Effect of pollen extract supplementation on the varroatosis tolerance of honey bee (Apis mellifera) larvae reared in vitro

Parasite and virus dynamics in the honeybee Apis mellifera unicolor on a tropical island recently invaded by Varroa destructor

In La Réunion, the established honeybee subspecies Apis mellifera unicolor, an endemic subspecies of African lineage, is facing considerable challenges. Since the introduction of the Varroa destructor mite in 2017 high colony losses have been recorded. We investigated the dynamics of V. destructor and two viruses, the Deformed Wing Virus (DWV), known to be transmitted by the mite, and the Chronic Bee Paralysis Virus (CBPV), in A. m. unicolor. Colonies from two apiaries located at 300 and 900 m a.s.l were monitored twice for one year without any acaricide treatment. The brood area, V. destructor infestation rates, DWV and CBPV prevalence and load were recorded monthly. A. m. unicolor maintained brood rearing throughout the year. Varroa destructor infestation resulted in high colony mortality (up to 85 %) and high phoretic mite rates (up to 52 mites per hundred bees). The establishment of DWV in colonies occurred after that of V. destructor and the mite infestation rate had a significant effect on the virus prevalence and load. CBPV appeared only transiently throughout the surveys. The data showed that, in tropical colonies with permanent brood rearing, V. destructor and DWV can reach high levels, but are still subject to seasonal variations that appear to be influenced by environmental conditions. This suggests that beekeeping practices could be adapted by favouring sites and periods for transhumance or acaricide treatment.

Effectiveness of electric harps in reducing Vespa velutina predation pressure and consequences for honey bee colony development

BACKGROUND

Vespa velutina has become a species of concern in invaded regions of Europe and Asia, due to its impacts on biodiversity, apiculture and society. This hornet, a ferocious hunter of pollinating insects, poses a serious threat to biodiversity and pollination services. Despite ongoing efforts, its extermination in continental Europe is hampered by a lack of effective control methods, thus effective mitigation measures are primary concerns. The aims of this work were: (i) to study the effects of V. velutina predating on honey bee colonies, and (ii) to assess the effectiveness of electric harps in reducing hunting pressure and predation. We assessed the predation pressure and compared honey bee colony performance, body weight of workers, and winter survivorship for protected versus unprotected colonies in 36 experimental hives across three apiaries.

RESULTS

Electric harps protected honey bees by reducing predation pressure and therefore mitigating foraging paralysis. Consequently, foraging activity, pollen income, brood production and worker body weight were higher in protected colonies which in turn showed greater winter survivorship than those that were unprotected, especially at sites with intermediate to high levels of predation.

CONCLUSION

The predation of V. velutina affects foraging activity, breeding, body weight and colony survivorship of Apis mellifera. Electric harps contribute significantly to mitigate the impact of this invasive hornet on apiaries; however, they should be deployed in tandem with additional measures to preserve honey bee colony stocks, such as facilitating access to food sources for colonies during the periods of highest predation pressure. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Transmission of deformed wing virus between Varroa destructor foundresses, mite offspring and infested honey bees

Background

Varroa destructor is the major ectoparasite of the western honey bee (Apis mellifera). Through both its parasitic life-cycle and its role as a vector of viral pathogens, it can cause major damage to honey bee colonies. The deformed wing virus (DWV) is the most common virus transmitted by this ectoparasite, and the mite is correlated to increased viral prevalence and viral loads in infested colonies. DWV variants A and B (DWV-A and DWV-B, respectively) are the two major DWV variants, and they differ both in their virulence and transmission dynamics.

Methods

We studied the transmission of DWV between bees, parasitic mites and their offspring by quantifying DWV loads in bees and mites collected in in vitro and in situ environments. In vitro, we artificially transmitted DWV-A to mites and quantified both DWV-A and DWV-B in mites and bees. In situ, we measured the natural presence of DWV-B in bees, mites and mites’ offspring.

Results

Bee and mite viral loads were correlated, and mites carrying both variants were associated with higher mortality of the infected host. Mite infestation increased the DWV-B loads and decreased the DWV-A loads in our laboratory conditions. In situ, viral quantification in the mite offspring showed that, after an initially non-infected egg stage, the DWV-B loads were more closely correlated with the foundress (mother) mites than with the bee hosts.

