Genotypic variation in susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Two-way selection for lines of honey bees (Apis mellifera L.) susceptible and resistant to infestation by tracheal mites (Acarapis woodi Rennie) was conducted for two generations. Individuals of the susceptible line were 1.4 and 2.4 times more likely to become infested by female mites after the first and second generations, respectively. These results demonstrate that genotypic variability exsts within North American populations and that selection for resistance is feasible. The mechanisms of resistance are unknown.     

Brood-cell size does not influence the susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Tracheal mites have been associated with the condition in honey bees that devastated colonies in Britain and Ireland in the early 1900s. The first outbreak of this condition, that became known as the ‘Isle of Wight’ disease, coincided with the period when brood-cell size was increased from about 5.0 mm to about 5.5 mm in width. We undertook an inoculation experiment over a 7-day period to establish if the act of increasing the brood-cell size could have triggered the onset of tracheal mites in honey bees. The standard-sized cells used had a cell width of 5.44 mm and the small-sized cells a width of 5.07 mm. Using callow (newly emerged) bees, from three colonies that had mixed cell sizes, we compared the susceptibility of bees reared in standard-sized cells with that of those raised in small-sized cells. The results indicated similar levels of female mite abundance (0.49 vs. 0.52 mites per bee) and mean fecundity (4.33 vs. 4.22 offspring per female mite), and produced no evidence of any difference in the overall susceptibility between the bees raised in the standard-sized cells versus small-sized brood cells.     

Effect of age of worker honey bees (Apis mellifera) on tracheal mite (Acarapis woodi) infestation

The susceptibility of worker honey bees,Apis mellifera L., as a function of age, to infestation by tracheal mites,Acarapis woodi Rennie, was investigated. Bees <24 h old were infested most frequently, and the frequency of infestation declined precipitously thereafter. Bees >4 days old were rarely infested in colonies during active brood rearing. Only 2 of 255 bees >8 days old, and 1 of 246 bees >16 days old, became infested. Most of the eggs found in bees>3 weeks old apparently were produced by the progeny of the original infestation.     

Comparative resistance in Buckfast and Canadian stocks of honey bees (Apis mellifera L.) to infestation by honey bee tracheal mites (Acarapis woodi (Rennie))

The results of bioassay and colony evaluation demonstrated that British and Texas Buckfast honey bee stocks had one-third to one-half the mean prevalence and abundance of tracheal mites as Canadian standard stock, indicating that Buckfast stocks are less susceptible to tracheal mites than Canadian standard stock. Hybrid Canadian and Buckfast stocks exhibited resistance characteristics similar to only one of their parental stocks, suggesting the colony has an unknown effect on the expression of a bee's resistance to mites. A high correlation (r _s=0.66) between abundance values from the bioassay and colony evaluations indicates that the bioassay can be used to screen bees for mite resistance.     

Distribution of the tracheal mite,Acarapis woodi,among the mesothoracic tracheal trunks of the honey bee,Apis mellifera

The selection of honey-bee tracheal trunks by host-seeking tracheal mites, Acarapis woodi, was examined in 307 samples of worker honey bees. The number of bees with 0, 1, and 2 infested tracheal trunks was determined for each sample and compared to an expected distribution based on the assumption that the probability that a tracheal trunk is infested is the same for all tracheal trunks. A Monte-Carlo simulation technique was employed to evaluate the significance of the test statistic. Observed distributions of bees with 0, 1, and 2 infested tracheal trunks were found to differ significantly from the expected distributions in 74 of the 307 samples. There were more uninfested bees and bilaterally infested bees than expected in all 74 cases. Further analysis revealed that the left and right tracheal trunks were equally likely to be infested.     

Acarapis mites of honey-bee,Apis mellifera in Iran

An extensive survey of colonies of the honey-bee, Apis mellifera, was conducted from December 1991 to February 1993 for the presence of both internal and external Acarapis mites in 21 provinces of Iran. Ten apiaries from each province and 5 hives/apiary were randomly selected for examination. A. woodi (R.) was found in 19 of the 139 apiaries sampled. The infested colonies were found in 7 of 21 provinces surveyed. Two external mites, A. dorsalis M. and A. externus M. were also found in honey-bee colonies in 8 provinces.     

Detection of honeybee tracheal mites (Acarapis woodi) by simple staining techniques

A total of 12 staining techniques, including five anionic and five cationic stains, and two mordant stains, were tested as possible histopathological methods for the detection of the honeybee tracheal mite, Acarapis woodi. The cationic stains stained the parasitic mites intensively and the ensheathing tracheae weakly positive in thin thoracic sections. The improved clarity and contrast of the stained mites within the tracheae in the thin thoracic sections facilitated the detection process. Even at very low levels of infestation, stained mites were detected easily and accurately under a dissecting microscope at a magnification as low as 10 ×. Consequently, examination of dissected trachae under a phase compound microscope, currently used for diagnosis of the mites, is no longer necessary. The stained specimen can also be mounted permanently on microslides.     

PCR-based detection of a tracheal mite of the honey bee Acarapis woodi

The effects of the tracheal mite Acarapis woodi on the health of honey bees have been neglected since the prevalence of Varroa mites to Apis mellifera colonies. However, tracheal mite infestation of honey bee colonies still occurs worldwide and could impose negative impact on apiculture. The detection of A. woodi requires the dissection of honey bees followed by microscopic observation of the tracheal sacs. We thus developed PCR methods to detect A. woodi. These methods facilitate rapid and sensitive detection of A. woodi in many honey bee samples for epidemiologic surveys.     

