essential oil of Baccharis coridifolia D.C., obtained by hydrodistillation of the aerial part of female plants in flowering-fructification, was analyzed by GC (retention indices) and GC/MS. The analysis revealed the presence of 29 compounds (89.2% of the oil) of which isocaryophyllene (34.3%), β-caryophyllene (10.8%), caryophyllene oxide (9.8%) and β-selinene (8.2%) were the major components

Essential Oil Composition of Wedelia glauca (Ort.) Hoffman ex Hicken from Argentina

Abstract The essential oil obtained by hydrodistillation from the aerial parts of Wedelia glauca (Asteraceae) growing in San Luis, Argentina, was analyzed by GC and GC/MS. Forty-two compounds were identified. The oil was found to be rich in monoterpene hydrocarbons (near 94.9%), such as limonene (38.0%), sabinene (23.9%) and α-pinene (22.0%), which were the main components.

Composition of the Essential Oils of Tessaria absinthioides (Hook et Arn.) D. Candole

Abstract The hydrodistilled oil from the fresh and dried aerial parts of Tessaria absinthioides was analyzed by a combination of GC and GC/MS. Thirty-three compounds representing 85% of the oil were identified. The main components of the oil were caryophyllene oxide (12.2%), (E)-β-damascenone (8.6%) and γ-eudesmol (8.5%). The oil consisted of about 32% oxygenated monoterpenes, 36% oxygenated sesquiterpenes and 17% sesquiterpene hydrocarbons. The ratio of oxygenated monoterpenes to oxygenated sesquiterpenes changed from 4.8 to 0.9 in oil of air-dried versus oil of fresh material