The Varroa mite, Varroa destructor, is considered the world’s greatest pest of honey bees. The mite is a natural pest of the Asian honey bee Apis cerana and it was not until European honey bees were introduced to Asia for propagation did this host shift occur with devastating consequences that has resulted in a near cosmopolitan distribution worldwide. Varroa was first detected in Hawaii in 2007 on Oahu and on Hawaii Island in 2008. Strict state laws prohibiting the movement of live bees and used beekeeping equipment between islands has thus far resulted in all neighboring islands remaining Varroa-free.

The ectoparasitic mite feeds on the fat tissues of larval and adult honey bees (Ramsey et al., 2019). The female mites are passed between adult worker bees as they pass one another inside the colony. Mites may be spread between colonies when foragers drift to different colonies within an apiary (a phenomenon known to increase when bees originate from heavily infested colonies), when bees from a healthy colony rob a weak colony, during swarming, and when beekeepers add bees from healthy colonies to supplement weak colonies. Migratory beekeeping practices may move mites to new areas within a region. To reproduce, the adult female will leave the adult bee and enter a brood cell just before it is sealed. This foundress mite will then feed on the developing pupa and lay an unfertilized male egg, followed by fertilized female eggs. She produces on average one offspring per worker cell and two offspring per drone cell. In warmer climates like Hawaii where brood are present year round, mite populations may increase 800-fold per year.

Varroa weaken and ultimately kill colonies by out-reproducing their hosts. Adult bee life spans are shortened in addition to the fact that the mites transmit multiple honey bee viruses, the most notable being Deformed Wing Virus (DWV). After the mites were introduced to Hawaii, feral colonies on Oahu and Hawaii Island decreased significantly. Consistent monitoring of managed colonies and immediate treatment of populations exceeding treatment thresholds are critical to minimizing colony losses associated with Varroa and the viruses they vector. Percent infestations of mites may be accurately quantified using an alcohol shake. When the number of mites per colony is in excess of 2-5%, it is recommended that colonies be treated. The Apiary Inspectors of America are considering lowering the recommended treatment threshold for Varroa to 1%. However, it appears that honey bee colonies in Hawaii are able to withstand slightly higher rates than on the mainland U.S. without experiencing widespread collapse, so the 3-5% treatment threshold should be sufficient for the foreseeable future. There are currently six registered organic products and three registered conventional products available for treating Varroa mites in Hawaii.

The most significant advancements in non-chemical control of Varroa has come from bee breeding programs. A number of hygienic and defensive responses have been selected for in natural and artificial breeding programs that include increases in removal of infected brood from the hive, increased grooming behaviors to remove mites from adult bees, and increased immunity to viruses vectored by the mite.

Since 2009, the number of Varroa per colony has seen a downward trend on Oahu, and on Hawaii Island since a spike in 2010. This decline is likely the result of access to educational information regarding treatment thresholds and the availability of treatment options in Hawaii. Since the decline of feral colonies on these two islands, reservoir populations have likely also decreased for reinfecting managed colonies. Hygienic bees have been introduced to apiaries on these islands, reducing the need for chemical treatments. However, the data generated by this survey likely underestimates the prevalence of Varroa as the surveyed apiaries are commercial, with Hawaii Island queen breeders required to maintain low Varroa levels for queens to qualify for export back to mainland North America. A needs assessment survey of beekeepers throughout the state revealed that many hobbyist and sideliner beekeeping operations choose not to monitor or treat for Varroa and thus are likely to have much higher infestation rates serving as reservoirs for neighboring colonies. Data are missing for 2017.

