Factors influencing host choice of the honey bee parasite Varroa jacobsoni Oud

Reproducing Varroa jacobsoni obtained from brood cells of Apis mellifera L. with 13–16 day old bees (pupae) and Varroa mites kept on adult bees for at least 8 days were simultaneously tested for their choice in three host types. Comparisons were made of attractiveness of Varroa jacobsoni to nurse bees, pollen foragers as to larvae from nearly capped brood cells. Host choices were observed in Petri dishes and in an Y-shaped olfactometer. Varroa jacobsoni obtained from capped brood cells showed a stronger preference for nurse bees in Petri dish simultaneous choice tests with pollen foragers or larvae than did mites which were previously kept on adult bees. In olfactometer simultaneous choice tests, the two mite test groups showed no clear difference in preferences for bees of different ages. The preference of Varroa jacobsoni for bees of different ages is therefore not only influenced by host factors but also by intrinsic factors in female mites that depend on the mite's reproductive stage.     

Effect of host brood type on the number of offspring laid by the honeybee parasite Varroa jacobsoni

The number of offspring laid by individual mites, varies depending on the type (drone or worker) of honeybee brood cell invaded. The number of offspring laid by individual mites increases when artificially transferred from worker to drone brood and vice versa when moved in the opposite direction.     

Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera)

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honeybee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 ± 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 ± 8.4%) and adult bees (3.5 ± 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83–96%) than in AHB in Brazil(25–57%), and similar to that found in EHB (76–94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

蜜蜂瓦螨敏感卫生行为研究进展

蜜蜂具有很高的生态价值和经济价值,对农业生产帮助巨大。然而,狄斯瓦螨Varroa destructor寄生给西方蜜蜂Apis mellifera蜂群造成重大损失,对蜜蜂健康构成严重威胁,因此,狄斯瓦螨的防治变得尤为紧要。虽然化学防治是防治狄斯瓦螨常用且有效措施,但仍存在许多缺点,如造成蜂产品污染、导致蜂螨产生抗药性等。另一方面,培育抗螨蜂种被证明是可持续的狄斯瓦螨防治方法。瓦螨敏感卫生行为(Varroa sensitive hygiene, VSH)是蜜蜂重要的抗螨性状之一。本文从狄斯瓦螨的生活周期、对蜜蜂的危害、蜜蜂抗螨行为、瓦螨敏感卫生行为调控和遗传育种等方面进行综述,为狄斯瓦螨防治和抗螨蜂种选育提供参考。     

Laboratory evaluation of some plant essences to control Varroa destructor (Acari: Varroidae)

This research was conducted to evaluate acaricidal effects of some plant essences on Varroa mites and the possibility of their usage for Varroa control. First, live Varroa mites were obtained from adult honeybees with CO₂ in a newly designed apparatus. Thyme, savory, rosemary, marjoram, dillsun and lavender essences at concentrations of 2 and 1g/100g (w/w), caused a mite mortality rate of more than 97% and 95%, respectively. Also spearmint at 2g/100g was able to kill more than 97% of Varroa mites. When sprayed on worker honeybees infected with mites, thyme, savory, spearmint and dillsun essences at 2g/100g (w/w) caused 43–58% Varroa mortality. Toxicity of thyme, savory and spearmint essences for worker honeybees was not significantly different from that of controls (acetone and water), but dillsun essence caused 12% honeybee mortality. These results showed that essences of thyme, savory and spearmint have acaricidal properties that could be used for controlling Varroa in honeybee colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Number of reproductive cycles of Varroa jacobsoni in honey-bee (Apis mellifera) colonies

Very little data exists concerning the number of reproductive cycles performed by individual Varroa mites. To understand the population dynamics of the Varroa mite it is necessary to know the number of fertile female offspring each Varroa female produces during her lifetime. The lifetime reproduction capacity of the mite consists of the mean number of fertile female offspring produced during each reproductive cycle multiplied by the mean number of cell passages. This paper describes an experimental design to estimate the number of reproductive cycles where mites are transferred to new mite-free colonies for reproduction in sealed brood cells. The data presented suggests that the mean number of reproductive cycles performed by the individual female mite is larger than previously accepted. Under optimal conditions, the mean number of reproductive cycles by Varroa females is probably greater than 1.5 but less than 2. Furthermore, the results show that the reproductive success of Varroa females going into cells to reproduce is not influenced by previous brood cycles.     

