The honey bee pesticide mystery

Honeybee Mystery/Pesticides

HoneyBee Mystery

The mystery of the honeybees vanishing remains a largely unsolved puzzle. Thus far, no single cause has been established for the Colony collapse disorder and scientists are beginning to approach the problem as a multifactorial symptom. The indiscriminate and systemic use of pesticides threatens to destroy the keystone species -- the honeybee that drives our agricultural economy. Adoption of integrated pest management system is indispensable in our efforts to revive the honeybee populations once again while at the same time limiting the damage caused by the pests below economic injury levels. The onus rests with us to protect this vital insect species that plays a major role in supporting our lives.

Introduction

The new millennium has given us new problems to solve. Climate change, global warming, artic meltdown are just a few starring environmental concerns. However, over the last few years, a new and equally important problem has arisen in the United States. It is the sudden and mysterious disappearance of the Honeybees. As insignificant as it may seem, yet the vanishing honeybees present a huge crisis, one that could have a significant impact on the entire agricultural economy of our nation. Going by the USDA report, bees contribute around $15 billion per year to the nations agricultural economy and are involved in the pollination of more than 130 crop varieties. [Dan Kulpinski] Speculation on the disappearance of honeybees has ranged from parasites infestation to virus attack to pesticide usage and even stress factors. While scientists are still speculating the actual cause or the possibility of several related factors, the crisis situation has prompted agriculturists and entomologists to look at methods that could reverse the situation. A brief overview of the problem is discussed with the potential causative factors and the possible solution for the crisis.

Colony Collapse Disorder

Colony collapse disorder is a term now familiar among beekeepers across the nation. CCD in essence means that adult worker bees deserting the honey filled beehives leaving no clue as to their whereabouts. With no dead bees around the hive, this strange phenomenon of the worker bees is threatening the entire agricultural scenario of the U.S. First reported in 2006 in the U.S., researchers are still unable to pinpoint the exact cause of such strange bee behavior. As per a recent survey conducted by the national agricultural research service, beekeepers around the country have reported a loss of 37% of their colonies in the year 2007. This is a shocking development and wake up call for agriculturists and environmental researchers. As the U.S. agricultural Committee recently reported, 'The syndrome is mysterious in that the main symptom is simply a low number of adult bees in the hive. There are no bodies, and although there are often many disease organisms present, no outward signs of disease, pests, or parasites exist' [Benjamin P. Oldroyd, 2007]

Loss of colonies in itself is not a new problem. Loss of bee colonies have been documented and the most recent of which was the 1995 Pennsylvania case where beekeepers reported a loss of around 53% of their colonies. Bee population tends to have a natural fluctuation year by year but what is alarming now is the reports of CCD across the entire stretch of America and some parts of Europe with some of the beekeepers reporting the loss of around 80-100% of their colonies. [Benjamin P. Oldroyd, 2007] In solving the mystery of this sudden CCD among the honey bees, researchers have focused on every possible contributing factor including parasites, viruses, pesticides and the vastly changed and commercialized cultural practices and their impact on the bee behavior. A discussion of these various potential causes would shed more light into the issue.

Parasite Infestation

It is well-known that the chief pest that attacks honeybees is the Varroa destructor, a phoretic parasite, which lives on adult bees. Studies have shown that the Varroa destructor can pass on the deadly deformed wing virus (DWV) to the honeybees resulting in the development of crippled wings. Study has shown that the viral load of the infested mite has a direct bearing on severeness of the symptoms and at lower loads, the DWV is well tolerated and the honeybees remain non-symptomatic. [Sebastian Gisder, 2009] However, acute mite infestation is very obvious for the beekeepers and it does not explain the sudden CCD. There are reasons to suspect that infestations from the other parasite Acarapis woodi or tracheal mite, which is very widespread in the U.S., may be one of the chief causes for the CCD.

Viral Infections

Honeybees are susceptible to a variety of viral infections but in most cases they remain symptom free. But research has shown that under unfavorable conditions involving greater stress, parasitic infection, environmental or nutritional imbalance, these viral infections become more potent and fatal. One of the main Symptoms of the DWV infection is severe trembling.

