In recent years, beekeepers have had to confront numerous challenges including diseases, pests, parasites, predators, and climatic factors. Among these, Acute Bee Paralysis Virus (ABPV) stands out as a major threat to apiculture worldwide. It was first identified during laboratory research focusing on the agent behind bee paralysis, originally linked to the Chronic Bee Paralysis Virus (CBPV).
Like many honey bee illnesses, ABPV can easily spread between colonies and hives due to bees’ social behavior during foraging. Human activities—including hive inspections, transporting bees for pollination, importing bees, and poor hygiene practices—also contribute to the transmission of these diseases.
Differences between the Acute and Chronic Bee Paralysis Viruses
Although Acute Bee Paralysis Virus exhibits symptoms similar to CBPV, the term ‘acute’ highlights a higher mortality rate among infected bees. A key distinction is that ABPV’s virulence is closely linked to Varroa mite infestation. The virus is typically spread by mature, asymptomatic bees through larval jelly to developing larvae and via Varroa mites to larvae and pupae. ABPV causes infected bees to die earlier compared to those with CBPV.
Additional distinctions between ABPV and CBPV include the following:
- ABPV can infect bees without producing clear symptoms.
- ABPV’s spread accelerates when Varroa mites feed for longer periods.
- Infected pupae die before emerging from brood cells, making ABPV difficult to detect and ultimately leading to reduced colony populations and potential collapse.
- Honey bee colonies can be decimated by ABPV within a single season, in contrast to the slower progression seen with CBPV.
Prevalence of the Acute Bee Paralysis Virus
ABPV is found worldwide, with confirmed cases across the United States, Africa, Asia, Europe, and the Middle East. It belongs to the Dicistroviridae family and is so widespread among bee populations that complete eradication is virtually unachievable.
Acute Bee Paralysis Virus and the Varroa Destructor
Varroa destructor mites are the primary vectors of ABPV, and the virus is a major factor in colony losses, especially when these mites infest hives. Adult bees infected with ABPV transmit the virus through salivary secretions as they feed larvae; the virus may also be present in pollen, infecting young bees. Larvae that ingest high viral loads typically perish before their brood cells are capped, while some may survive to adulthood uninfected.
ABPV can persist latently inside bee cells and may become active if bees are parasitized by Varroa mites or when the virus is released from cellular reservoirs. Once activated, it spreads throughout the bee’s body, potentially killing adults and infecting brood. Infected larvae often die within the cells before capping. There is currently no specific treatment for ABPV; however, managing other diseases and especially keeping Varroa mite levels low is critical.
ABPV is common and infects many honey bee colonies, including those considered healthy. However, colony collapse incidents frequently coincide with the presence of ABPV alongside Varroa mite infestation. Varroa mites play a pivotal role in disseminating various viruses throughout colonies and exacerbate infection severity.
The Varroa mite likely serves as a vector for ABPV, weakening honey bees and intensifying viral infections that cause clinical symptoms and colony losses. Studies in the UK have shown that ABPV is responsible for significant declines and deaths in many hives, particularly those heavily infested with Varroa mites.
Varroa mites trigger serious infections in honey bees, many of which are difficult to detect. Environmental factors such as pollution, excessive chemical and insecticide use in agriculture, and associated stress further increase bees’ susceptibility. Some acaricides used against Varroa mites may inadvertently weaken bees’ immune systems, making them more prone to other diseases. Given the ongoing decline of natural pollinators due to pollution, honey bees have become increasingly vital for crop and plant pollination, underscoring the importance of preserving their health beyond just honey production.
Symptoms of the Acute Bee Paralysis Virus
Honey bees affected by ABPV exhibit a spectrum of signs, ranging from no visible symptoms to rapid death within hours.
- One early symptom is a swollen abdomen caused by accumulation of fluid in the honey sac.
- Infected bees also display weak, trembling wings and tend to crawl around the hive entrance because their impaired wings prevent them from flying.
- Other indicators include hair loss on the abdomen and a dark, greasy appearance. As flight capability diminishes, the bees lose strength and eventually succumb to the infection.