Nosemosis, or Nosema disease, is one of the most prevalent honey bee diseases worldwide, and is caused by a microsporidian parasite that lives within the cells of the honey bee gut. Adults honey bees become infected when they ingest spores from contaminated food and when cleaning infected fecal materials inside the hive. The chemical conditions inside the honey bee’s gut cause the spores to germinate, and the microsporidian replicates and spreads between cells, producing more spores. These spores are eventually expelled in feces and provide new sources of infection through cleaning and feeding activities within the colony. Two species have been identified in honey bees. N. apis levels of infection are highest in the spring with a smaller peak in the fall, while N. ceranae may increase in any season though spores are susceptible to chilling. For this reason, N. ceranae is believed to be more problematic in warmer climates such as Hawaii. N. ceranae is also the more pathogenic species, and it suppresses the honey bee immune system making them more susceptible to viral and other infections.

Infections are diagnosed by grinding up bee abdomens and microscopic observation of spores. Alternatively, spores may be observed microscopically in collected feces. More recently genetic techniques for identification have also become available. All adult colony members are susceptible to infection, including workers, drones, and queens. At the individual bee level, symptoms include structural changes to the hypopharyngeal glands in nurse bees effectively hindering the ability of those bees to feed developing larvae. This also induces rapid aging and infected bees only live half as long as healthy bees. Infected queens may or may not be able to continue laying eggs. At the colony level, nosemosis causes late winter and early spring reductions in adult workers, queen loss and/or supersedure, the presence of feces inside the hive in late fall and early winter due to an inability to defecate outside of the hive, and colony failure when adult death rates exceed bird rates. Together this reduces nectar collection and honey yields.

Despite the economic importance of this disease, it is often overlooked by beekeepers. This unfortunately means that infections are not diagnosed until symptoms are severe and available treatments will no longer be cost effective. Infected hive materials can be heated to 120°F for 24 hours to kill spores. Generic management practices that reduce Nosema levels include ensuring the colony has a strong queen going into fall, selecting apiary sites with good air flow, and ensuring colonies have supplemental feed during periods of nectar or pollen dearth.

In Hawaii, Nosema levels appear to cycle between years, with the different islands experiencing apparent cycles independent of one another. Spore counts are consistently higher than the national average on Hawaii Island, while Oahu apiaries are generally lower than the national average. Within years there is a high degree of variability in Nosema infections which may reflect differences in management strategies and microclimates on the islands. Data are missing for 2017.

Acute Bee Paralysis Virus (ABPV) belongs to the viral family Dicistroviridae and is closely related to IAPV and KBV. This virus is detected in both brood and adult bees, and commonly occurs in otherwise healthy bees. These inapparent infections may be maintained for generations within a honey bee population causing little or no harm. Within a colony, the virus is spread by salivary secretions of nurse bees to infected larvae. If sufficient viral particles are ingested, the larva will die before pupation. Otherwise, the infected larva will survive and emerge as an inapparently infected adult. ABPV is also transmitted by Varroa mites, and the presence of Varroa in an apiary may stimulate an inapparent infection to become lethal. This may be the result of digestive enzymes in the Varroa mite stimulating viral replication. However, ABPV is also detected in Varroa negative apiaries, indicating that transmission may occur independent of the mite. Infected adult bees exhibit shivering wings, darkened and hairless thoraces and abdomens, paralysis, and death outside the colony entrance. Adults die within one day.

With the exception of the most recent sampling year, the prevalence of ABPV in Hawaii has been greater than the national average. The virus has been recorded from all major islands, though the extent of the viral infection in apiaries does not appear to be strongly correlated with Varroa presence (Oahu and Big Island only). In the most recent sampling year, ABPV was only present on Oahu and Maui, with infection levels higher than the national average. Data are missing for 2015 and 2017.

As the name would suggest, Black Queen Cell Virus (BQCV) affects developing queens, though workers can be affected. Symptoms of BQCV include the queen pupa yellowing and developing a tough sac-like skin that rapidly darkens to dark brown or black, killing the developing queen and darkening the queen cell. The virus infects queen pupae during the capped-cell stage of development during spring and early summer. Outbreaks of this virus have been associated with Nosema infections, and bees with midguts infected with Nosema have an increased susceptibility to BQCV infection. Clinical symptoms in worker bees include drifting behavior and compromised orientation associated with higher viral titers (Retschnig et al., 2019).

