Impacts of dietary supplementation with p-coumaric acid and indole-3-acetic acid on survival and biochemical response of honey bees treated with tau-fluvalinate.

Pollinator populations are in decline worldwide. Multiple factors have been cited as potential causes to these declines. In honey bees, a combination of stressors is known to cause colony losses. Adequate nutrition is a key factor for honey bee growth and colony development. Several studies show that the nutritional quality of the diet is directly proportional to the ability of the bee to face challenges or stressors. We explored the effect of p-coumaric (600 µM) and indole-3-acetic acid (2, 20 or 200 µM) supplementation on the survival and activity of key detoxification enzymes of honey bees exposed to tau-fluvalinate. The dietary supplementation with p-coumaric and indole-3-acetic acids (20 µM) enhanced the survival of bees exposed to tau-fluvalinate (approximately 20%). We also showed that dietary p-coumaric acid increased the levels of cytochrome P450 and glutathione reductase activity in bees treated with tau-fluvalinate, as well as in the untreated controls, while glutathione-S-transferase activity was lower in treated bees than in untreated. In bees fed with indole-3-acetic acid, cytochrome P450 showed increased levels, however, glutathione-S-transferase showed the lowest activity. Moreover, the results showed that supplementation with p-coumaric and indole-3-acetic acids did not alter acetyl cholinesterase activity, nor did treatment with tau-fluvalinate. Altogether, the enzymatic changes related to the detoxification mechanisms observed in bees that were fed with p-coumaric and indole-3-acetic acids could be responsible for the increased survival of bees treated with tau-fluvalinate compared to those that received a control diet. The results presented in this study, together with previous studies, provide evidence of the importance of dietary phytochemicals in the response of honey bees to pesticide exposure. Moreover, these results are the first report of the beneficial effect of the phytohormone indole-3-acetic acid on the survival of honey bees treated with tau-fluvalinate.

Physicochemical parameters and sensory properties of honeys from Buenos Aires region.

The physicochemical parameters (moisture, hydroxymethyl furfural, colour, electrical conductivity, free acidity, glucose, fructose and sucrose) and the sensory properties(aroma, taste, appeareance, texture) were determined in honeys from apiaries of the agricultural, hills and meadow zones of the south east region of Buenos Aires province (Argentina). The analysis of variance showed significant differences among zones in the mean value of hydroximethyl furfural, colour, electrical conductivity and sucrose content. The principal component analysis explained the 70% of the variance among samples with the first two principal components in both cases. The cluster analysis and linear discriminant analysis showed that samples were grouped in relation to the sampling region coinciding with the results of the principal component analysis. Results suggest that could be possible to classify honeys according to the geographic origin based on the physicochemical parameters; however, the sensory properties were not good predictors.

Body size variability of Varroa destructor and its role in acaricide tolerance.

Phenotypic plasticity has been defined as the ability of a genotype to produce different phenotypes when exposed to distinct environments throughout its ontogeny. Morphological variability of individuals is an example of this plasticity. Taking into account that several studies have reported a wide morphological variability in Varroa destructor populations, we evaluated if the body size plasticity of the parasite constituted a key factor able to modulate mites survival when they were exposed to a drug bioassays. Drug bioassays against mites were conducted using three different Syzygium aromaticum essential oil concentrations (0.5, 1, and 5 µl/capsule) and controls. After 4 h of exposition, mite mortality was registered. The width (WS) and length (LS) of the dorsal shield were measured in dead mites. General lineal models were carried to determine if V. destructor survival to acaricides was related to the explanatory variables. Data modelling confirmed that WS and LS variables, together with time interaction, were significantly related to V. destructor survival when the parasites were exposed to acaricides. The models proposed demonstrated that for the smaller S. aromaticum essential oil concentration, the larger the parasite body, the greater the probability that it remains alive at the end of the bioassay. Such relationship was inverse for the other two concentrations tested. Possible causes explaining the body size variability in V. destructor individuals were discussed.

Susceptibility of Varroa destructor (Acari: Varroidae) to synthetic acaricides in Uruguay: Varroa mites' potential to develop acaricide resistance.