Sometimes, honey bees carry the disease without displaying any symptoms, making it impossible to detect before their death. This asymptomatic infection poses a significant risk as these bees can spread the virus beyond their own hive undetected.
Researchers observed dead brood, both sealed and unsealed, during tests for Acute Bee Paralysis Virus, complicating diagnosis based on symptoms alone. The absence of bacterial presence further hindered identification of the virus. Studies conducted in Germany and the Netherlands revealed a strong link between ABPV presence and high varroa mite infestations. Additionally, adult bee populations sharply declined during peak ABPV outbreaks, especially in late summer.
Tests on uninfected British bee colonies found no ABPV in samples from dead bees, indicating that ABPV likely causes the increased mortality seen in infested colonies across Europe and beyond. This suggests that the virus exacerbates problems in colonies already affected by varroa mite infestations.
Laboratory investigations have demonstrated that adult female varroa destructor mites transfer ABPV to healthy honey bee pupae. These experiments also revealed that mites remain capable of transmitting the virus up to 36 hours after detaching from an infected bee and can infect multiple hosts in succession.
Although there is no evidence that ABPV replicates within varroa mites, transmission is effective because mites ingest the virus along with the haemolymph of infected bees. The virus accumulates in the mites’ digestive tract and may be transmitted to new hosts through regurgitation during feeding, a mechanism similar to that seen in some plant virus vectors carried by beetles.
Infection of honey bees can occur with a very small viral load—around 100 particles injected into the haemolymph are sufficient. Remarkably, female mites collected from naturally infected colonies can carry viral quantities nearly a million times greater than this infectious dose.
The virus passes harmlessly through the varroa mite’s digestive system, yet even a minor amount introduced into the haemolymph of other bees or pupae during feeding can start new infections. Large populations of V. destructor along with viral pathogens contribute to the spread of ABPV, potentially leading to colony collapse.
ABPV is highly contagious and spreads faster than infected honey bees perish. The virus load within a colony can increase significantly due to contact and food exchange among bees, facilitating the virus’s introduction and proliferation.
Routes of Transmission
Acute Bee Paralysis Virus spreads easily both within and between honey bee colonies, and it can also infect other local bees and insects. Transmission occurs in various ways: during mating from drone to queen, from queen to eggs, from nurse bees to larvae while feeding, and between workers through trophallaxis. Environmental exposure also plays a role, with bees acquiring the virus from contaminated food sources such as hive-stored honey or infected flowers.
Diagnosis of the Acute Bee Paralysis Virus
Confirming ABPV infection requires laboratory analysis involving sophisticated examination of the virus’s genome. This pathogen, which has severely impacted apiaries worldwide, threatens honey bee survival significantly. One key target gene in testing is the capsid polyprotein gene. Diagnostic efforts have been conducted in countries like the United States, Austria, Hungary, Germany, and notably in the UK, which has been a leader in ABPV detection.
Laboratory results have consistently verified the presence of ABPV. Scientists classify it not under a specific virus genus but as part of the picornavirus family, a group known for affecting insects and including viruses termed cricket paralysis viruses. ABPV shares antigenic characteristics and genetic sequences closely resembling those of the Kashmir bee virus.
Managing Viral Infections
Currently, there is no specific treatment for Acute Bee Paralysis Virus, limiting options for combating the disease. Nonetheless, beekeepers can adopt various strategies to reduce virus spread and limit interactions with triggers such as parasites, pesticides, and poor nutrition. Effective management depends on thoroughly understanding the biological mechanisms behind the virus’s interactions.
Integrated Pest Management (IPM) programs offer an effective framework for controlling ABPV by minimizing reliance on hazardous pesticides. IPM incorporates developing economic thresholds, breeding bees with genetic tolerance, implementing cultural practices that disrupt parasite life cycles, enhancing social immune responses, and using semiochemicals to trap or inhibit pest mating. This holistic approach helps delay pest population growth and reduces chemical pesticide use.