Regulation of nectar collection in relation to honey storage levels by honey bees, Apis mellifera

Honey bees collect distinct nutrient sources in the form ofnectar (energy) and pollen (nitrogen). We investigated the effectof varying energy stores on nectar and pollen foraging. We foundno significant changes in nectar foraging in response to changesin honey storage levels within colonies. Individual foragersdid not vary activity rates or nectar load sizes in responseto changes in honey stores, and colonies did not increase nectarintake rates when honey stores within the hive were decreased.This result contrasts with pollen foraging behavior, which isextremely sensitive to colony state. Our data show that individualforaging decisions during nectar collection and colony regulationof nectar intake are distincdy different from pollen foraging.The behavior of honey bees illustrates that foraging strategy(and therefore foraging models) can incorporate multiple currencies,including both energy and protein intake.[Behav Ecol 7: 286–291(1996)]     

Evaluation of sampling methods for determining infestation rates of the tracheal mite (Acarapis woodi R.) in colonies of the honey bee (Apis mellifera): Spatial,temporal, and spatio-temporal effects

Current sampling methods for estimating infestation rates of tracheal mites in colonies of the honey bee,Apis mellifera, assume that infested bees are randomly distributed and that temporal fluctuations in infestation rates occur homogeneously throughout the colony. We examined these assumptions. Samples of bees were collected from up to five locations in each of eight colonies, and colonies were sampled several times throughout the year. Estimates of infestation rates varied, depending on the location in the colony from which a sample was obtained. Temporal fluctuations in infestation rates did not always occur homogeneously with respect to sampling location. These results demonstrate that assumptions of current sampling protocols for estimating tracheal-mite infestation rates are often violated. Consequently, estimates derived using these methods may not be accurate, and conclusions based on such estimates may not be valid.     

Nocturnal dispersal by femaleAcarapis woodi in honey bee (Apis mellifera) colonies

Comparisons were made between the infestation levels of the honey bee tracheal miteAcarapis woodi (Rennie) in newly emerged honey bees (Apis mellifera L.) exposed for 12 h during the daytime or nighttime in mite-infested bee colonies. Bees exposed during the night harbored a significantly higher number of mites (718) when compared with the daytime bees (88 mites) (n=14 day/night cycles utilizing 33 colonies). On 4 days of an 8-day study, three test colonies were closed during the daytime to eliminate foraging flights. Thus equal numbers of bees were present in the colonies during the day and night sample periods. These 4 flightless days were compared to 4 free-flight days and mite dispersal rates were not significantly different. Additionally, the movement of bees on the combs of four glass-walled observation hives was quantified on 10 days at 0800, 1200, 1600, 2000, 2400 and 0400 h. Bee movement at 2400 and 0400 h was significantly lower than the other observation times. Movement of host bees may be one factor involved in the increased nighttime mite dispersals. These findings do not support the hypothesis that the absence of foraging bees during the day reduces the bee to bee contact time, thus reducing mite dispersals between host bees. Differential diurnal activity levels between host bees and mite parasites was demonstrated. The exact role of host-bee behavior and/or mite behavior in the nighttime dispersal patterns observed, remains for further investigation.     

Enterobacteriaceae isolated from foraging worker honey bees,Apis mellifera

Enterobacter cloacae, Escherichia coli, Enterobacter aerogenes, Shigella sp., and Klebsiella pneumoniae were isolated from the intestinal contents of healthy foraging adult worker honey bees, Apis mellifera, in Tucson, Arizona. Three cultures could not be identified. Pseudomonadaceae and Erwinia organisms were not found.     

Host preference of the honey bee tracheal mite (Acarapis woodi (Rennie))

Field and laboratory bioassays were used to test the preference of the honey bee tracheal mite,Acarapis woodi (Rennie), for drones versus workers. Groups of newly-emerged drones and workers were marked and introduced into either heavily infested colonies (field bioassays) or into the cages of infested bees obtained from the field colonies (laboratory bioassays). Seven days later all of the marked bees in each bioassay were removed. The numbers of mites of each life stage in each drone or worker target bee of each experiment were quantified. Mite prevalence values for the two castes were not found to differ significantly for either experiment. However, the caste of the target bee was shown to influence the migration of the adult female mites. Drones contained a greater number of migratory female mites and greater total numbers of all mite stages as compared to workers. These results indicate that migrating female mites preferentially infest drones and suggest that the role of drones in the dissemination and population dynamics of the tracheal mite needs to be examined further.     

Nosema ceranae in European honey bees (Apis mellifera)

Nosema ceranae is a microsporidian parasite described from the Asian honey bee, Apis cerana. The parasite is cross-infective with the European honey bee, Apis mellifera. It is not known when or where N. ceranae first infected European bees, but N. ceranae has probably been infecting European bees for at least two decades. N. ceranae appears to be replacing Nosema apis, at least in some populations of European honey bees. This replacement is an enigma because the spores of the new parasite are less durable than those of N. apis. Virulence data at both the individual bee and at the colony level are conflicting possibly because the impact of this parasite differs in different environments. The recent advancements in N. ceranae genetics, with a draft assembly of the N. ceranae genome available, are discussed and the need for increased research on the impacts of this parasite on European honey bees is emphasized.