The purpose of this study was to estimate the acaricide susceptibility of Varroa destructor populations from Uruguay, which had never been exposed to synthetic acaricides. It was also to determine whether acaricide resistance to coumaphos occurred in apiaries in which acaricide rotation had been applied. Bioassays with acaricides against mite populations that had never been exposed to synthetic acaricides were performed, also against mite populations in which control failures with coumaphos had been reported. Additionally, coumaphos' effectiveness in honeybee colonies was experimentally tested. The lethal concentration that kills 50% of the exposed animals (LC(50)) for susceptible mite populations amounted to 0.15 µg/Petri dish for coumaphos and to less than 0.3 µg/Petri dish for the other acaricides. Coumaphos LC(50) was above 40 µg/Petri dish for resistant mites. The effectiveness of coumaphos in honeybee colonies parasitized by V. destructor ranged from 17.6% to 93.9%. LC(50) for mite populations susceptible to the most commonly applied miticides was determined, and the first case of coumaphos resistance recorded in Uruguay was established.

Resistance phenomena to amitraz from populations of the ectoparasitic mite Varroa destructor of Argentina.

In Argentina, Varroa destructor resistance to coumaphos has been previously reported. However, the status of mite susceptibility to other hard acaricides is still unknown. At present, high infestation levels of V. destructor are being detected in colonies of Apis mellifera after treatment with amitraz. The aim of the present study was to determine the LC(50) of amitraz in V. destructor from three apiaries with high mite density after treatment with the acaricide. The LC(50) values were 3.9, 3.5, and 3.7 µg/Petri dish for mites from three different apiaries. Significant LC(50) differences were detected between resistant and susceptible mites. LC(50) increased 35-39-fold when compared to the corresponding baseline, suggesting the development of resistance. These results are the first report of resistance to amitraz in V. destructor in Argentina and extend the knowledge according to the status of acaricides resistance in the country.

Brood cell size of Apis mellifera modifies the reproductive behavior of Varroa destructor.

We undertook a field study to determine whether comb cell size affects the reproductive behavior of Varroa destructor under natural conditions. We examined the effect of brood cell width on the reproductive behavior of V. destructor in honey bee colonies, under natural conditions. Drone and worker brood combs were sampled from 11 colonies of Apis mellifera. A Pearson correlation test and a Tukey test were used to determine whether mite reproduction rate varied with brood cell width. Generalized additive model analysis showed that infestation rate increased positively and linearly with the width of worker and drone cells. The reproduction rate for viable mother mites was 0.96 viable female descendants per original invading female. No significant correlation was observed between brood cell width and number of offspring of V. destructor. Infertile mother mites were more frequent in narrower brood cells.

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.

LD50 and repellent effects of essential oils from Argentinian wild plant species on Varroa destructor.

The repellent and acaricidal effects of some essential oils from the most typical wild plant species of northern Patagonia, Argentina, on Varroa destructor Anderson & Trueman were evaluated using a complete exposure test. Honey bees, Apis mellifera L., and mites (five specimens of each per dish) were introduced in petri dishes having different oil concentrations (from 0.1 to 25 micro per cage). Survival of bees and mites was registered after 24, 48, and 72 h. An attraction/repellence test was performed using a wax tube impregnated with essential oil and another tube containing wax only. The lowest LD50 values for mites were registered for Acantholippia seriphioides (A. Gray) Mold. (1.27 microl per cage) and Schinus molle L. (2.65 microl per cage) after 24 h, and for Wedelia glauca (Ortega) O. Hoffm. ex Hicken (0.59 microl per cage) and A. seriphioides (1.09 microl per cage) after 72 h of treatment. The oil with the highest selectivity ratio (A. mellifera LD50/V. destructor LD50) was the one extracted from S. molle (>16). Oils of Lippia junelliana (Mold.) Troncoso, Minthostachys mollis (HBK) Grieseb., and Lippia turbinata Grieseb. mixed with wax had repellent properties. None of the oils tested had attractive effects on Varroa mites.

Evaluation of the time of uncapping and removing dead brood from cells by hygienic and non-hygienic honey bees.

Most research on hygienic behavior has recorded the time taken by the colony to remove an experimental amount of dead brood, usually after one or two days. We evaluated the time that hygienic (H) and non-hygienic (NH) honey bees take to uncap and remove dead brood in observation hives after the brood was killed using the pin-killing assay. Four experimental colonies were selected as the extreme cases among 108 original colonies. Thirty brood cells were perforated with a pin in two H and two NH colonies and observations were made after 1, 2, 3, 4, 5, 6, and 24 h. Different stages of uncapping and removing were recorded. Differences in uncapping and removal between H and NH colonies were significant for all comparisons made at the different times after perforation. Using observation hives one obtains a better and faster discrimination between H and NH colonies than in full size colonies. It is possible to differentiate H and NH within a few hours after perforating the cells.