When pest levels reach economic thresholds, highly toxic pesticides should be rotated and applied only according to legal guidelines, preventing resistance by avoiding successive use of the same active ingredients. Benefits of IPM in combating pests and diseases include lowering pesticide residues in hive products and the environment, reducing beekeeper exposure to toxins, extending pesticide efficacy, improving queen and drone reproductive success, and fostering faster colony growth and productivity.
1. Cultural Solutions
Utilize bee strains that demonstrate resistance to Varroa mites, such as Russian stock, Varroa-sensitive strains, and leg-chewer or ankle-biter types. These breeds have been proven effective at controlling viral levels within their colonies.
2. Reduce Transmission within and Between Colonies
ABPV spreads readily both within individual colonies and between separate ones, especially when many colonies are densely packed. Smaller colonies tend to be less susceptible compared to larger, crowded hives.
Beekeepers can adopt several practices to minimize virus transmission, including:
- Keeping fewer colonies in each apiary to reduce the chance of ABPV and other viruses spreading among dense bee populations.
- Arranging hives to decrease drifting of infected bees by spacing colonies widely, orienting them in varied directions, and marking them differently.
- Avoiding transferring frames from colonies exhibiting ABPV symptoms into healthy ones.
- Disinfecting hive tools and other equipment with alcoholic solutions after inspections and immediately upon recognizing infection symptoms.
- Ensuring proper nutrition for honey bees, especially when providing supplemental feeding, is crucial. Bees should be given high-quality food sources, and it’s important to assess whether nearby forage areas offer adequate nutrition during different seasons such as spring, summer, or fall. If bees consistently avoid certain areas, it can indicate poor forage quality. In such cases, supplementing their diet becomes necessary. Ideally, apiaries should be situated close to rich forage zones, since research shows that naturally collected pollen is generally superior in promoting bee health compared to supplements. Another approach is to collect pollen from robust colonies using pollen traps and store it frozen for later use.
3. Reduce Exposure to Pesticides
Beekeepers should register with local authorities to receive notifications about upcoming pesticide applications in their area. Building good communication with local farmers can also be beneficial, as various guidelines are available to facilitate discussions regarding pesticide use, helping minimize bee exposure.
4. Mechanical Approaches
Old Comb Replacement
Regular rotation of old combs is essential to remove accumulated viruses and contaminants. Replacing approximately one-third of the frames in each colony annually helps maintain hive health. All outdated combs should be discarded and destroyed to prevent disease buildup.
Propolis Accumulation
Encouraging bees to deposit propolis inside the hive strengthens their defenses. Rough inner surfaces of hive equipment stimulate bees to fill gaps with propolis. Using rough wood or intentionally scratched inner surfaces can promote this behavior. Additionally, lining the inner cover with cotton duck cloth encourages propolis collection. Propolis not only enhances immune gene expression in bees but also helps reduce virus levels within colonies.
5. Chemical Interventions
Currently, no commercial chemical treatments exist specifically targeting Acute Bee Paralysis Virus. However, certain naturally derived substances, often not commercially available, may help lower viral loads. These include:
Thymol Treatment
Applying 0.16 ppm thymol to emerging honey bees before returning them to the hive can reduce ABPV levels. Nevertheless, results have been inconsistent, indicating a need for further research to validate its effectiveness.
Propolis and Fungal Extract Applications
Reducing ABPV can also be achieved by treating the interior surfaces of beehives with solutions containing propolis or fungal extracts. These treatments inhibit viral spread. Bees naturally use propolis to coat hive interiors and entrances, where it serves multiple roles: deterring large intruders, insulating, and disinfecting bees as they enter the colony.
Summary
As with many viral infections, Acute Bee Paralysis Virus lacks direct medicinal cures. Addressing underlying factors may help alleviate viral infections tied to other pathogens or conditions. Tackling the causes of bee deaths related to ABPV requires the development of standardized diagnostic methods, regional data collection to track disease trends, and educational programs that enhance beekeeper detection skills locally. Given the significant economic risks these viruses pose to beekeeping, eliminating factors that exacerbate losses and contribute to severe bee mortality is vital. Formulating an effective control strategy depends on accurate diagnosis and ruling out other causes in every case.