Jorge Augusto Marcangeli

The mite Varroa jacobsoni does not transmit American foulbrood from infected to healthy colonies

The present study was conducted to determine whether Varroa jacobsoni can transmit American foulbrood (AFB), caused by the bacterium Paenibacillus larvae to healthy colonies by the surface transport of spores. Five two-storey Langstroth colonies of Apis mellifera ligustica were infested by placing a sealed brood comb, with 10% Varroa prevalence, between the central brood combs of each colony. Two months later the colonies were inoculated with P. larvae by adding brood comb pieces with clinical signs of AFB (45±5 scales per colony). After 60 days the brood area was completely uncapped by means of dissecting needles and tweezers, separating the Varroa mites from the larvae and the collected mites were introduced at a rate of 51 per colony into four recipient hives placed in an isolated apiary. Twenty female Varroa specimens were separated at random and observed by SEM. Paenibacillus larvae spores were found on the dorsal shield surface and on idiosomal setae. All colonies died after 4–5 months due to a high incidence of varroosis. No clinical AFB symptoms or P. larvae spores were observed in microscopic preparations. It is concluded that Varroa jacobsoni does not transmit AFB from infected to healthy colonies; it does, however transport P. larvae spores on its surface.

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.

Influence of ‘parasitic intensity’ on Varroa jacobsoni Oud. reproduction

SUMMARYThe influence of ‘parasitic intensity’ (the number of adult female Varroa jacobsoni per cell) on mite reproduction in honey bee (Apis mellifera) colonies was studied during 1991 in Argentina. As the number of mites per cell increased, a clear decrease in the reproductive rate was observed from about three offspring per mite at 1 mite/cell to one offspring per mite at 6 mites/cell. There was also a decrease in the number of females reaching the adult stage. Parasitic intensity. was highest (up to 6 mites/cell) in winter and lowest in summer (up to 2 mites/cell). As the number of male offspring produced was not affected, changes in the sex ratio were observed. At a parasitic intensity of 1 mite/cell, there were 38.7% males in the offspring, but at 6 mites/cell the proportion of males was 51.3%. During winter, a lower number of brood cells were available resulting in a high proportion of highly infested cells and a reduced reproductive rate. It is suggested that exploitative competition could be one f...

Evaluation of the toxicity of a propolis extract on Varroa destructor (Acari: Varroidae) and Apis mellifera (Hymenoptera: Apidae)

Summary The effects of a propolis extract on Varroa destructor and Apis mellifera were evaluated by three different application methods: topical, spraying and oral. A propolis sample was extracted and its organoleptic and physic-chemically traits characterized. These analyses showed that it was a typical propolis from the Pampean region in Argentina, with elevated contents of biologically active compounds. Topical application was carried out by subjecting mites to contact with various propolis concentrations for different periods of time, which resulted in mortality and narcosis. Acaricidal effects were stronger with increasing concentrations of the propolis extracts. Spraying infested bees with a 10% propolis solution was harmless for bees but killed 78% of mites. Feeding infested bees with propolis extract in sugar syrup was not toxic to the mites but caused the death of bees treated with the highest concentration. Our results suggest that the propolis extracts from the Pampean Region could be incorporated into bee colonies by spraying, although the appropriate doses and concentrations to be administered, and the mechanism of action of the extracts on the mites are still to be elucidated.