Researchers opine that the absence of distressed trembling worker bees would exclude the paralysis virus infection as a cause of the recent CCD observed throughout the nation. However, a recent German study by Iqbal and Mueller has reported that infection by the DWV could cause expression of symptoms other than trembling and shaking that are usually noticed. Their study found that DWV infections interfere with the associative learning and impair memory in Apis mellifera. Associative memory is very critical for honeybees and any effect on the associative memory can block their normal foraging behavior. [Javaid Iqbal, 2007]

Recently, the focus has shifted on a new virus known as the Israeli Acute Paralysis Virus (IAPV). Studies have shown that the virus came from the infected Australian bees that were imported to the U.S.A. In 2005 due to the mounting pressure from the almond growers association. Since almonds solely depend on bees for their pollination, the lack of enough bees forced the U.S. government to lift its 1992 embargo on bee imports. A recent study by Cox-foster identified the IAPV as a clear marker in the samples from the CCD affected migratory bee operations. Further, confirming evidence came in the form of IAPV infected cockroaches, which had infested the CCD affected beehives. The researchers conducted more tests by infecting German cockroaches with infectious fluids obtained from the affected bees. The cockroaches started to die within 4 days and analysis of the dead cockroaches enabled the researchers to obtain the IAPV virus but not other viruses. As Mr. W. Ian Lipkin from the Colombian university, who did most of the genome sequencing part for this research says,' This clearly proves that the virus is capable of causing disease in insects. But we don't know if it's [IAPV] necessary or if it's sufficient" to cause CCD., " [Myrna E. Watanabe, 2008] Scientists view that the bees weakened by the varroa mite attack maybe more susceptible to other pathogens like the IAPV.

However, as mentioned earlier the virulence of viruses is an important factor. Even healthy bee populations such as the Australian bees are infected with IAPV without any symptoms. To further investigate the role of IAPV, Cox-foster and colleagues administered infectious preparations from the CCD affected bees to healthy Hawaiian bees. Cox-foster reported, "We are beginning to see some mortality in the colonies," [Myrna E. Watanabe, 2008] The researchers are hoping that further sequencing of the genetic material of the Hawaiian bees would offer more evidence in this direction.

Environmental Insults (a potential cause)

As the mystery of the honeybee disappearance continues to baffle us, agriculturists and entomologists are seriously considering the role of environmental pollutants in the form of pesticides and their various metabolites as the causative factors. Research has focused on both in hive chemicals and agricultural pesticides including the bio pesticides in genetically modified crops. Christopher Mullin, professor of insect toxicology at Penn state university, and a team of researchers are studying for evidence of pesticide metabolites in a variety of samples such as pollens, wax, nectar and the bees. "We're seeing a lot of chemicals, a lot of residues. "We're still trying to understand it." [Myrna E. Watanabe, 2008]

In the commercial beehives, pesticides are used to control parasites such as the V. destructor and hive beetle (A. tumida ). However, the V. destructor mite has acquired resistance against the widely used pesticide 'pyrethroid fluvalinate' which led to the switchover to organophosphate coumophos. However, in 2001, a commercial beekeeper from Maine complained that the use of (Checkmite +), a formulation of coumophos did not check the growth of V. destructor. To detect possible development of resistance, researchers conducted assays on bee colonies in Maine, Florida and Maryland using Checkmite+ strips. The study results showed a higher mortality rate for mites in the Maryland colonies (80-100%) which had been exposed to checkmite+ for only one season prior to the study when compared to Maine population (13%) and Florida population (7 to 80%). This clearly indicated the development of resistance to coumophos among the Maine and Florida mites. [Pettis J.S, 2003] This led to the use of a new chemical compound knows as Amitraz, a triazapentadiene, whose effects have not yet been fully understood. Some beekeepers use a combination of pesticides. Studies have confirmed traces of fluvalinate concentrations in honey and wax samples obtained from colonies that were treated with two strips of Apistan. [Gatien, 2003]

Besides these In-hive chemicals, bees are also affected by the agricultural pesticides when they feed on the pollens. Though these pesticides undergo a rigorous testing phase before they are made commercially available, the risk factors for Non-target ecosystems are not always fully understood. With newer pesticides appearing on the market to replace older ones, which have become less effective due to the development of resistance by pests, the risk for non-target species is also on the rise. A case in point is the recent study in France, which has implicated the new pesticide Imidacloprid (a Neonicotinoid insecticide) as the cause for the significant loss of bee colonies. Imidacloprid is found to be a safe pesticide due to its low toxicity among mammals and hence it is used extensively for pest control in big farms. While some studies report higher levels of the pesticide in pollens and nectar of the plants, others have failed to detect any residual levels of these chemicals or their metabolites. As Kimberly stoner, a Connecticut-based entomologist says, "the pesticide is put on the seed, and the plant takes in that pesticide and moves it through the vascular system of the plant" "Bees are potentially picking them up in pollen and nectar and low levels that don't kill the bees, but that might affect their behavior and immune system" [Susan Salisbury, 2008]