For the two years during which BQCV was sampled, the virus was ubiquitous across the state on all major islands, though not all apiaries were infected. Due to the high rate of prevalence nationally, the NHBS coordinators stopped sampling after 2012 (Traynor et al., 2016). The highest rates of infection were reported from the Big Island, where the state’s major queen breeding operations are located.

Chronic Bee Paralysis Virus (CBPV) mainly affects adult honey bees and is characterized by two different types of “paralysis” symptoms. The more common form is characterized by abnormal trembling of the body and wings, crawling on the ground due to an inability to fly, bloated abdomens, and dislocated wings. The second form is characterized by the presence of hairless, shiny, and black-appearing bees. Both sets of symptoms may be observed in the same colony, with variations in symptoms reflecting inherited genetic differences to CBPV susceptibility. Unlike the Dicistroviridae viruses, CBPV infections are not associated with Varroa infestations but rather spread through bodily contact with infected bees, particularly in overcrowded colonies. Severe outbreaks are associated with environmental factors affecting normal foraging activities that create a nutritional dearth. This virus causes little economic impact to beekeepers, and requeening with resistant queens often helps eliminate disease symptoms.

CBPV was first detected in Hawaii in 2014 and thus far has only been recorded from the Big Island. The incidence of apiary infection is slightly below the national average and in 2018 the amount of virus per bee was lower in infected colonies than nationally. Data are missing for sampling years 2010, 2015, and 2017.

Honey bee worker symptomatic for CBPV. Photo by Randy Oliver, used with permission (https://bit.ly/2RSpwZ4).

Unlike other viral diseases in honey bees, Deformed Wing Virus (DWV, also referred to as DWV-A) causes easily recognizable symptoms in adults, including shrunken and crumpled wings, decreased body size, and discoloration in adults. It is transmitted during larval development by infected varroa mites, which are shown to be effective vectors of this virus. Ultimately, infected individuals die early as adults. Though the virus may also be detected in otherwise normal looking adult bees, viral loads in deformed bees are significantly greater and suggests that development of the deformity is dependent upon the viral dose present during the pupal stage. Colonies with symptomatic adults are often co-infected with high levels of varroa mites.

Three variants of this virus are known, DWV-A, DWV-B (also known as Varroa destructor virus-1, see below), and DWV-C. Prior to the detection of varroa mites in Hawaii in 2007, background levels of DWV were around 10% in colonies statewide. Since 2007-2008, the genetic diversity of DWV on varroa-positive islands has been eliminated, with a single highly virulent strain now present on Oahu and the Big Island (Martin et al., 2012).

In 2013, 2014, and 2016, DWV was only quantified from samples on Hawaii and Oahu islands. In 2018, DWV was also detected from colonies on Maui and Kauai, with the number of viral copies being similar to those recorded nationally. DWV was present on varroa-negative islands prior to 2018 (Martin et al., 2012) so the sudden detection is most likely the result of improved analytical techniques by the University of Maryland. However, the prevalence of DWV statewide since 2013 has remained lower than that reported nationally, likely due to the absence of Varroa destructor from Maui, Kauai, Molokai, and Lanai. Data are missing from Hawaii for 2015 and 2017 sampling years.

Israeli Acute Paralysis Virus (IAPV) was originally thought to be a honey bee-specific virus, but it is now known to have a wider host range, including solitary and social wild bees and social wasps. During the 2007 outbreak of Colony Collapse Disorder (CCD), IAPV presence showed a strong association with CCD which suggested that it may be a significant marker for this phenomenon. Infected adult bees exhibit shivering wings, darkened and hairless thoraces and abdomens, paralysis, and death outside the colony entrance. Symptoms are similar to those of ABPV and KBV, and IAPV shares high genetic similarity with these viruses, though distinct enough to represent a new species of virus in the viral family Dicistroviridae. IAPV may be transmitted vertically (from queen to offspring) or horizontally (from infected to uninfected individuals). The virus has also been found in pollen stores and bee feces, and can be transmitted by varroa mites (Chen et al., 2014).