Conclusions

The association between mites and DWV-B was highlighted in this study. The parasitic history of a mite directly impacts its DWV infection potential during the rest of its life-cycle (in terms of variant and viral loads). Regarding the mite’s progeny, we hypothesize that the route of contamination is likely through the feeding site rather than by vertical transmission, although further studies are needed to confirm this hypothesis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05463-9.

Effects of Three Types of Pollen on the Growth and Development of Honey Bee Larvae (Hymenoptera, Apidae)

Pollen serves as an essential protein source for honey bee larvae. The nutrients in pollen greatly influence larval growth and development. Here, the survival, prepupal weight, developmental stage, pollen digestibility and midgut cells in honey bee (Apis mellifera L.) larvae were evaluated by performing in vitro and 5-ethynyl-2′-deoxyuridine (EdU) assays on larvae reared on three single pollens (Brassica napus L., Armeniaca sibirica L., and Pyrus bretschneideri Rehd.) and a pollen mixture (mixture of the three pollens in equal proportions). The results showed that the survival rate of larvae fed 10 mg of rape pollen was lowest (P < 0.05), but there were no notable differences in the survival rate among the groups receiving the other types and doses of pollen (P > 0.05). The prepupal weight of larvae fed apricot pollen was significantly lower than those of the other groups (P < 0.05). The digestibility of rape pollen and the pollen mixture were dramatically higher than those of apricot and pear pollen (P < 0.05). Pear and mixed pollen exerted negative effects on the nuclear area of midgut cells in the early larval stage (P < 0.05). In conclusion, detection of larval midgut cells using the EdU assay might be an effective method to assess the pollen nutritive value in honey bees. Compared to apricot and pear pollen, rape pollen was more beneficial in larval honey bee growth and development.

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives-A Review

Varroa destructor is a real challenger for beekeepers and scientists: fragile out of the hive, tenacious inside a bee colony. From all the research done on the topic, we have learned that a better understanding of this organism in its relationship with the bee but also for itself is necessary. Its biology relies mostly on semiochemicals for reproduction, nutrition, or orientation. Many treatments have been developed over the years based on hard or soft acaricides or even on biocontrol techniques. To date, no real sustainable solution exists to reduce the pressure of the mite without creating resistances or harming honeybees. Consequently, the development of alternative disruptive tools against the parasitic life cycle remains open. It requires the combination of both laboratory and field results through a holistic approach based on health biomarkers. Here, we advocate for a more integrative vision of V. destructor research, where in vitro and field studies are more systematically compared and compiled. Therefore, after a brief state-of-the-art about the mite's life cycle, we discuss what has been done and what can be done from the laboratory to the field against V. destructor through an integrative approach.

The nature of the arena surface affects the outcome of host-finding behavior bioassays in Varroa destructor (Anderson & Trueman)

Varroa destructor, an acarian parasite of the Western honey bee Apis mellifera L., is a serious threat to colonies and beekeeping worldwide. The parasite lifecycle occurs in close synchrony with its host development. The females have to discriminate between different developmental stages of the host and trigger an appropriate behavioral response. Many studies have focused on these behavioral aspects, whether it is the choice of a precise host stage or the reproduction of female mites. Behavioral tests often require laboratory settings that are very different from the mite's environment. Our first experiment was designed to study the impact of the surface of test arena on the mite behavior. We found that plastic from Petri dishes commonly used as test arenas disturbs the female mites and can cause death. We searched for a substrate that does not harm mites and found that gelatin-coated plastic Petri dishes responded to these expectations. We then investigated the host choice behavior of phoretic mites confronted with larval stages of the bee on gelatin-coated arenas to watch if the well-documented orientation towards 5th instar larva was observable in our conditions. Pupal stages were included in the host choice experiments, initially to act as neutral stimuli. As white-eyed pupae were revealed attractive to the mite, several pupal stages were then included in a series of host choice bioassays. These additional experiments tend to show that the positive response to the white-eyed pupa stage depends on cues only delivered by living pupae. Further investigation on the nature and impact of these cues are needed as they could shed light on key signals involved in the parasite lifecycle.