Varroa Infestation Research Articles

Varroa jacobsoni infestation of adult Africanized and Italian honey bees (Apis mellifera) in mixed colonies in Brazil

Different levels of infestation with the mite Varroa jacobsoni have been observed in the various Apis mellifera races. In general, bees of European races are more susceptible to the mite than African honey bees and their hybrids. In Brazil honey bee colonies are not treated against the mite, though apparently both climate and bee race influence the mite infestation. Six mixed colonies were made with Italian and Africanized honey bees. The percentage infestation by this parasite was found to be significantly lower in adult Africanized (1.69 ± 0.44) than Italian bees (2.79 ± 0.65). This ratio was similar to that found in Mexico, even though the Africanized bees tested there had not been in contact with varroa, compared to more than 20 years of the coexistence in Brazil. However, mean mite infestation in Brazil on both kinds of bees was only about a third of that found in Mexico.

Temperature profiles of the brood nests of Apis cerana and Apis mellifera colonies and their relation to varroosis

SUMMARYTemperatures in the brood nests of Apis mellifera mellifera and Apis cerana indica were compared. Within the centre we found similar temperatures in worker brood cells, at external temperatures between 18°-33°C. At the periphery of the brood nest, where drone brood usually is located, temperature in brood cells of A. cerana was clearly lower compared to A. mellifera. Average temperature in drone brood cells was 0.4°C lower compared to nearby worker brood cells. While temperature in worker brood cells of A. mellifera colonies was close to 35°C, temperature in drone brood cells of A. cerana colonies was only 33°C, at ambient temperatures in Sabah (Malaysian Borneo). On its original host A. cerana, the parasite Varroa jacobsoni reproduces nearly exclusively in capped drone brood cells. This explains why the parasite has its reproductive optimum at 33°C. ‘Temperature jumps’, discussed in previous publications as a mechanism by which A. cerana colonies could defend themselves against varroa infestations, were found to be artifacts caused by reactions of the bees to the temperature measurement device.

A short test evaluating larval attractiveness of honey bees toVarroa jacobsoni

SUMMARYA controlled experiment which utilized a larval transfer (grafting) technique was used to evaluate attractiveness of larvae from four different stocks of honey bees (Apis mellifera) to Varroa jacobsoni. The stocks of honey bees were: ARS-Y-C-1 (A. m. carnica, from Yugoslavia), Hastings (A. m. carnica, from Canada), an F1 hybrid between ARS-Y-C-1 and Hastings, and a Louisiana stock. Newly hatched larvae (target larvae) from each test stock were grafted into an area at the centre of a brood frame occupying 8 rows of 20 cells (160 cells). After larval transfer, each brood frame containing target larvae was introduced into a Varroa-infested colony. Inspection of the frames 2 weeks later showed that ARS-Y-C-1 pupae were less frequently infested than Hastings and Louisiana pupae (20% vs. 36% and 40%), while the infestation rate of the hybrids was intermediate (29%). The stocks did not differ in other parameters of Varroa infestation (mite load per infested pupa, number of females per infested pupa, numbe...

Field trials of treatments againstVarroa jacobsoniusing fluvalinate and flumethrin strips in honey bee colonies containing sealed brood

SUMMARYThe effectiveness of half the recommended dose of fluvalinate (Apistan) and flumethrin (Bayvarol) against Varroa jacobsoni was tested in honey bee colonies containing sealed brood. The experiment was carried out in Zaragoza, Spain, in five apiaries of 15 hives each, containing colonies of Apis mellifera mellifera. Each apiary was divided into three groups. Hives in one group were each treated with a polyvinyl chloride (PVC) strip containing 0.8 g of fluvalinate. Hives in the second group each received two polyethylene strips each containing 3.6 mg of flumethrin. The third group served as a control and received no treatment. Treatment strips were left in the hives for 28 days. Varroa infestation rates were measured in adult bees and sealed brood before and after the treatment. Both of the tested acaricides reduced the infestation rate to practically zero in both adult bee and sealed brood Infestations. Infestation rates in the two groups of treated colonies were significantly different from those in control colonies, in which the varroa populations showed irregular but Increasing infestation rates. The results show that Apistan and Bayvarol can be used successfully for a period of 28 days, in the presence of sealed brood, at half the dose suggested by the manufacturers.

Residue determination for some products used against Varroa infestation in bees

Determination des residus de quelques acaricides utilises contre la varroatose. Pendant une periode de 3 ans, de 1987 a 1989, des experiences ont porte sur des acaricides utilises contre Varroa jacobsoni: le bromopropylate, le thymol, l'amitraze et le fluvalinate (tableau I). Les traitements ont ete realises a l'automne sur 171 colonies situees dans des localites de la plaine d'Italie du Nord

Variance and Heritability of the Capped Developmental Stage in EuropeanApis MelliferaL. and Its Correlation with IncreasedVarroa JacobsoniOud. Infestation

SummaryA time-saving method for determining the duration of the capped stage (sealed brood) of large numbers of colonies is described. The results of 112 colonies covering 22 different origins and hybrids of European honeybee races are presented. Differences up to 9 h between strains and up to 19 h within individual colonies could be detected. Influenced by seasonal effects, the average capped period is about 7 h shorter in early than in late summer. For one group of test colonies (n= 21) the Varroa infestation after 18 months of undisturbed colony and mite population development has been determined. The correlation between the capped period and the susceptibility of the colonies to mites is calculated as r = 0·48. By linear regression, an 8·7% reduction of the final mite infestation is calculated for a 1-h reduction of the capped period. The heritability of the duration of the capped period is estimated with h2 = 0·232. This may be a realistic value for test populations of European honeybee under field conditions.

Differential Reproduction of the Mite, Varroa jacobsoni (Mesostigmata: Varroidae), on Africanized and European Honey Bees (Hymenoptera: Apidae)

Recent surveys of honey bee colony mortality due to the external parasite Varroa jacobsoni (Oudemans) suggest that the virulence of this mite pest may be affected by climate or honey bee race. The latter possibility was tested by examining the effect of varroa infestation on colonies of Africanized and European bees in Brazil. Infestation of varroa on colonies of both bees was similar, but there were significant differences between percentages of mites that reproduced. In European bee colonies, 75% of infested brood cells had immature mites compared with only 49% of infested brood cells in colonies of Africanized bees. Decreased rate of varroa reproduction on Africanized honey bee worker brood is one factor contributing to reduction of virulence of varroa in Africanized bee colonies. The role of a second factor, length of honey bee pupal state, also is discussed. Honey bee race rather than differences in climate appears to play a crucial role in resistance to varroa.