In vitro antibacterial and antiparasitic effect of citrus fruit essential oils on the honeybee pathogen Paenibacillus larvae and the parasitic mite Varroa destructor.

FUSELLI, S;; MAGGI,M; GARCIA DE LA ROSA; PRINCIPAL, J.; EGUARAS, M; FRITZ, R

JOURNAL OF APICULTURAL RESEARCH

IBRA

Lugar: Londres; Año: 2009 vol. 48 p. 77 - 78

0021-8839

This work evaluates the in vitro bioactivity of grapefruit (Citrus paradisi Mac Fad) and sweet orange (Citrus sinensis L.Osbeck) essential oils as a potential control of V. destructor and P. larvae. Thirteen P. larvae strains were isolated from honey combs from hives exhibiting clinical symptoms of American foulbrood (AFB), in different regions of Argentina.  Citrus oil stock solutions used were of 3600, 3200, 2800, 2400 and 2000 mg/l. A twofold serial dilution was made and 100 ìl of a microbial biomass suspension of 107-108 cells/ml was added, the final concentrations being 2.34 mg/l, 2.08 mg/l, 1.82 mg/l, 1.56 mg/l and 1.30 mg/l. From a MIC negative microtitre plate, 100 ìl were transferred on MYPGP solid agar and incubated at 36±0.5 °C for 48 h, to determine minimal bactericide concentration (MBC) values. To test mortality of V. destructor, grapefruit and sweet orange oil solutions were prepared diluting 1, 2, 4, 8, 10, 30 and 40 ìl of each oil in 2 ml of ethanol. All P. larvae strains were highly susceptible to grapefruit oil with MIC and MBC mean values of all strains of 336.31 mg/l and 400.0 mg/ l, respectively. MIC and MBC mean values obtained for sweet orange were 800.0 mg/l and 933.33 mg/l, respectively. Fisher exact test results indicated highly significant differences between the essential oils tested (P< 0.01) and no significant differences between the P. larvae strains tested (P> 0.05). Neither grapefruit nor sweet orange essential oils produced mortality of honey bees at the concentrations tested. An increase in grapefruit oil concentration by eight times increased mite mortality from 15.0 % to 76.0 %. Sweet orange oil showed lower mortality values than those produced by grapefruit oil, mortality being only slightly increased even with a forty fold increase in concentration (Table 1). Mite mean LC50 for 24 h was 4.53 ìl/cage and 377.00 ìl/cage for grapefruit and sweet orange oils, respectively.