Pollen breakdown, Chytrid fungi, Bees, Fungicides and uncomfortable truths.
In an episode of The Simpsons, which parodies the film A Few Good Men, Sideshow Bob, under interrogation from Bart and Lisa Simpson, cries out “You want the Truth. You can’t handle the truth. No truth handler you. I deride your truth handling ability!” Sideshow Bob’s philosophy on how people handle the truth is profound.
In this second and concluding part of Bee Decline and Fungicide use, I look at a group of fungi called Chytrids. This diverse group of fungi, number over 700 species and includes a number of species capable of breaking down the outer wall of pollen.
Chytrids are the oldest group of fungi known. They are aquatic and occur everywhere associated with water including damp terrestrial habitats. Very little research has been carried out on Chytrids with the exception of one species, Batrachochytrium dendrobatidis or “Bd”, which is associated with the decline and extinction of species of amphibians.
Chytrids has been found in the gut of herbivorous mammals. There may be species of Chytrids associated with the gut microbiota of bees which have a particular function of breaking down the outer wall of pollen.
Chytrids and pollen breakdown
Pollen has an outer wall composed of a chemically inert protein called sporopollenin. This has been described as the closest thing to plastic in the natural world. Chytrids are the only living organisms that can break down sporopollenin. This is highly significant as sporopollenin is made up of a compound called p-coumaric acid which is essential for the health of bees and in particular honeybees. p-coumaric acid is one of the compounds involved in switching on genes associated with the bee’s immune system and detoxification.
Figure 1 and 2 show Chytrid fungi in association with pollen from anthers. Possibly Rhizophlyctis, a chytrid ubiquitous in soil.
In Figure 3, taken from an African honey sample, the complete outer wall of pollen is missing leaving a granular mass which is pollen content. This may indicate that the enzymes secreted by Chytrids continue to function within honey and/or Chytrids are present in honey. Therefore honey is a rich source of p-coumaric acid.
Chytrids can be easily cultivated from pollen producing plants, pollen loads, pollen stores and honey.
p-coumaric acid and bee genetics
Honeybees are unusual in the insect world for having the least number of genes that are associated with detoxification and immunity. In honeybees, genes associated with detoxification and immunity are up-regulated (switched on) by p-coumaric acid derived from the breakdown of sporopollenin. A high quantity and quality of pollen is necessary to detoxify poisonous compounds and to prevent diseases from bacterial and viral pathogens.
If Chytrid species are found in the gut microbiota of bees, then they play a vital role in the health and development of bees. Removal of Chytrids from the gut microbiota environment could lead to malnutrition and shorten life expectancy of bees.
A possible truth about insecticides, fungicides and bees.
The honeybee model.
Neonicotinoids affect all bees; however, honeybees are not affected by neonicotinoids as much as bumblebees and solitary bees. The reason for this is in foraging activity. Queen bumblebees and solitary bees undertake foraging activity and are at risk of coming into direct contact with neonicotinoids. Contact made with neonicotinoids can affect the bee nervous system. In queen bees this could lead to a shortened lifespan.
In honeybees foraging activities are undertaken by foraging worker bees. Worker bees have a relatively short lifespan. In healthy honeybee colonies there are high numbers of contingency bees which always make up for any losses of foraging worker bees that fail to return. The honeybee queen is less likely to be affected by neonicotinoids and as long as she can carry on laying eggs, the colony remains healthy.
So although neonicotinoids are toxic to all bees, honeybees are less affected. It has to be taken into account that bees may be capable of detoxification of insecticidal compounds; however, fungicides which are commonly used with insecticides prevent detoxification processes.
What affects all bees are fungicides. Fungicides prevent breakdown of pollen by killing the fungi that do so. This prevents the release of p-coumaric acid from sporopollenin which therefore prevents genes associated with the bee’s immune system from being switched on.
All pesticides, including fungicides, can travel to outside the targeted areas of use. Most pesticides can persist in the environment including aquatic and soil habitats. Contact fungicides can accumulate in nectar and on pollen. Systemic fungicide bioaccumulate within pollen and biomagnify in the bee gut after large numbers of pollen are consumed.
One commonly used fungicide (pyraclostrobin), present in the environment at levels that affect all non-mammalian organisms, is often detected at high levels in foraging honeybees.
The honeybee model.
- Large amounts of pesticides are used on crops covering a large area of land.
- Contact fungicides accumulate in nectar and on pollen. Systemic fungicides bioaccumulate in pollen.
- Honeybees collect pollen and deposit pollen in pollen stores.
- Breakdown of pollen is inhibited if fungicide present.
- Young newly emerged bees consume large numbers of pollen grains.
- Pollen crushed in the proventriculus of bees releases pollen content.
- In the bee gut, pollen content masses together. Fungicides biomagnify to significant levels.
- Fungi living in the gut microbiota are killed. Nosema (depending on level of fungicide) produces spores in order to survive.
- Nutrition from pollen is greatly affected. Levels of nutrients and compounds including p-coumaric acid, from pollen are reduced.
- Bees affected by fungicides become malnourished, are vulnerable to diseases and have a shortened life expectancy.
The development of the perfect fungicide
Fungi that cause disease have always been regarded as a major threat to crop production. This has justified using enormous amounts of synthetic chemicals to reduce losses. Large amounts of research funding are used to produce more effective chemicals which can kill most groups of fungi.
Pesticides have been in use since the late nineteenth century. After the Second World War there were significant developments in the type of synthetic chemicals manufactured as pesticides, including Dichlorodiphenyltrichloroethane (DDT). The 1960s and 1970s was the period during which an explosion of chemicals were tried and tested for crop protection and food security purposes. Systemic fungicides were first used on an industrial scale during the 1970s.