A study by Laurent and Rathahao (2003) analyzed the concentrations of Imidacloprid in sunflower plants that were grown from seeds treated with the pesticide. This study was prompted by reports of unusual bee behavior by colonies that fed on these Imidacloprid treated plants. Based on radioactivity measurements, the researchers found that the plants absorbed around 10% of the pesticide treated on the seeds. Of this, 75% of the radioactivity was noticed in the cotyledons. The study also showed that the radioactivity measurements were 20 times lesser in upper leaves compared with lower leaves. This study confirmed that seed treatment affected the entire plant due to vascular translocation of the pesticide indicating the potential for bee poisoning. [Laurent, 2003]

Other studies have also reported negative effects of Imidacloprid use on the memory and brain metabolism in honeybees. Decourtye et.al (2003) showed that oral administration of Imidacloprid affected the olfactory responses of honeybees in a 'proboscis extension reflex' test. When administered 15 minutes after a PER test, it was clear that Imidacloprid compromised medium term olfactory memory. Increase in levels of cytochrome oxidase indicated pesticide-induced changes in brain metabolism and changes in neuronal transmission. [Decourtye et.al (2003)]

Gm crops and Bio pesticides

GM farming is considerably developed particularly in the United States and South American countries. GM crops that have built in pesticides are generally thought to be environmentally friendly, as they do not require the usual treatment with toxic pesticides. However, these genetically modified crops that are programmed to selectively express genes that produce peptides that have insecticidal properties could be toxic to honeybees. Since commercial production of GM crops is already a practice in many farms, studies that assess the impact of the ingestion of pollens or nectar of such genetically modified crops on bee health acquire significance. Malone et.al (2000) is one such study. This research studied the bees foraging on transgenic crops and the effects on their gut physiology, olfactory memory and longevity. In particular the effect of 'protease inhibitors', 'chitinase,' 'glucanase' and 'biotin-binding protein genes' were observed. The study concluded on a cautionary note that the biological effect of the transgenic material would depend on their type and the quantity of ingestion. Besides GM, plants are a perennial source of insecticidal proteins (expressed in their pollens and leaves) the effects of which have to be studied further. However, the results from this study showed that transgenic insecticidal proteins were much less toxic to bees and other mammals when compared to the standard industrial chemicals. [Malone A, 2001] At the moment though, there is not much research evidence to implicate GM crops induced toxicity in the chronic collapse disorder of bees.

The Changing Bee culture

The beekeeping culture has changed dramatically over the last few decades. Colonies are transported from one place to other; queen bees are artificially bred and developed. Bees are fed with huge quantities of corn syrup with little concern about their digestive metabolism. In the opinion of some researchers, commercial lease of bee colonies for pollination purposes involving frequent transporting and shifting of the bees to distant and unfamiliar locations puts considerable stress on bees. The U.S. Department of agriculture reported that, "The number of managed honey bee colonies has dropped from 5 million in the 1940s to only 2.5 million today. At the same time, the need for bee hives to supply pollination services has continued to climb. This means honey bee colonies are trucked farther and more often than ever before." Entomologists argue that many crop varieties cause nutritional stress on bees and it is indispensable that bees are fed on high quality pollens to restore their nutritional balance. So the practice of translocation bees and limiting their foraging patterns to one particular crop may create severe nutritional problems. [Benjamin P. Oldroyd, 2007]

Some researchers also opine that the lack of genetic variation among the commercially bred honeybee colonies makes them very susceptible to pathogenic infections. There are also concerns that the introduction of foreign honeybees into our country exposes them to newer environmental conditions for which they are not genetically prepared. This increases their vulnerability to local pathogens. [Benjamin P. Oldroyd, 2007]

Integrated Pest management (The Best Solution)

Pesticide usage is not a perfect and environmentally friendly solution to pest problem. Also, honeybee keepers are cautioned against the use of pesticides during the honey-producing season during which time the V Destructor population seems to rise significantly. These dangers as well as the limitations with the use of pesticides necessitate a more controlled and integrated approach to pest control. The integrated pest control approach includes a careful consideration of the life cycle of the pests along with judicious usage of pest control measures to obtain better pest control with least impact on the ecosystem. For instance, an integrated pest management approach in the honeybee colonies would be the control of the parasite V destructor.