Contact Effect Contribution to the High Efficiency of Lithium Chloride Against the Mite Parasite of the Honey Bee

Deleterious effect of LiCl on honeybee (Aphis mellifera) grubs and no effect on Varroa mites (Varroa destructor) under normal beekeeping management

A 2-year field experiment was performed to test lithium chloride, LiCl, application in a normal beekeeping management system. The effect of LiCl on bee larval mortality, beehive weight (honey production) and Varroa mite mortality were tested. Spectrometric quantification of Li on honey and the larval body were made to test the effectiveness of the presence of LiCl. Li was detected in bee larval bodies and in honey over 2 years, from 2018 to 2019. According to the results, no effect of LiCl on mite mortality or bee larval mortality was detected in the first year of application. By assessing the weight variation of beehives, only one LiCl-treated hive showed a significantly higher weight, whereas no other differences were detected between treatments and control. The same trend seen in 2018 was repeated in 2019, while a total bee larval mortality was observed after the first LiCl application, and still no differences in Varroa mite mortality were observed. According to these results, it was concluded that LiCl has no effect on Varroa mite mortality during normal beekeeping practice; furthermore, the recommended amount of treatment (25 mM) had a lethal effect (i.e., total mortality) on larvae following repeated applications.

Lithium chloride treatments in free flying honey bee colonies: efficacy, brood survival, and within-colony distribution

The efficacy of various lithium chloride (LiCl) applications in eradicating the parasitic mite Varroa destructor in honey bee colonies was investigated, with a specific focus on its impact on brood development. In broodless colonies (3 weeks post queen caging), the highest efficacy of 98% was achieved with a 9-day treatment of 2.5 kg of candy spiked with 50 mM LiCl. A shorter 5-day treatment with 2 kg of 50 mM LiCl candy resulted in an efficacy of 78%. In colonies with brood, a repeated short-term application of 4 × 0.5 kg 50 mM LiCl candy yielded an efficacy of 88%. LiCl treatment led to a removal of the first batch of brood reared after release of the queen. However, no long-term effects on colony growth were observed, and the colonies successfully overwintered. Additionally, the study demonstrated that lithium is rapidly distributed among the bees of a colony within 2 days, yet only low concentrations were detected in stored food samples. This suggests that the bees efficiently absorb and distribute lithium within the colony. The harvested honey in the following spring revealed a lithium concentration of 0.1-0.2 mg/kg, which is below naturally occurring lithium levels in honey. Based on these findings, LiCl can be considered an effective and easy-to-apply acaricide in broodless colonies, and even in colonies with brood, it had good efficacy and no long-term effects on colony survival. Further research may be necessary to determine the optimal treatment period for achieving an efficacy over 95%.

Efficacy of In Vitro Lithium Chloride Treatments on Dermacentor reticulatus

Dermacentor reticulatus (Fabr., 1794) (Acari: Ixodidae) is parasite that spreads many diseases which are dangerous to humans and animals. Microelement lithium was found to have promising potential against the detrimental bee pest Varroa destructor. Furthermore, its effectiveness was confirmed against Dermanyssus gallinae, a major parasite of poultry, in vitro. In the present study, we investigated whether the efficacy of lithium chloride extends to other parasitic species, such as D. reticulatus. Our results revealed, for the first time, that the effectiveness of lithium chloride extends to D. reticulatus, confirmed to have 100% mortality at a relatively high minimum concentration of 1.38 M in vitro. The 24 h and 48 h median lethal concentration (LC₅₀) values proved to be 0.654 M and 0.481 M, respectively, for this species. Our pilot study may contribute to a better understanding of the properties of lithium ion. Furthermore, it may elicit further studies aiming to reveal whether the different environmental mineral conditions may influence the D. reticulatus population. Further studies might reveal whether lithium has any possible veterinary relevance.

Lithium Chloride Shows Effectiveness against the Poultry Red Mite (Dermanyssus gallinae)

The poultry red mite (Dermanyssus gallinae) is the main pest of poultry, causing severe problems by being a vector of several animal and human pathogens. The number of miticides is few, and their efficacy in practice implies problems of residues and resistance; therefore, the demand for a new and safe agent is constant. The present publication investigated the effectiveness of lithium chloride under in vitro conditions on poultry red mites. This chemical currently appears to be one of the most promising alternatives to study amongst potential applicants to treat varroosis, a fatal disease of honey bees. In Experiment I, the previously used experimental doses (5.52 M, 2.76 M, 1.38 M) on Varroa mites confirmed their in vitro activity on the poultry red mite. Three event times (uncontrolled movement, immobilisation and death) were recorded to base the response to treatment for each concentration. In Experiment II, the LD 50 value was calculated, i.e., the value at which 50% of the mites were killed by the treatment. This Experiment showed that the LD50 of lithium chloride = 0.265 M in the poultry red mite. It is to note that the study remained restricted to in vitro confirmation of lithium chloride's effectiveness on the parasite. Thus, further extensive studies are needed to decide whether it has any relevance in practice against D. gallinae, and also to assess potential residue problems that could affect poultry products.