This virus was not detected in Hawaii until 2012. To date IAPV has only been detected on Oahu and the Big Island, with a statewide prevalence slightly lower than what is reported nationally. The severity of infection, as measured by the number of viral copies per bee, was slightly higher on the Big Island than the national average in 2018. Data are missing from Hawaii for the 2015 and 2017 sampling years.

Symptoms of Kashmir Bee Virus (KBV) are similar to those of ABPV and IAPV (shivering wings, darkened and hairless thoraces and abdomens, paralysis). This virus is incredibly virulent in laboratory settings and can cause mortality within three days. KBV persists as an inapparent infection in brood and adults with lethal levels of infection triggered by additional stressors such as parasitic mites and other pathogens. Varroa mites are shown to vector KBV between infected and healthy honey bees, as well as to other uninfected mites cohabiting the same brood cell.

This virus is relatively uncommon in Hawaiian apiaries. In years where it has been detected, the statewide prevalence is similar to the national prevalence. KBV was absent from all sampled colonies in 2010 and 2018. Data are missing for 2011, 2015, and 2017.

The Lake Sinai group of viruses was first described from honey bee colonies in South Dakota in 2011 and has since been identified from surveys worldwide. Lake Sinai Virus-2 (LSV2) represents one of the more common, related clusters of these viruses. LSV2 is present in both healthy and weak colonies, though viral loads are higher in weaker colonies. Viral levels are highest in gut tissues, suggesting that a food mediated or fecal-oral route of transmission is likely (Daughenbaugh et al., 2015). LSV2 is also found in varroa mites, indicating that transmission may be vector mediated. Symptoms for these viruses are not described.

LSV2 was first detected in Hawaii in 2014 on Lanai, and from Maui in 2016. In the most recent sampling year, this virus was also detected from the Big Island, Oahu, and Kauai, with a statewide prevalence approaching that nationally, though the severity of infection in Hawaii is two orders of magnitude lower than the national average. Data from 2015 and 2017 are missing.

Varroa Destructor Virus (VDV-1) is a DWV-like virus, and may also be referred to as DWV-B. Along with DWV, this is one of the two most prevalent honey bee viruses. It is vectored by Varroa mites which has led to the selection of particularly virulent strains. The NHBS first started testing for this virus in 2016, where it was detected in Big Island apiaries. By 2018, it was also found on Oahu, Maui, and Kauai, with viral loads being greater in Hawaii than nationally, though the proportion of apiaries testing positive is similar to that nationally. Data are missing for 2017.

A complete pesticides analysis panel was run for beeswax samples collected from five apiaries across the state in 2018, and included testing for 193 pesticides and their metabolites in each wax sample by the USDA Agriculture Marketing Service. Aged wax was collected from inside each of eight colonies sampled from the five apiaries, and analysis conducted on combined wax samples. Thus, results are reported at the apiary level. A statewide summary is provided here to protect the identity of participating beekeepers.

Nationwide, wax samples analyzed in 2018 contained between one and 38 pesticides, with a median of 11 pesticides detected per apiary. Apiaries in Hawaii contained fewer pesticides, with a median of six pesticides detected per apiary (average of seven pesticides per apiary), and only 22 of the 193 tested compounds were detected in the state. 20% of detected pesticides were varroacides, 20% were herbicides, 26% were insecticides, and 34% were fungicides, which is consistent with the breakdown for the rest of the country (28% varroacides, 12% herbicides, 21% insecticides, 38% fungicides). The table below provides a description of the pesticides detected in Hawaiian beeswax. Concentrations were almost always much lower than the national average. Two pesticides (Diphenylamine and Fluometuron) were detected in multiple samples across the state, despite there being no commercial products containing these chemicals registered for use in Hawaii.

¹Pesticide not currently registered for use in Hawaii.

²LOD = limit of detection. A pesticide may be present below this threshold, but cannot be quantified and is thus categorized as “trace.”

³n refers to the number of apiaries testing positive.