In the last twenty years a new group of fungicides, strobilurin fungicides (also known as Qo fungicides), were developed. This group of fungicide was proved effective against all major groups of fungi genera. These types of fungicides are now used worldwide on almost all cereal crops. Resistant strains of fungi have developed, which has prompted more research into effective methods and more lethal formulations.
A possible truth which is hard to stomach.
The Human model
Recent research on chemicals which are associated with neurodegeneration has indicated a number of Qo fungicides produce gene expression changes similar to those in people with autism, Alzheimer’s disease and Huntington’s disease.
Pesticides including Qo fungicides are found on food that is consumed by humans of all ages.
We all have a diverse gut microbiota composed of bacteria, fungi and other microorganisms. Regular consumption of food containing small amounts of Qo fungicide may diminish the fungal composition of human gut microbiota.
Very little research has been carried out concerning the fungal component of the gut microbiota. One research paper associated with the solitary bee, Megachile rotundata, concluded that suppression of the fungal component of the gut microbiota greatly reduced the diversity of bacteria present.
The Human Model
- Qo fungicide residue on food and systemic Qo fungicides in food.
- Regular and daily consumption of foods containing Qo fungicides leads to increased concentrations of fungicide within the gut.
- In infants, 0-5 years old, Qo fungicides inhibit the establishment of fungi and diversity of bacteria in the gut microbiota.
- In adults Qo fungicide alters the gut microbiota composition by diminishing fungal and bacterial species.
- Compounds and metabolites from foods are altered.
- Gene expression, neuroinflammation and other health related conditions associated with dysbiosis of gut microbiota occurs.
A possible truth which needs urgent research.
The ecological model
There are more than 80,000 chemicals registered for use in the environment. Many pesticides are found in most fruits, vegetables and cereals consumed and are regarded as low risk, based on toxicological testing. Testing a compound for toxicity is based on the median lethal dose (LD50) which is the dose required to kill half the individuals of a tested population over a given period of time. Testing is usually carried out on mice and rats.
Toxicity limits of pesticides applied to mammals may be lethal to non-mammalian organisms including microorganisms. In the previous models, when dysbiosis of the gut microbiota occurs it may take time before effects on health are observed. In bees this may be in a shortened lifespan, in humans health conditions related to dysbiosis may occur during child development and in the elderly.
Recently published research has concluded that over the last 25 years flying insect numbers have declined by 75%. This affects food webs, biodiversity and ecosystems. All organisms with a gut have an associated gut microbiota which is unique and specialised to break down dietary intake. This includes all invertebrates, pollinators, fishes, amphibians, reptiles, birds and mammals. If the models proposed above are correct and fungicides are having an impact on the fungal composition of the gut microbiota which leads to health conditions, then we should be concerned as we are the source of all synthetic fungicides present in the environment.
Ecological systems which include microorganisms are too complex for a simple model to be proposed. All bees are keystone species, in that removal of bees from an ecosystem will lead to some plants declining, resulting in many other species, dependent on plants, to decline and eventually disappear. Honeybees, bumblebees and solitary bees, therefore, are bioindicators. Honeybees have been declining in developed countries for more than 70 years and without the intervention of beekeepers would possibly be rare or disappear from some areas altogether. A simple ecological model therefore could be based on bees. However different trophic levels have to be taken into account, in which biomagnification from one trophic level to another occurs.
Dealing with the truth and the science method
Sideshow Bob’s philosophy of how we handle the truth is profound. None of us are good handlers of the truth especially if it involves ourselves, a relationship, or as a beekeeper, honeybees. We may exhibit emotions from total denial to hysteria; an entire spectrum of handling the truth exists.
Science is a method which excludes emotions. It is based on four simple precepts, making an observation, producing a hypothesis, testing the hypothesis and predicting the future. An observation has been made that over the last twenty years there has been a 75% decline in the number of flying insects and over the last 70 years honeybees have been declining. Also there is evidence that more children are diagnosed within the Autism Spectrum Disorder (ASD) and Alzheimer’s disease is becoming more prevalent.
Two null hypotheses based on these observations are proposed for honeybees and humans.
1. Null hypothesis relating to honeybees
Systemic fungicides are not bioaccumulated in pollen and biomagnified in the bee gut leading to dysbiosis. Fungicides are not related to the appearance of Nosema spores. Fungicides do not remove Chytrids and therefore prevent sporopollenin breakdown to produce of p-coumaric acid. Fungicides do not lead to malnutrition in honeybees and adversely affect the health of bee colonies.
2. Null hypothesis relating to humans
Harmful fungicides used in food production are not on or in food which are consumed. Fungicides do not concentrate within the gut leading to dysbiosis and health related conditions. Fungicides do not alter the development of gut microbiota in young children and elderly people leading to long-term health conditions.
These hypotheses are for the manufacturers, distributers and marketers of fungicides to test, based on the assumption that they have the resources and finances to do so.
Moving on from a Walt Disney model of Natural Science.
The authorities that govern everything bee-related have been highly successful in raising funding for projects involving pollination, which is a process carried out by many organisms including fruit bats and humming birds. This will never lead to any real understanding of issues concerning the decline of honeybees and other pollinators. Funding and focus is required for bee nutrition and pollen research. How pollen is broken down, what plants are essential for honeybees, are there medicinal values to the pollen collected and many other projects involving fungi and gut microbiota. This would lead to a better understanding of bees and associated organisms. Only from this research will we ever find a basis for examining other associations in a fragile ecosystem which includes humans.
Some of us know, having watched the X-Files, the truth is out there. Let’s hope we can handle it.