Lithium salts: assessment of their chronic and acute toxicities to honey bees and their anti-Varroa field efficacy

BACKGROUND

Varroa control is essential for the maintenance of healthy honey bee colonies. Overuse of acaricides has led to the evolution of resistance to those substances. Studies of the short-term acaricidal effects and safety of various lithium (Li) salts recently have been reported. This study examined the long-term in vitro and in vivo bee toxicities, short-term motor toxicity to bees and long-term anti-Varroa field efficacy of several Li salts.

RESULTS

In an in vitro chronic-toxicity assay, lithium citrate (18.8 mm) was the most toxic of the examined salts, followed by lithium lactate (29.5 mm), and lithium formate (32.5 mm). In terms of acute locomotor toxicity to bees, all of the Li salts were well-tolerated and none of the treatment groups differed from the negative control group. In an in vitro survival study, all of the Li treatments significantly reduced bee life spans by a factor of 1.8-7.2, as compared to the control. In terms of life expectancy, lithium citrate was the most toxic salt, with no significant differences noted between lithium formate and lithium lactate. In the bee-mortality field study, none of the examined treatments differed from the negative control. Amitraz and lithium formate exhibited similar acaricide effects, which were significantly different from those observed for lithium lactate and the negative control.

CONCLUSION

In light of lithium formate's honey bee safety and efficacy as an acaricide, additional sublethal toxicity studies in brood, drones and queens, as well as tests aimed at the optimization of administration frequency are warranted. © 2022 Society of Chemical Industry.

Contact varroacidal efficacy of lithium citrate and its influence on viral loads, immune parameters and oxidative stress of honey bees in a field experiment

With an almost global distribution, Varroa destuctor is the leading cause of weakening and loss of honey bee colonies. New substances are constantly being tested in order to find those that will exhibit high anti-Varroa efficacy at low doses/concentrations, without unwanted effects on bees. Lithium (Li) salts stood out as candidates based on previous research. The aims of this study were to evaluate Li citrate hydrate (Li-cit) for its contact efficacy against Varroa, but also the effect of Li-cit on honey bees by estimating loads of honey bee viruses, expression levels of immune-related genes and genes for antioxidative enzymes and oxidative stress parameters on two sampling occasions, before the treatment and after the treatment. Our experiment was performed on four groups, each consisting of seven colonies. Two groups were treated with the test compound, one receiving 5 mM and the other 10 mM of Li-cit; the third received oxalic acid treatment (OA group) and served as positive control, and the fourth was negative control (C group), treated with 50% w/v pure sucrose-water syrup. Single trickling treatment was applied in all groups. Both tested concentrations of Li-cit, 5 and 10 mM, expressed high varroacidal efficacy, 96.85% and 96.80%, respectively. Load of Chronic Bee Paralysis Virus significantly decreased (p < 0.01) after the treatment in group treated with 5 mM of Li-cit. In OA group, loads of Acute Bee Paralysis Virus and Deformed Wing Virus significantly (p < 0.05) increased, and in C group, loads of all viruses significantly (p < 0.01 or p < 0.001) increased. Transcript levels of genes for abaecin, apidaecin, defensin and vitellogenin were significantly higher (p < 0.05—p < 0.001), while all oxidative stress parameters were significantly lower (p < 0.05—p < 0.001) after the treatment in both groups treated with Li-cit. All presented results along with easy application indicate benefits of topical Li-cit treatment and complete the mosaic of evidence on the advantages of this salt in the control of Varroa.