Varroa destructor reproduction during the winter in Apis mellifera colonies in UK

The reproductive behaviour of female Varroa destructor mites invading worker brood cells during the winter months (January to mid-March) was investigated in four Apis mellifera colonies in UK. The number of viable offspring produced during a reproductive cycle, per mite, was only 0.5 during winter compared with 1.0 during the summer. This was mainly due to a large increase in the population of non-reproductive mites (winter 20%, summer 8%). This increase can be explained by the high level of male offspring mortality observed in winter (42% vs. 18% in summer), which results in nearly half of the newly reared female mites being unfertilised. Since mites that do reproduce lay a similar number of eggs in winter ( ) as in summer ( ), and the level of mortality suffered by the first female offspring is similar in winter (7%) as in summer (6%), it is probably not the internal physiological state of the host which causes the high level of winter non-reproduction, as has been previously suspected.     

Selection for barriers between honey bees and a devastating parasite

Rivaling pesticides and a dearth of flowers, the parasitic mite Varroa destructor presents a tremendous threat to western honey bees, Apis mellifera. A longstanding, but minor, pest for the Asian honey bee Apis cerana, these obligate bee parasites feast on developing and adult A. mellifera across several continents. Varroa reproduction is limited to a short window when developing bee pupae are concealed in wax cells. Mated females target developing bees just before pupation and then have about one day to initiate reproduction, eventually laying one male and up to several female offspring. Female mites often fail to reproduce at all, instead waiting in cells until their bee host finishes development and then hitching dangerous rides on a succession of adult bees for up to several weeks, before scouting for a new host pupa. In this issue of Molecular Ecology, Conlon et al. (2019) have explored mite reproductive success via a clever and thought‐provoking association study. In so doing, they have identified a protein whose actions could be integral to the dance between bees and their mite parasites.     

Calorimetric investigations of the different castes of honey bees,Apis mellifera carnica

Summary Honey bees of different age and castes were investigated calorimetrically at 20, 25 and 30 °C. Experiments were completed by endoscopic observation of the insects in the visible and the near infrared range and by acoustical monitoring and subsequent frequency analysis of various locomotor activities. Direct calorimetric results of this paper are compared with data of indirect calorimetry from the literature using a respiratory quotient of 1.00 and 21.13 J consumed. Agreements between both methods are generally good. The results show that weight-specific heat production rates increase with age of worker bees by a factor of 5.6 at 30 °C, 3.7 at 25 °C and 40.0 at 20 °C. In groups of foragers the heat production decreases with growing group size to around 6% of the value for an isolated bee. The presence of a fertile queen or of brood reduces the heat output of a small worker group significantly. Adult drones exhibit a much higher metabolic rate (up to 19.7-fold at 20 °C) than juveniles with strong fluctuations in the power-time curves. Fertile queens show a less pronounced heat production rate than virgin queens (54% at 30 °C, 87% at 25 °C and 77% at 20 °C). Calorimetric unrest is much higher for young than for adult queens. Heat production is very low in both uncapped and capped brood and less than 30% of that of a newly emerged worker. In most cases temperature showed a significant influence on the metabolic level, although its sign was not homogeneous between the castes or even within them. Locomotor activities are easily recorded by the acoustic frequency spectrum (0–7.5 kHz) and in good agreement with endoscopic observations and calorimetric traces.Abbreviations RQ respiratory quotient - ww wet weight This paper is part of the PhD thesis of L.F.     