Comparison of Alternative Application Methods for Anti-Varroa Lithium Chloride Treatments

Varroosis is one of the most dangerous threats to the bee industry but means of its treatment are still unsatisfactory. Lithium-based anti-Varroa treatments may provide an alternative, as this trace element can be a natural component of honey and is well tolerated by adult bees. However, it can be toxic to larvae and its use in beekeeping practice is not yet well understood. The present study aimed to investigate the efficacy of relevant application methods of acaricides used in beekeeping practice in brood-free conditions for lithium. Vaporisation proved to be an inefficient method of lithium treatment and killed only 9.9 ± 3.3% (mean ± SD) of mites in the hive. Lithium-impregnated paper strips showed moderate efficiency by killing 55.1 ± 26.2% of mites. The most effective way of applying lithium was the trickling method; different trickling treatments decreased the abundance of mites on average by 65 to 99.7%, depending on the applied dosage and the number of treatments. Repeated trickling treatments were more effective than single treatments, and they generally provided >90% efficiency. Experiments also proved that adding sugar to the trickling solution does not influence treatment efficiency. Thus, it is suggested that repeated and sugar-free trickling treatments with moderate lithium dosage could be the most rational methodology. Since lithium is not yet legalised in beekeeping practice, comprehensive studies are also needed to uncover the amount of lithium residue in bee products, depending on the treatment parameters.

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.

Changes in Lithium Levels in Bees and Their Products Following Anti-Varroa Treatment

Simple Summary

Varroosis caused by the ectoparasitic mite Varroa destructor has been the biggest threat to managed bee colonies over recent decades. Chemicals available to treat the disease imply problems of resistance, inconsistent efficacy, and residues in bee products. Recently, alongside novel compounds to defeat the pest, lithium chloride has been found to be effective. In this study, we found that lithium treatments leave beeswax residue-free. The possibility of decontamination in adult bees, bee bread, and uncapped honey was revealed. On the other hand, ripe honey was found to be affected by lithium administered via feeding. Case studies are necessary to uncover the level of exposition in harvested honey to estimate its potential risk once it becomes a registered veterinary medicine.

Abstract

The biggest threat to beekeeping is varroosis caused by the mite Varroa destructor. Chemicals available to treat this fatal disease may present problems of resistance or inconsistent efficacy. Recently, lithium chloride has appeared as a potential alternative. To date, the amount of residue lithium treatments may leave in honeybee products is poorly understood. Honeybees were fed with 25 mM lithiated sugar syrup, which was used in earlier studies. The accumulation and elimination of the lithium were monitored in bees and their products for 22 days. Lithium concentration increased in the entire body of the bees to day 4 post-treatment and then recovered rapidly to the control level. Lithium exposure was found to affect uncapped honey in the short term (<16 days), but ripe (capped) honey measured at the end of the trial remained affected. On the other hand, lithium treatment left beeswax lithium-free. Based on these data, we propose that comprehensive research on harvested honey is needed to decide on the veterinary use of lithium.

Lithium chloride outperformed oxalic acid sublimation in a preliminary experiment for Varroa mite control in pre-wintering honey bee colonies

Since lithium salts were demonstrated to be very effective for the potential control of Varroa destructor, a highly detrimental parasite of honey bee (Apis mellifera), no studies have been reported on their comparison with any commonly used varroicides in commercial bee colonies. In this study we compared the effectiveness of lithium chloride to that of oxalic acid, a widely used miticide. The results of the present study confirm that lithium has superior efficacy to oxalic acid sublimation both as a main or a supplementary pre-wintering treatment at moderate infestation levels, restricted to certain pre-wintering conditions. Considering its easy implementation in apicultural practice and its twofold mode of action, trickling would be the preferred way of administration after the use of lithium salts as varroicides is authorised.

An Alternative, High Throughput Method to Identify Csd Alleles of the Honey Bee

Applying instrumental insemination in closely related honey bee colonies often leads to frequent lethality of offspring causing colony collapse. This is due to the peculiarities of honey bee reproductive biology, where the complementary sex determination (csd) gene drives sex determination within a haplodiploid system. Diploid drones containing homozygous genotypes are lethal. Tracking of csd alleles using molecular markers prevents this unwanted event in closed breeding programs. Our approach described here is based on high throughput sequencing (HTS) that provides more data than traditional molecular techniques and is capable of analysing sources containing multiple alleles, including diploid individuals as the bee queen. The approach combines HTS technique and clipping wings as a minimally invasive method to detect the complementary sex determiner (csd) alleles directly from honey bee queens. Furthermore, it might also be suitable for screening alleles of honey harvested from hives of a closed breeding facility. Data on alleles of the csd gene from different honey bee subspecies are provided. It might contribute to future databases that could potentially be used to track the origin of honey. With the help of tracking csd alleles, more focused crossings will be possible, which could in turn accelerate honey bee breeding programmes targeting increase tolerance against varroosis as well.