Varroa jacobsoni (Acari: Varroidae) is more than one species

Varroa jacobsoni was first described as a natural ectoparasitic mite of the Eastern honeybee (Apis cerana) throughout Asia. It later switched host to the Western honeybee (A. mellifera) and has now become a serious pest of that bee worldwide. The studies reported here on genotypic, phenotypic and reproductive variation among V. jacobsoni infesting A. cerana throughout Asia demonstrate that V. jacobsoni is a complex of at least two different species. In a new classification V. jacobsoni is here redefined as encompassing nine haplotypes (mites with distinct mtDNA CO-I gene sequences) that infest A. cerana in the Malaysia–Indonesia region. Included is a Java haplotype, specimens of which were used to first describe V. jacobsoni at the beginning of this century. A new name, V. destructor n. sp., is given to six haplotypes that infest A. cerana on mainland Asia. Adult females of V. destructor are significantly larger and less spherical in shape than females of V. jacobsoni and they are also reproductively isolated from females of V. jacobsoni. The taxonomic positions of a further three unique haplotypes that infest A. cerana in the Philippines is uncertain and requires further study.Other studies reported here also show that only two of the 18 different haplotypes concealed within the complex of mites infesting A. cerana have become pests of A. mellifera worldwide. Both belong to V. destructor, and they are not V. jacobsoni. The most common is a Korea haplotype, so-called because it was also found parasitizing A. cerana in South Korea. It was identified on A. mellifera in Europe, the Middle East, Africa, Asia, and the Americas. Less common is a Japan/Thailand haplotype, so-called because it was also found parasitizing A. cerana in Japan and Thailand. It was identified on A. mellifera in Japan, Thailand and the Americas.Our results imply that the findings of past research on V. jacobsoni are applicable mostly to V. destructor. Our results will also influence quarantine protocols for bee mites, and may present new strategies for mite control.     

Transfers ofVarroa mites from newly emerged bees: Preferences for age- and function-specific adult bees (Hymenoptera: Apidae)

Movements of the parasitic honey bee mite,Varroa jacobsoni (Oud.) were monitored in several assays as they moved among adult host honey bees,Apis mellifera. We examined the propensity of mites to leave their hosts and to move onto new bee hosts. We also examined their preference for bees of different age and hive function. Mites were standardized by selecting mites from newly emerged worker bees (NEWs). In closed jars, 50% ofVarroa left NEWs irreversibly when no physical path was present for the mites to return to the NEWs; about 90% of mites left newly emerged drones in identical assays. In petri dish arenas, mites were rarely seen off NEW hosts when monitored at 15-min intervals for 4 h; this was the case for single NEWs with one mite (NEWs+) and when a NEW+ and a NEW− (no mites) were placed together in a petri dish. When a NEW+ was held with either a nurse beeor a pollen forager, 25% of the mites moved to the older bees. When both a nurseand a pollen forager were placed in a petri dish with a NEW+, about 50% of the mites transferred to older bees; nurse bees received about 80% of these mites, whereas pollen foragers received significantly fewer mites (about 20%,P < 0.05). Most mite transfers occurred during the first 30 min after combining NEWs+ and test bees. When NEWs+ were combined with bees of known ages, rather than function, mites transferred more often to young bees than to older bees (1- and 5-day-old bees vs. 25-day-old bees,P < 0.05; 1-day-old vs. 13- and 25-day-old bees;P < 0.05). No differences in proportions of transferring mites were seen when the range of bee ages was ≤ 8 days (P > 0.05), implying that the factors mediating the mites’ adult-host preference change gradually with bee age. A possible chemical basis for host choice byVarroa is indicated by their greater propensity to move onto freezer-killed nurse bees than onto freezer-killed pollen foragers (P < 0.05) and by their lower movement onto heat-treated bees than onto control bees (P < 0.05). Bee age, hive function, and directional changes in cuticular chemistry are all correlated. Movements of newly emerged mites in relation to these variables may provide insights into their reproductive success inApis mellifera colonies.     

The natural control of the tracheal mite of honey bees

The natural control of the tracheal mite, Acarapiswoodi, of the honey bee depends greatly on good foragingopportunities for bee colonies and on limited competition between colonies. Thesevere, widely-publicised disease of bees, referred to as the Isle ofWight disease in Britain early in the last century when colonies weremore numerous than subsequently, was wrongly attributed to the mite, whichcauses no overt symptoms. The disease was almost certainly caused by beeparalysis virus, which does cause the symptoms and is independent of the mite,and which is similarly associated with large densities of bee colonies.     

Alarm pheromone perception in honey bees is decreased by smoke (Hymenoptera: Apidae)

The application of smoke to honey bee(Apis mellifera) antennae reduced the subsequent electroantennograph response of the antennae to honey bee alarm pheromones, isopentyl acetate, and 2-heptanone. This effect was reversible, and the responsiveness of antennae gradually returned to that of controls within 10–20 min. A similar effect occurred with a floral odor, phenylacetaldehyde, suggesting that smoke interferes with olfaction generally, rather than specifically with honey bee alarm pheromones. A reduction in peripheral sensitivity appears to be one component of the mechanism by which smoke reduces nest defense behavior of honey bees.     

Nonrandom visitation of brood cells by worker honey bees (Hymenoptera: Apidae)

The visitation pattern by worker honey bees to cells in the brood nest was monitored on an artificially created brood pattern consisting of about one-fourth brood cells evenly distributed among empty cells. The majority (63 %) of the observed workers selectively entered larval cells. In contrast, some workers avoided egg cells when presented a choice of egg vs empty cells. The results suggest that larvae produce a general signal indicating their presence to worker bees. Eggs also seem to produce a signal, which is perceived to be different from the one from larvae.     

Hirsutella thompsonii and Metarhizium anisopliae as potential microbial control agents of Varroa destructor,a honey bee parasite

The potential of Hirsutella thompsonii Fisher and Metarhizium anisopliae (Metschinkoff) as biological control agents of the parasitic mite, Varroa destructor Anderson and Trueman was evaluated in the laboratory and in observation hives. In the laboratory, time required for 90% cumulative mortality of mites (LT(90)) was 4.16 (3.98-4.42) days for H. thompsonii and 5.85 (5.48-7.43) days for M. anisopliae at 1.1 x 10(3) conidia mm(-2). At a temperature (34+/-1 degrees C) similar to that of the broodnest in a honey bee colony, Apis mellifera L., H. thompsonii [LC(90)=9.90 x 10(1) (5.86-19.35) conidia mm(-2) at Day 7] and M. anisopliae [LC(90)=7.13 x 10(3) (2.80-23.45) conidia mm(-2) at Day 7] both showed significant virulence against V. destructor. The applications of H. thompsonii to observation hives resulted in significant mortality of mites, and reduction of the number of mites per bee 21 and 42 days post-treatments. The treatments did not significantly affect the mite population in sealed brood. However, the fungus must have persisted because infected mites were still observed [82.97+/-(0.6)%] 42 days post-treatment. In addition, the fungus was found to sporulate on the host. A small percentage [2.86+/-(0.2)%] of dead mites found in the control hives also showed fungal infection, suggesting that adult bees drifted between hives and disseminated the fungus. H. thompsonii was harmless to the honey bees at the concentrations applied and did not have any deleterious effects on the fecundity of the queens. Microbial control with fungal pathogens provides promising new avenues for control of V. destructor and could be a useful component of an integrated pest management program for the honey bee industry.     

Behaviour of Varroa mites invading honey bee brood cells

Invasion behaviour of Varroa jacobsoni into honey bee brood cells was studied using an observation hive. The mites were carried close to a suitable brood cell by the bees. Subsequently, the mites moved from the bees to the rim of the cell, walked quickly inside, crawled between the larva and the cell wall, and moved onto the bottom of the cell. Varroa mites were never seen walking across the comb, and entering and leaving brood cells as has been described for Tropilaelaps clareae. Differences in invasion strategies between V. jacobsoni and T. clareae are discussed.